Physics Flashcards
efficiency of a system
output/input * 100 1>ans
Define the specific latent heat of fusion of a substance.
(thermal) energy to change state to melt (solid) per kg / unit mass
describe conduction in terms of particles
free electrons move from atom to atom in lattce
shiny white in terms of radiation
best reflector
show the direction of movement of the wave after it has passed into the shallow water from the deep water
perpendicular to the wave fronts of shallow water 90 degrees
dispersion of light compare red and violet
red diffracts the least whereas violet diffracts the most (within he prism too!!)
A teacher shows his class a polystyrene cup. The cup is made from thick plastic with lots of tiny air bubbles in it. He asks the class why the cup is so good at keeping a hot drink warm
The air is trapped in tiny bubbles so very little convection is possible.
What increases diffraction
the gap size must be the same as the wavelength
longitudinal wave
particles movement is parallel to the direction of energy transfer
constant speed
in equilibrium , forward force = backward force
effect on rarefractions and compressions when lower volume
low amplitude means less displacement and so the rarfraction region particles will increase whereas in compression they will decrease and move further away into rarefraction region.
direction of current
same direction as proton and opposite direction of electron.
is kinetic enerygy scalar or vctor
saclar as the direction does not matter
what happens if there is some air present in the tube of a mercury barometer where there is supposed to be a vaccum
reading of atmospheric pressure decreases
when light enters dense to rare
multiply sin i by refractive index. 1/n = sin i / sin r
in rare medium light moves away from normal.
state what is meant by critical angle
angle of incidence in the denser medium when angle of refraction = 90 degrees n=1/sin i
definition of direction of electric field
direction of force on a positive charge
effect of thermal energy on molecules of water
molecules separate and move apart, intermolecular forces are broken
uses of soft magnets
transformers, electromagnetics, generators,
uses of hard magnets
compass, ammeter, voltmeter, magnetic catches
what is meant by magnetic field
a region in where magnetic materials experience a force
what is meant by rectification
it is the conversion of AC to DC through the use oof diodes
what is limit of proportionality
the point beyond which Hooke’s law is no longer true when stetching a material
hooke’s law
Within the limit of proportionality the extension produced is directly proportional to
the applied force F=ke
k= f/e
define charge
It’s the property of subatomic particle which determines the magnitude of electric or
magnetic force on it.
Units Coulomb (C)
what is meant by electric field
it is a region where a charge experiences a force.
what is meant by electric field strength
It is force per unit positive charge in an electric field”.
electric field strength = force/charge
it is a vector quantity
electric potential difference
it is the work done per unit +ve charge between two points in an electric field
V = J/C
emf
the energy transferred by a cell in driving unit charge around a complete circuit
how to tell which substance has the highest specific heat capcity
lowest mass and lowest temp rise
how to achieve high sensitivity in reflection
long distance apart, and large angle away
what height to use in pressure calculations involving manometer (pressure due to gas)
height= difference in height of two liquid surfaces and then to get pressure add the pressure of gas with atm.
describe molecules arrangement and motion in liquids
molecules close(r) molecules move only small distances (between collisions) or do not move freely molecules move in clusters or slide past each other
describe conduction in terms of electrons
electrons travel a great distance , vibrating and hitting electrons and in this way they transfer energy by hitting distant atoms
what is meant by direction of magnetic field
the direction of force on a north pole
total internal reflection.
the complete reflection of a light ray from an optically dense medium to an optically less dense medium. angle of incidence exceeds critical angle.
State two conditions required for light to be totally internally reflected.
- dense to rare medium
2. angle of incidence must be greater than critical angle
uses of optical fibres
carries infra red radiation for telecommunication, signals, data, messgaes, endoscope light enters
what is background radiation
radiation from the enviornment which is always present. cosmic rays, rocks, soil, sun, nuclear watse
what can thermacouples measure?
liquid nitrogen
define specific latent heat
(thermal) energy (needed) to change state
of unit mass /
what is monochromatic light
same frquency
State and explain why fuses and circuit breakers are installed in electrical circuits connected
to the mains supply
protects components / appliances / circuit / wires / user / mains supply
prevents electrical supply overheating / fires / electrocution / shocks
excess current / power in circuit / wires OR fuse melts / blows OR circuit breaker opens
direction of magnetic field when current is into the page
clockwise
Explain why a source of γ-rays used in this way should not have a half-life shorter or
longer than about 6 hours.
longer half-life
– radioactive substance active in body for a long time
shorter half-life – might be insufficient time for investigation OR it takes time / hours for the tracer to spread round the
body
1
compression
molecules move closer together and pressure is higher than normal.
State two uses for infrared radiation
remote controls
(infrared) sensors / alarms
specific electrical appliances
thermal imaging/ night vision
when handling x rays gamma rays precautions
- distance - limit exposure time - shield against
uses of gamma rays
sterilisation of equipment, medical diagnosis / treatment, thickness control, detecting leaks / cracks,
food preservation
explanation e.g. destroys bacteria, destroys cancer cells, lower amount of radiation detected if thickness too large, radiation
detected at site of leak, destroys microbes in food
definition of speed
rate of change of distance covered per unit time
state newton’s third law
For every action, there is an equal and opposite reaction. They must act on two different bodies.
• EFFECT OF BALANCED FORCES
The body at rest will remain at rest.
The body in uniform motion will continue it.
• EFFECT OF UNBALANCED FORCES
body will accelerate in the direction of resultant force
what is friction and the effects of friction
- an opposing force that slows down motion
- energy is lost in the form of heat or sound
braking distance
It is the distance covered/ travelled after applying breaks. Body is always decelerating during this
factors affecting breaking distance
- speed
- mass of car
- friction between tire and road
what is thinking distance
It is the distance covered/ travelled during reaction time. constant speed
factors that affects thinking distance
- focus of driver
- speed of car
- reflexes of driver
• What makes the body move in a circle in case of
1. Car taking a turn round a corner
friction between tires and road
what makes the moon move in a circle
gravitational pull of earth
what makes an electron move around a nucleus
electrostatic force of attraction
describe the motion of an object travelling on a circular path
- resultant force acts 90 degrