exam Flashcards
What is a ruler used to measure
A rule (ruler) is used to measure length for distances between 1mm and 1meter
SI unit for length
SI unit for length is the meter (m)
How to find out volume of regular object
To find out volume of regular object, use mathematical formula
how to find out volume of irregular object
To find out volume of irregular object, put object into measuring
cylinder with water. When object added, it displaces water,
making water level rise. Measure this rise. This is the volume.
what is a MICROMETER SCREW GAUGE used for
Used to measure very small distances
Determination of the diameter ‘d’ of a wire
How to use a micrometer screw gauge
Place the wire between the anvil and spindle end as indicated in
the diagram.
Rotate the thimble until the wire is firmly held between the anvil
and the spindle.
The ratchet is provided to avoid excessive pressure on the wire. It
prevents the spindle from further movement - squashing the wire
How to take a reading on a micrometer screw gauge
First look at the main scale. This has a linear scale reading on it. The long lines are every millimetre the shorter ones
denote half a millimetre in between.
what do clocks measure
Interval of time is measured using clocks
SI unit for time
SI unit for time is the second(s)
How to find the amount of time it takes a pendulum to make a spin
To find the amount of time it takes a pendulum to make a spin,
time ~25 circles and then divide by the same number as the
number of circles.
Principle of conservation of linear momentum: when bodies in a
system interact, total momentum remains constant provided no
external force acts on the system. What is speed
Speed is the distance an object moves in a time frame. It is
measured in meters/second (m/s) or kilometers/hour (km/h).
Speed equation
𝑺𝒑𝒆𝒆𝒅 = 𝑻𝒐𝒕𝒂𝒍 𝑫𝒊𝒔𝒕𝒂𝒏𝒄𝒆/𝑻𝒐𝒕𝒂𝒍 𝑻𝒊𝒎e
Is speed a vector or scalar quantity
Speed is a scalar quantity
how to calculate distance travelled on SPEED/TIME GRAPHS
Area under the line equals to the distance travelled
Gradient of speed/time graph
𝐺𝑟𝑎𝑑𝑖𝑒𝑛𝑡 = 𝑦2−𝑦1/𝑥2−𝑥1
how to calculate distance travelled with constant speed
With constant speed: 𝑆𝑝𝑒𝑒𝑑 × 𝑇𝑖𝑚e
how to calculate distance travelled with constant acceleration
With constant acceleration:
𝐹𝑖𝑛𝑎𝑙 𝑆𝑝𝑒𝑒𝑑+𝐼𝑛𝑖𝑡𝑖𝑎𝑙 𝑆𝑝𝑒𝑒𝑑 / 2 × 𝑇𝑖𝑚e
Acceleration equation
𝑨𝒄𝒄𝒆𝒍𝒆𝒓𝒂𝒕𝒊𝒐𝒏 =
𝑭𝒊𝒏𝒂𝒍 𝑺𝒑𝒆𝒆𝒅 − 𝑰𝒏𝒊𝒕𝒊𝒂𝒍 𝑺𝒑𝒆𝒆𝒅 / 𝑻𝒊𝒎𝒆 𝑻𝒂𝒌𝒆n
What is acceleration
Acceleration is the rate of change in velocity per unit of time,
measured in meters per second, or m/s2
Is acceleration a vector or scalar quantity
Acceleration is a vector quantity
what does positive acceleration mean
Positive acceleration means the velocity of a body is increasing
What does negative acceleration mean
Deceleration or negative acceleration means the velocity of a
body is decreasing
what happens if the acceleration is not constant
If acceleration is not constant, the speed/time graph will be
curved.
What is the downwards acceleration of an object caused by
The downwards acceleration of an object is caused by gravity.
This happens most when an object is in free. Objects are slowed
down by air resistance. Once air resistance is equal to the force
of gravity, the object has reached terminal velocity. This means
that it will stay at a constant velocity. acceleration of free fall for
a body near to the Earth is constant (G=10m/s)
What is mass
Mass: amount of matter an object contains, and is a property
that ‘resists’ change in motion
what is weight
Weight is the force of gravity acting on an object, measured in
Newtons, and given by the formula:
Weight formula
𝑾𝒆𝒊𝒈𝒉𝒕 = 𝑴𝒂𝒔𝒔 × 𝑮𝒓𝒂𝒗𝒊𝒕y
what can weights and masses be compared by
Weights (and hence masses) may be compared using a balance
Density equation
𝑫𝒆𝒏𝒔𝒊𝒕𝒚 = 𝑴𝒂𝒔𝒔/𝑽𝒐𝒍𝒖𝒎e
how to work out density of a liquid
Density of a liquid: place measuring cylinder on a balance, fill
measuring cylinder with the liquid. The change in mass is mass of
liquid and volume is shown on the scale, then use formula.
How to find out density of a solid
Finding the volume: To find out volume of a regular object,
use mathematical formula. To find out volume of an irregular
object, put object into a measuring cylinder with water and
the rise of water is the volume of the object
Finding the mass: weigh object on a scale and use formula
how to work out wether something will float or sink in the water
The density of water is 1g/cm3
if an object has a greater density
than that, then it will sink in water, and if the object’s density is
less than that, then it will float in water
What will a force produce
A force may produce a change in size and shape of a body, give an
acceleration or deceleration or a change in direction depending on
the direction of the force.
What happens when there is no resultant force acting on a body
If there is no resultant force acting on a body, it either remains at
rest or continues at constant speed in a straight line
what is friction
Friction: the force between two surfaces which impedes motion
and results in heating
What is a form of friction
Air resistance is a form of friction
what do springs extend in proportion to
Springs extend in proportion to load, as long as they are under their proportional limit.
What is limit of proportionality
Limit of proportionality: point at which load and extension are no longer proportional
what is elastic limit
Elastic limit: point at which the spring will not return to
its original shape after being stretched
Load equation
𝐿𝑜𝑎𝑑(𝑁) = 𝑆𝑝𝑟𝑖𝑛𝑔 𝐶𝑜𝑛𝑠𝑡𝑎𝑛𝑡 × 𝑒𝑥𝑡𝑒𝑛𝑠𝑖𝑜𝑛 𝑭 = 𝒌𝒆
force equation
F=MA
𝑭𝒐𝒓𝒄𝒆 = 𝑴𝒂𝒔𝒔 × 𝑨𝒄𝒄𝒆𝒍𝒆𝒓𝒂𝒕𝒊𝒐𝒏
What is force measured in
Force is measured in Newtons
what is the amount of force needed to give 1kg an acceleration of 1m/s2
1 Newton is the amount of force needed to give 1kg an
acceleration of 1m/s2
What does an object at steady speed in circular orbit do
An object at steady speed in circular orbit is always accelerating as
its direction is changing, but it gets no closer to the center
what is centripetal force
Centripetal force is the force acting towards the center of a circle.
It is a force that is needed, not caused, by circular motion
What is centrifugal force
Centrifugal force is the force acting away from the center of a
circle. This is what makes a slingshot go outwards as you spin it.
The centrifugal force is the reaction to the centripetal force. It has
the same magnitude but opposite direction to centripetal force.
newtons first law
First law of motion: If no external for is acting on it, an object will,
if stationary, remain stationary, and if moving, keep moving at a
steady speed in the same straight line
Newtons second law
Second law of motion: 𝑭 = 𝒎𝒂
newtons third law
Third law of motion: if object A exerts a force on object B, then
object B will exert an equal but opposite force on object A
Moment equation
𝑴𝒐𝒎𝒆𝒏𝒕(𝑵𝒎) = 𝑭𝒐𝒓𝒄𝒆(𝑵) × 𝑫𝒊𝒔𝒕𝒂𝒏𝒄𝒆 𝒇𝒓𝒐𝒎 𝑷𝒊𝒗𝒐𝒕(𝒎)
what is the clockwise and anticlockwise moment in equilibrium
In equilibrium, clockwise moment = anticlockwise moment
What does increasing force or distance from the pivot do to the moment of a force
Increasing force or distance from the pivot increases the moment
of a force
what is a lever
Levers are force magnifiers
Why is turning a bolt easier with a wrench
Turning a bolt is far easier with a wrench because distance
from pivot is massively increased, and so is the turning effect.
what is the centre of mass
Centre of mass: imaginary point in a body
where total mass of body seems to be acting
how to work out the centre of mass
Working out the center of mass:
Mark three points on the edge of the card
Make a hole using a pin on each point
Hang it on a cork board and make a line when it is stable
Do this for all three points Where all three lines intersect, this is the center of mass
when will an object be in stable equilibrium
An object will be in stable equilibrium when it returns to its
original position given a small displacement
What does an object need to start rotating
For an object to start rotating it needs to have an unbalanced
moment acting on it
what is a scalar quantity
A scalar is a quantity that only has a magnitude (so it can only be
positive) for example speed.
What is a vector quantity
A vector quantity has a direction as well as a magnitude, for
example velocity, which can be negative
linear momentum equation
Linear momentum: product of mass and velocity
𝑝 = 𝑚𝑣
Principle of conservation of linear momentum:
when bodies in a system interact, total momentum remains constant provided no
external force acts on the system.
𝑚𝐴𝑢𝐴 + 𝑚𝐵𝑢𝐵 = 𝑚𝐴𝑣𝐴 + 𝑚𝐵𝑣B
Impulse equation
product of force and time for which it acts
𝐹𝑡 = 𝑚𝑣 – 𝑚u
What is energy
amount of work and its measured in Joules (J)
Why may an object have energy
An object may have energy due to its motion or its position
conservation of energy
Conservation of energy: energy cannot be created or destroyed,
when work is done, energy is changed from one form to another
Energy can be stored
Kinetic energy
Due to motion
gravitational energy
From potential to fall
Chemical energy
In chemical bonds
strain energy
Compress/stretch
Nuclear energy
Atoms rearranged/split
internal energy
Motion of molecules
Electrical energy
Carried by electrons
light energy
Carried in light waves
Sound energy
Carried in sound waves
Kinetic energy equation
𝐾𝑖𝑛𝑒𝑡𝑖𝑐 𝑒𝑛𝑒𝑟𝑔𝑦 = 1/2 × 𝑀𝑎𝑠𝑠 × 𝑉𝑒𝑙𝑜𝑐𝑖𝑡y²
𝑲. 𝑬. = 𝟏/𝟐 𝒎v²
Gravitational potential energy equation
𝐺𝑟𝑎𝑣𝑖𝑎𝑡𝑖𝑜𝑛𝑎𝑙 𝑃𝑜𝑡𝑒𝑛𝑡𝑖𝑎𝑙 𝐸𝑛𝑒𝑟𝑔𝑦 = 𝑀𝑎𝑠𝑠 × 𝐺𝑟𝑎𝑣𝑖𝑡𝑦 × 𝐻𝑒𝑖𝑔ℎ𝑡
𝑮.𝑷. 𝑬. = 𝒎𝒈h
Example of conversion of energy
A book on a shelf has gravitational potential energy, if it falls of the shelf it will have kinetic energy
describe renewable and non renewable energy
Renewable sources are not exhaustible
Non-renewable sources of energy are exhaustible
What is the source of most of our energy
The sun is the source of energy for all our energy resources except
geothermal, nuclear and tidal
how is energy made in the sun
In the sun, energy is created through a process called nuclear
fusion: hydrogen nuclei are pushed together to form helium.
What is efficiency
Efficiency: how much useful work is done with energy supplied
efficiency equation
𝑬𝒇𝒇𝒊𝒄𝒊𝒆𝒏𝒄𝒚 =𝑼𝒔𝒆𝒇𝒖𝒍 𝒆𝒏𝒆𝒓𝒈𝒚 𝒐𝒖𝒕𝒑𝒖𝒕 / 𝑬𝒏𝒆𝒓𝒈𝒚 𝒊𝒏𝒑𝒖𝒕 × 𝟏𝟎𝟎%
𝑬𝒇𝒇𝒊𝒄𝒊𝒆𝒏𝒄𝒚 = 𝑼𝒔𝒆𝒇𝒖𝒍 𝒑𝒐𝒘𝒆𝒓 𝒐𝒖𝒕𝒑𝒖𝒕 /𝑷𝒐𝒘𝒆𝒓 𝒊𝒏𝒑𝒖𝒕 × 𝟏𝟎𝟎%
What is work
Work is done whenever a force makes something move.
The unit for work is the Joule (J).
1 joule of work = force of 1 Newton moves an object by 1 meter
Work equation
𝑾𝒐𝒓𝒌 𝒅𝒐𝒏𝒆 (𝑱) = 𝑭𝒐𝒓𝒄𝒆 (𝑵) × 𝑫𝒊𝒔𝒕𝒂𝒏𝒄𝒆 (𝒎)
𝑾 = 𝑭𝑫
What is power
Power is the rate of work
The unit for power is Watts (W)
Power equation
𝑷𝒐𝒘𝒆𝒓 (𝑾) = 𝑾𝒐𝒓𝒌 𝑫𝒐𝒏𝒆 (𝑱) / T𝒊𝒎𝒆 𝑻𝒂𝒌𝒆𝒏 (𝒔)
pressure equation (solid)
𝑷𝒓𝒆𝒔𝒔𝒖𝒓𝒆 (𝑷𝒂) = F𝒐𝒓𝒄𝒆 (𝑵) / 𝑨𝒓𝒆𝒂 (𝒎𝟐)
𝑷 = 𝑭 / 𝑨
Unit: Pascals (Pa) = N/m2
pressure equation (liquid)
𝑷𝒓𝒆𝒔𝒔𝒖𝒓𝒆(𝑷𝒂) = 𝑫𝒆𝒏𝒔𝒊𝒕𝒚(𝒌𝒈/𝒎𝟑) × 𝑮𝒓𝒂𝒗𝒊𝒕𝒚(𝒎/𝒔𝟐) × 𝑯𝒆𝒊𝒈𝒉𝒕(𝒎) 𝑷 = 𝒉𝝆𝒈
What is the pressure in 10m water
At a depth of 10m in water, the pressure is always 100,000 Pa
(1bar) and is constant for each further 10m.
atmospheric pressure equation
1 atm = 101.325 X 103 Pa = 101 KPa
What is a manometer
A manometer measures the
pressure difference.
The height difference shows
the excess pressure in addition
to the atmospheric pressure.
What is a barometer
Tube with vacuum at the topand mercury filling the rest.
Pressure of the air pushesdown on reservoir, forcingmercury up the tube.
Measure height of mercury
~760 mm of mercury is 1 atm
what is a solid
Fixed shape and volume Strong forces of attraction between particles Fixed pattern (lattice) Atoms vibrate but can’t change position: fixed volume and shape
What is a liquid
Fixed volume but changes shape depending on its container
Weaker attractive forces than solids
No fixed pattern, liquids take shape of their container
Particles slide past each other
what is a gas
No fixed shape or volume, gases fill up their containers
Almost no intermolecular forces
Particles far apart, and move quickly
Collide with each other and bounce in all directions
Pressure in gasses
The pressure gases exert on a container is due to the particles
colliding on the container walls.
If the volume is constant, then increasing the temperature will
increase the pressure.
brownian motion
Gas molecules move at a random motion
This is because of repeated collisions with other gas molecules
Small molecules move much faster and have higher energy than larger molecules
The small particles can help move the larger particles
Brownian motion can be seen visually in smoke
What is evaporation
It is the escape of the more energetic particles and occurs
constantly on the surface of liquids
what happens if more energetic particles escape liquid
If more energetic particles escape, liquid contains few high energy
particles and more low energy particles so average temperature
decreases.
How can evaporation be accelerated by
Evaporation can be accelerated by:
o Increasing temperature: more particles have energy to escape
o Increasing surface area: more molecules are close to the
surface
o Reduce humidity level in air: if the air is less humid, fewer
particles are condensing.
o Blow air across the surface: removes molecules before they can
return to the liquid
explain thermal expansion
Solids, liquids and gasses expand when they are heated as atoms
vibrate more and this causes them to become further apart, taking
up a greater volume.
Due to differences in molecular structure of the different states of
matter, expansion is greatest in gases, less so in liquids and lowest
in solids
Applications and consequences of thermal expansion:
Overhead cables have to be slack so that on cold days, when
they contract, they don’t snap or detach.
Gaps have to be left in bridge to allow for expansion
Bimetal thermostat: when temperature gets too high, bimetal
strip bends, to make contacts separate until temperature falls
enough, then metal strip will become straight again and
contacts touch, to maintain a steady temperature
For a fixed mass of gas at constant pressure, the volume is directly
proportional to the Kelvin temperature
How to find the fixed mass of gas at constant pressure
For a fixed mass of gas at constant pressure, the volume is directly
proportional to the Kelvin temperature
What can a physical property that varies with temperature be used for
A physical property that varies with temperature may be used for
measurement of temperature
how does a liquid-in-glass thermometer work
As temperature rises or falls, the liquid (mercury or alcohol)
expands or contracts.
Amount of expansion can be matched to temperature on a
scale.
How does a thermistor thermometer work
The probe contains a thermistor
The thermistor is a material that becomes a better electrical
conductor when the temperature rises (semi-conductor)
So when temperature increases, a higher current flows from a
battery, causing a higher reading on the meter
how does a thermocouple thermometer work
The probe contains 2 different metals joined metals to form 2
junctions.
The temperature difference causes a tiny voltage which makes a
current flow.
A greater temperature difference gives a greater current.
Thermocouple thermometers are used for high temperatures
which change rapidly and have a large range (-200C° to 1100°C)
What are fixed points
Fixed points are definite temperatures at which something
happens and are used to calibrate a thermometer. For example,
melting and boiling point of water
how to calibrate a thermometer
Place thermometer in melting ice, this is 0 °C.
Place thermometer in boiling water, this is 100 °C
What is thermometer sensitivity
Sensitivity: change in length or volume per degree
How to increase thermometer sensitivity
To increase sensitivity:
Thinner capillary
Less dense liquid
Bigger bulb
how to increase thermometer range
Range: change the upper and lower fixed points
what is thermometer linearity and responsiveness
Linearity: change the distance between intervals
Responsiveness: how long it takes for the thermometer to react
to a change in temperature
What is melting
This is when a solid turns into a liquid.
Temperature increases thus kinetic energy in solid increases and
particles vibrate more rapidly but there is no increase in
temperature of the substance when melting because thermal
energy supplied is instead being used to break bonds between
particles of the solid thus making it into a liquid.
what is boiling point
Boiling point is the temperature at which a substance boils
What is boiling
This is when a liquid turns into a gas
Temperature increases thus kinetic energy in liquid increases and
particles vibrate more rapidly but there is no increase in
temperature of the substance when boiling because thermal
energy supplied is instead being used to break bonds between
particles of the liquid thus making it into a gas.
What is melting point
Melting point is the temperature at which a substance melts
What is the difference between boiling and evaporation
Boiling occurs at a fixed temperature and throughout the liquid
Evaporation occurs at any temperature and only on the surface
What is the latent heat of fusion
The latent heat of fusion is the amount of energy needed to melt
1Kg of a substance.
What is the latent heart of vaporisation
The latent heat of vaporization is the amount of energy needed to
boil 1Kg of a substance
Latent heat equation
𝑆𝑝𝑒𝑐𝑖𝑓𝑖𝑐 𝐿𝑎𝑡𝑒𝑛𝑡 𝐻𝑒𝑎𝑡 𝑜𝑓 𝐹𝑢𝑠𝑖𝑜𝑛 = 𝐸𝑛𝑒𝑟𝑔𝑦 𝑇𝑟𝑎𝑛𝑠𝑓𝑒𝑟𝑟𝑒𝑑 / 𝑀𝑎𝑠𝑠
𝑆𝑝𝑒𝑐𝑖𝑓𝑖𝑐 𝐿𝑎𝑡𝑒𝑛𝑡 𝐻𝑒𝑎𝑡 𝑜𝑓 𝑉𝑎𝑝𝑜𝑟𝑖𝑧𝑎𝑡𝑖𝑜𝑛 = 𝐸𝑛𝑒𝑟𝑔𝑦 𝑇𝑟𝑎𝑛𝑠𝑓𝑒𝑟𝑟𝑒𝑑 / 𝑀𝑎𝑠𝑠
What is condensation
Condensation is when a gas turns back into a liquid.
what happens when a gas is cooled
When a gas is cooled, the particles lose energy. They move more
and more slowly. When they bump into each other, they do not
have enough energy to bounce away again so they stay close
together, and a liquid forms
What happens when a liquid cools
When a liquid cools, the particles slow down even more.
Eventually they stop moving except for vibrations and a solid
forms.
good vs bad conductors
Good conductors are used whenever heat is required to travel
quickly through something
Bad conductors (insulators) are used to reduce the amount of heat
lost to the surroundings
What is conduction
Conduction is the flow of heat through
matter from places of higher temperature to
places of lower temperature without
movement of the matter as a whole
what happens in non metals when heat is supplied to something
In non-metals - when heat is supplied to
something, its atoms vibrate faster and pass
on their vibrations to the adjacent atoms.
How does conduction happen in metals
In metals – conduction happens in the previous way and in a
quicker way –electrons are free to move, they travel randomly in
the metal and collide with atoms and pass on the vibrations.
What is convection
Convection is the flow of heat through a
fluid from places of higher temperature in
places of lower temperature by movement
of the fluid itself.
how does the convection cycle work
As a fluid (liquid or gas) warms up, the
particles which are warmer become less
dense and rise.
They then cool and fall back to the heat
source, creating a cycle called convection current.
As particles circulate they transfer energy to other particles. If a
cooling object is above a fluid it will create a convection current
What is radiation
Radiation is the flow of heat from one place to another by means
of electromagnetic waves
what is thermal radiation
Thermal radiation is mainly infra-red waves, but very hot objects
also give out light waves. Infra-red radiation is part of the
electromagnetic spectrum.
What does a reflector do
A reflector reflects thermal radiation,
therefore is a bad absorber.
what does an emitter do
An emitter will cool down quickly, an
absorber will heat up more quickly and a
reflector will not heat up quickly
How does a solar panel work
Solar panel: the sun’s thermal radiation is absorbed by a matt
black surface and warms up the pipes containing water
how does a refrigerator work
Refrigerator: the freezer compartment is located at the top of the
refrigerator. It cools down the air which then sinks. Any warm air
rises to the top and then is cooled. This creates a convection
current which maintains a cold temperature
why are metals used in cooking pans
Metals used in cooking pans because they conduct heat well
Consequences of energy transfer:
Metal spoon
convection current
Black sauce pan
Metal spoon in a hot drink will warm up because it conducts heat
Convection currents create sea breezes. During the day the land is
warmer and acts as heat source. During the night the sea acts as
the heat source.
A black saucepan cools better than a white one, white houses
stay cooler than dark ones
How do waves transfer energy
Waves transfer energy without transferring matter
what is frequency
Frequency: the number of waves passing any point per second
measured in hertz (Hz)
What is a period (waves)
Period: time taken for one oscillation in seconds
what is a wavefront
Wavefront: the peak of a transverse wave or the compression of
a longitudinal wave
What is wave speed
Speed: how fast the wave travels measured in m/s
what is wave length
Wavelength: distance between a point on one wave to the
equivalent point on the next wave in meters
What is amplitude
Amplitude: maximum distance a wave moves from its rest
position when a wave passes
describe transverse waves
Travelling waves in which oscillation is perpendicular to direction of travel
Has crests and troughs
For example, light, water waves and vibrating string
Describe Longitudinal Waves
Travelling waves in which oscillation is parallel to direction of travel.
Has compressions and rarefactions
For example, sound waves
what happens in refraction
Speed and wave length is reduced but frequency stays the same
and the wave changes direction
Waves slow down when they pass from a less to a more dense
material and vice versa
What happens when waves are slowed down of sped up
When wave is slowed down, it is refracted towards normal (i > r)
When wave is sped up, it is refracted away from normal (i < r)
is deep water denser or less dense than shallow water
Deep water is denser than shallow water
What happens when water wave travels from deep to shallow
When water wave travels from deep to shallow; speed decreases, wavelength decreases and frequency remains constant
What happens when water wave travels from shallow to deep
When water waves travel from shallow to deep; speed increases wavelength increases and frequency remains constant
Describe reflection
Waves bounce away from surface at same angle they strike it
Angle of incidence = angle of reflection
Speed, wavelength and frequency are unchanged by reflection
Describe diffraction
Waves bend round the sides of an obstacle, or spread out as they pass through a gap. Wider gaps produce less diffraction. When the gap size is equal to the wavelength, maximum diffraction occurs
what produce reflections
Plane (flat) mirrors produce a reflection
What do rays from an object reflect off the mirror into
Rays from an object reflect off the mirror into our eyes,
but we see them behind the mirror
what properties do reflected images have
Image is the same size as the object
Image is the same distance from the mirror as the object
A line joining equivalent points of the image and object meet
the mirror at a right angle
Image is virtual: no rays actually pass through the image and
the image cannot be formed on a screen
Laws of reflection
Angle of incidence = angle of reflection
The incident ray, reflected ray and normal are always on the same
plane (side of mirror)
what is refraction
Refraction is the bending when light travels from one medium to
another
What is the critical angle
Angle at which refracted ray is parallel to the surface of material.
If angle of incidence is greater than the critical angle there is no
refracted ray, there is total internal reflection.
If angle of incidence is less than the critical angle the incidence
ray will split into a refracted ray and a weaker reflected ray
How do optical fibres work in communications and medicine
Light put in at one end is totally internally reflected until it comes
out the other end.
Used in communications: signals are coded and sent along the
fiber as pulses of laser light
Used in medicine: an endoscope, an instrument used by surgeons
to look inside the body; contains a long bundle of optic fibers.
Principal focus
Principal focus: the point where rays parallel to the principal axis
converge with a converging lens.
Focal length
Focal length: distance from principle focus and the optical center
Principal axis
Principal axis: line that goes through optical center, and the 2 foci
Optical center
Optical center: the center of the lens
Real image
Real: image can be caught on a screen
Virtual image
Virtual: image cannot be caught on a screen
Why is something a real or virtual image
Real: when object is further away from the optical centre than F’ is
Virtual: When the object is closer to the optical centre than F’ is
what happens when light is refracted by a prism
When light is refracted by a prism, the incidence ray is not parallel to the emergent ray, since the prism’s sides are not parallel.
How is white light dispersed through a prism
If a beam of white light is
passed through a prism it is dispersed into a spectrum.
White light is a mixture of colors, and the prism refracts each
color by a different amount – red is deviated least & violet most
properties of all electromagnetic waves
Travel at the speed of light: 3 × (10 to the power of 8) m/s
Don’t need a medium to travel through (travel through a vacuum)
Can transfer energy
Are produced by particles oscillating or losing energy in some way
Are transverse waves
Uses of Radio waves
Radio waves: radio and television communications
uses of microwaves
Microwaves: satellite television and telephones
Safety issue: cause internal heating of body tissues
Uses of infrared
Infrared: electrical appliances (radiant heaters and grills), remote
controllers for televisions and intruder alarms
uses of x rays
X-rays: medicine (x-ray photography and killing cancer cells) and
security
o Safety issue: is a mutagen, it cause cancer (mutations)
Uses of monochromatic
Monochromatic: light of a single wavelength and color (used in
lasers)
how does a loudspeaker work (sound waves)
Sound waves come from a vibrating source e.g. loudspeaker
As the loudspeaker cone vibrates, it moves forwards and
backwards, which squashes and stretches the air in front
As a result, a series of compressions (squashes) and rarefactions
(stretches) travel out through the air, these are sound waves.
Properties of sound waves
Sound waves are longitudinal: they have compressions and
rarefactions and oscillate backwards and forwards.
Humans can hear frequencies between 20 and 20 000Hz.
Sound waves need a medium to travel through.
ultrasound waves
Ultrasound Waves: high frequency sound waves, medically used
to look at structures and organs inside the human body, i.e. to
form an image of a fetus in a pregnancy
What is compression and rarefaction
Compression: high pressure section of the wave
Rarefaction: low pressure section of the wave
what does high frequency and amplitude do
The higher the frequency, the higher the pitch.
The higher the amplitude, the louder the sound.
Speed of sound in concrete, water and air
Medium State speed
Concrete Solid 5000 m/s
Pure Water Liquid 1400 m/s
Air Gas 330 m/s
PROPERTIES OF MAGNETS
Has a magnetic field around it
Has 2 opposite poles (North and South) which exert forces on
other magnets. Like poles repel and unlike poles attract.
Will attract magnetic materials by inducing (permanent or
temporary) magnetism in them.
Will exert little or no force on a non-magnetic material
The direction of an electric field at a point is the direction of the
force on a positive charge at that point
what is induced magnetism
Magnets attract materials by inducing magnetism in them; the
material becomes a magnet as well.
The side of the material facing the magnet will become the
opposite pole as the magnet.
MAGNETISATION METHODS
A piece of steel becomes permanently magnetized when placed
near a magnet, but its magnetism is usually weak.
It can be magnetized more strongly by stroking it with one end of
a magnet
Most effective method: place it in a solenoid and pass a large,
direct current (d.c.) through the coil.
DEMAGNETISATION METHODS
If a magnet is hammered, its atomic magnets are thrown out of
line and it becomes demagnetized.
Heating a magnet to a high temperature also demagnetize it.
Most efficient method: place magnet inside a solenoid connected
to an alternating current (a.c.) supply
Use of permanent magnet
Design: Hard magnetic material Use: For applications where magnetism is needed over long periods – fridge doors
use of electromagnet
Design: Uses a solenoid to create magnetic field Use: For applications where magnetic field needs to be turned on & off - scrap metal moving
how to detect an electrostatic charge using a leaf electroscope.
You can detect an electrostatic charge using a leaf electroscope.
If a charged object is placed near the cap, charges are induced.
The metal cap gets one type of charge (positive or negative)
and the metal stem and gold leaf get the other type of charge
so they repel each other
What are the 2 types of charges
There are 2 types of charges: positive and negative.
Unlike charges attract and like charges repel.
what is the electric field
Electric field: region in which electric charge experiences a force
What is a conductor
Conductors: materials that let electrons pass through them
Metals are the best electrical conductors as they have free
electrons.
what are insulators
Insulators: materials that hardly conduct at all.
o Their electrons are tightly held to atoms and hardly move, but
they can be transferred by rubbing
What is the SI unit of charge
The SI unit of charge is the Coulomb (C).
what are the different types of electric field lines
Parallel plates
Point charge
+ve and -ve
+ve and +ve
What is an induced charge
A charge that “appears” on an uncharged object because of a
charged object nearby
For example if a positively charged rod is brought near a small
piece of aluminum foil, electrons in foil are pulled towards rod,
which leaves the bottom of the foil with a net positive charge.
The attraction is stronger than repulsion because the attracting
charges are closer than the repelling ones
What is current
Current: a flow of charge, the SI unit is the Ampere (A).
An ammeter measures the current in a circuit and is connected in
series
Current is a rate of flow of charge.
𝐶ℎ𝑎𝑟𝑔𝑒 (𝐶) = 𝐶𝑢𝑟𝑟𝑒𝑛𝑡 (𝐴) × 𝑇𝑖𝑚𝑒 (𝑠)
𝑄 = 𝐼𝑡
Current follows path of least resistance
what is conventional current
The conventional current is the opposite of what actually
happens.
What is Electromotive force (EMF)
The maximum voltage a cell can produce is called the electromotive force (EMF), measured in volts.
When a current is being supplied, the voltage is lower because of
the energy wastage inside the cell.
A cell produces its maximum PD when not in a circuit and not supplying current.
what is potential difference
Potential difference, or PD for short, is also known as voltage.
What is voltage
Voltage is the amount of energy the cell gives the electrons it
pushes out. Voltage is measured in volts (V) and is measured by a
voltmeter (connected in parallel). If a cell has 1 Volt, it delivers 1
Joule of energy to each coulomb of charge (J/C).
voltage equation
𝑉𝑜𝑙𝑡𝑎𝑔𝑒 = 𝐸𝑛𝑒𝑟𝑔𝑦 / 𝐶ℎ𝑎𝑟𝑔𝑒
𝑉 =𝐸 / C
Resistance equation
𝑅𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒 = 𝑉𝑜𝑙𝑡𝑎𝑔𝑒 / 𝐶𝑢𝑟𝑟𝑒𝑛𝑡 = (Ω) = 𝑉 / 𝐼
factors affecting resistance
Factors affecting resistance:
Length
Cross-sectional area
Material
Better conductor = less resistance
Temperature
For metal conductors higher temperature = more resistance
For semi-metal conductors higher temperature = less
resistance
CHARACTERISTICS OF A RESISTOR
Ohm’s law states that voltage across a resistor is directly
proportional to the current through it. This is only true if the
temperature of the resistor remains constant.
What does 1 Watt equal to
1 Watt is 1J/s
electrical power equation
𝐸𝑙𝑒𝑐𝑡𝑟𝑖𝑐𝑎𝑙 𝑝𝑜𝑤𝑒𝑟 = 𝑉𝑜𝑙𝑡𝑎𝑔𝑒 (𝑉) × 𝐶𝑢𝑟𝑟𝑒𝑛𝑡 (𝐴)
Electrical energy equation
𝐸𝑙𝑒𝑐𝑡𝑟𝑖𝑐𝑎𝑙 𝑒𝑛𝑒𝑟𝑔𝑦 = 𝑉𝑜𝑙𝑡𝑎𝑔𝑒 (𝑉) × 𝐶𝑢𝑟𝑟𝑒𝑛𝑡 (𝐴) × 𝑡𝑖𝑚𝑒 (𝑠)
cell function
Supplies electrical
energy. Larger terminal
(left) is positive (+).
Battery function
Supplies electrical energy. A battery is more than one cell. Larger terminal (left) is positive (+)
DC supply function
Flows in one direction
AC Supply function
Flows in both direction
Switch function
Allows current only to
flow when the switch is
closed
fixed resistor function
Restrict the flow of
current.
Variable resistor function
Used to control current
(by varying the
resistance)
thermistors function
Resistor whose
resistance varies with
temperature
Light dependent resistors function
Resistor whose
resistance varies with
light intensity
Lamp function
Transducer which
converts electrical
energy to light
Ammeter function
Measure current
voltmeter function
Measure voltage
Galvanometers function
Type of sensitive ammeter; instrument for detecting electric current.
Transformer function
Two coils of wire linked by an iron core. Transformers are used to increase and decrease AC voltages.
Bell functinon
Transducer which
converts electrical
energy to sound
fuse function
A safety device which will 'blow' (melt) if current flowing through it exceeds specified value, breaking circuit
Relay function
An electrically operated switch, e.g. a 9V battery circuit connected to the coil can switch a 230V AC mains circuit (the electromagnet is used to pull away the contacts and vice versa)
factors of series circuit and parallel circuit
The current at any point in a series circuit is the same
The current splits at each branch in a parallel circuit so the total
current is always greater than the current in one branch
What is the combined resistance of 2 resistors in parallel
The combined resistance of 2 resistors in parallel is less than
that of either resistor by itself
Advantages of putting lamps in parallel
Advantages of putting lamps in parallel are:
o If one lamp breaks, the other still works
o Each lamp gets maximum PD
Current in series and parallel
In series: PD across the supply = PD across all the components
combined
In parallel: Current across the source = sum of currents in the
separate branches
what does a potential divider do
A potential divider divides the voltage into smaller parts.
What is a thermistor
Thermistor: input sensor and a transducer. It is a
temperature-dependent resistor. At higher
temperature there is less resistance.
What is a light dependent resistor
Light dependent resistor (LDR): input sensor and a
transducer. When light intensity increases,
resistance decreases.
what is a relay
A switch operated by an electromagnet
How do Normal Closed Relay and Normally Open Relays work
Normal Closed Relay: When coil not energised, switch is closed, completing circuit
Normally Open Relay: When coil is energised, switch is closed, completing circuit
what is a diode
A device that has an extremely high resistance in one direction
and a low resistance in the other, therefore it effectively only
allows current to flow in one direction
Forward bias is when the diode is pointing in the direction of the
conventional current and reverse bias is the opposite
It can be used in a rectifier; turns AC current into DC current.
What is an analogue signal
Analogue uses a whole range of continuous variations to transmit
a signal.
what is a digital signal
Digital signals use only 2 states, on and off.
What is a logic gate
Logic gates are processors that are circuits containing transistors
and other components.
why is damaged insulation a danger of electricity
Damaged insulation: contact with the wire (live wire especially)
due to gap in the insulation causes electric shock which can cause
serious injury or shock.
Why is overheating of cables a danger of electricity
Overheating of cables: when long extension leads are coiled up,
they may overheat. The current warms the wire, but the heat has
less area to escape from a tight bundle. This might cause a fire.
why is damp conditions a danger of electricity
Damp conditions: water can conduct a current, so if electrical
equipment is wet someone might get electrocuted
What is a fuse
A fuse protects a circuit. Thin piece of wire which overheats and melts if current is too high.
It is placed on the live wire before the switch. This prevents overheating and catching fire. A fuse will have a specific current value (e.g. 13A) so when choosing a suitable fuse you must use the one above minimum value but less than maxiumum value
what is a circuit breaker
An automatic switch which if current rises over a specified value, the electromagnet pulls the contacts apart, breaking the circuit. The reset button is to rest everything. It works like a fuse but is better because it can be reset.
What are the benefits of Earthing a Metal Case:
Many electrical appliances, have metal cases, the earth wire creates a safe route for current to flow through, if live wire touches casing
Earth terminal connected to metal casing, so the current goes through earth wire instead of causing an
electric shock.
A strong current surges through earth wire because it has very low resistance
This breaks the fuse and disconnects the appliance.
what happens if a wire is passed across a magnetic field
If a wire is passed across a magnetic field, a small EMF is induced
If the wire forms part of a complete circuit, the EMF makes a current flow and this can be detected using a galvanometer.
The EMF induced in a conductor is proportional to the rate at which the magnetic field lines are cut by the conductor.
What can the induced EMF be increased by
The induced EMF can be increased by: moving the wire faster using a stronger magnet Increasing length of wire in magnetic field, e.g. looping the wire through the field several times.
what can the current and EMF direction be reversed by
The current and EMF direction can be reversed by:
moving the wire in the opposite direction
o turning the magnet round so that the field direction is reversed
What can the current direction be calculated by
Fleming’s right-hand rule
What can the induced EMF (and current) be increased by
moving the magnet faster
using a stronger magnet
increasing the number of turns in the coil
What happens if the magnet is pulled away 2
If the magnet is pulled away, the direction of the induced EMF
(and current) is reversed
what happens when you use South Pole instead of North Pole
Using South pole instead of North pole reverses direction of induced EMF (and current)
What happens if the magnet is held still
there is no EMF
what direction will an induced current flow
An induced current always flows in a direction such that it
opposes the change which produced it
What happens when a magnet is moved towards a coil
When a magnet is moved towards a coil the pole of the coil and magnet next to each other are the same
what happens when the magnet is moved away
When the magnet is moved away the poles are opposite (opposite
poles attract)
What is the pole type controlled by
The pole-type (north or south) is controlled by the direction in
which the current is induced
what is the direction of the current given by
The direction of the current is given by the right-hand grip rule: The fingers point in the conventional current direction and the
thumb gives the North Pole.
What is the oil in an ac generator made of
The oil is made of insulated copper wire and is rotated by turning
the shaft; the slip rings are fixed to the coil and rotate with it.
What are the brushes in the AC generator
The brushes are 2 contacts which rub against the slip rings and
keep the coil connected to the outside part of the circuit, usually
made of carbon.
what happens when the coil is rotated in the AC generator
When the coil is rotated, it cuts magnetic field lines, so an EMF is
generated, which makes a current flow.
When is the current at maximum in an AC generator
The current is maximum when the coil is horizontal since field
lines are being cut at the fastest rate and 0 when the coil is
vertical, since it is cutting NO field lines.
what can the EMF in a AC Generator be increased by
increasing the number of turns on the coil
increasing the area of the coil
using a stronger magnet
rotating the coil faster
How can AC currents be increased
AC currents can be increased or decreased by using a transformer
How do transformers work
Consists of a primary coil, a secondary coil and an iron core.
The iron core gets magnetized by the incoming current and this
magnetism then creates a current in the leaving wire.
The power is the same on both sides (assume= 100% efficiency)
What can you figure out the number of coils and the voltage in a transformer with
𝑶𝒖𝒕𝒑𝒖𝒕 𝒗𝒐𝒍𝒕𝒂𝒈𝒆 / 𝑰𝒏𝒑𝒖𝒕 𝒗𝒐𝒍𝒕𝒂𝒈𝒆 = 𝑻𝒖𝒓𝒏𝒔 𝒐𝒏 𝒐𝒖𝒕𝒑𝒖𝒕 𝒄𝒐𝒊𝒍 / 𝑻𝒖𝒓𝒏𝒔 𝒐𝒏 𝒊𝒏𝒑𝒖𝒕 𝒄𝒐𝒊l
What does a step up and step down transformer do
A step-up transformer increases the voltage and a step-down
transformer decreases it.
What do transformers do
Transformers used to make high voltage AC currents.
why are there transformers
Since transmission cables are many kilometres long they have a
lot of resistance, so a transformer is used to increase the voltage
and decrease the current to decease power lost.
The advantages of high-voltage transmission:
less power lost
thinner, light, and cheaper cables can be used since current is
reduced
what is magnetic effect of current used in
Magnetic effect of current is used in a relay and a circuit breaker
What happens if a current carrying conductor is in a magnetic field
If a current carrying conductor is in a magnetic field, it warps the
field lines.
The field lines from the magnet want to straighten out naturally.
This causes a catapult like action on the wire creating a force.
What happens if you reverse current
If you reverse current, you will reverse direction of force
what happens if you reverse direction of field
If you reverse direction of field, you will reverse direction of force
What is given by flemings left hand rule
The direction of the force, current or magnetic field is given by
Fleming’s left-hand rule
what does a DC motor run on
A DC motor runs on a direct current.
what happens when a current carrying coil is in a magnetic field
When a current-carrying coil is in a magnetic field, it experiences a
turning effect
What is the DC coil made of
The coil is made of insulated copper wire and is free to rotate
between the poles of the magnet.
The commutator (split-ring) is fixed to the coil and rotates with it
What can turning effect be increased by
Increasing the current Using a stronger magnet Increasing length of coils by: Increasing number of coils increasing area of the coil
What can reversing the rotation be done by
- reversing the battery
- reversing the poles
what is background radiation
Background radiation: small amount of radiation around us all
time because of radioactive materials in the environment. It
mainly comes from natural sources such as soil, rocks, air, building
materials, food and drink – and even space.
What does a Geiger-Müller (GM) tube do
The ‘window’ is thin enough for alpha particles to pass through.
If an alpha particle enters the tube, it ionizes the gas inside.
This sets off a high-voltage spark across the gas and a pulse of
current in the circuit.
A beta particle or gamma radiation has the same effect.
It can be connected to a rate meter (tells the counts per seconds)
or a scaler (tells total number of particles or bursts of gamma
radiation)
What is radioactive decay
Radioactive decay: A radioisotope (unstable arrangement of
neutrons and protons) is altered to make a more stable
arrangement.
The parent nucleus becomes a daughter nucleus and a particle
(decay products).
What is alpha decay
An element with a proton number 2 lower and nucleon number 4
lower, and an alpha particle is made (2p + 2n) e.g.
Radium-226 nucleus → Radon-222 + helium-4 nucleus
what is gamma emission.
Gamma emission by itself causes no change in mass number or
atomic number; they just emit energy
Some isotopes do not change in mass or atomic number however
they emit energy as their particles rearrange themselves to
become more stable
What is a half life
Half-life of a radioisotope: is the time taken for half the nuclei
present in any given sample to decay.
Some nuclei are more stable than others.
safety precautions of radiation
Radioactive material is stored in a lead container and locked away
Picked up with tongs, not bare hands
Kept away from the body and not pointed at people
Left out of its container for as short a time as possible
What do atoms consist of
Atoms consist of:
Nucleus: central part of atom made of protons (positively
charged) and neutrons. These two types of particles are called
nucleons. They are bound together by the strong nuclear force.
Electrons: almost mass-less particles which orbit nucleus in shells
Describe RUTHERFORD’S EXPERIMENT
Thin gold foil is bombarded with alpha particles, which are
positively charged.
Most passed straight through, but few were repelled so strongly
that they were bounced back or deflected at large angles.
Rutherford concluded that the atom must be largely empty space,
with its positive charge and most of its mass concentrated in a tiny
nucleus.
What is the nucleus
The nucleus is composed of protons and neutrons. Proton number: number of protons in an atom Nucleon number: the number of nucleons (protons + neutrons) in an atom
what is an isotope and what can it be used for
Isotope: atoms of the same element that have different numbers
of neutrons e.g. Carbon 12 and Carbon 14.
There are non-radioactive isotopes and radio-isotopes.
Radio isotopes are unstable atoms, which break down giving
radiation
Medical use: cancer treatment (radiotherapy) – rays kill cancer
cells using cobalt-60
Industrial use: to check for leaks – radioisotopes (tracers) added
to oil/gas. At leaks radiation is detected using a Geiger counter.
Archaeological use: carbon 14 – used for carbon dating
Define the specific heat capacity of a substance
(thermal) energy required to heat unit mass / 1 kg / 1 g
by unit temperature / 1 °C / 1 K
Density equation
density = mass/volume
how to calculate value for specific heat capacity
Energy divided by mass multiplied by temperature increase/decrease
Define specific latent heat of fusion.
Heat required to change the state of (melt) unit mass (1 kg or 1 g ) of solid
with no change of temperature
(Allow specific example e.g. ice to water)
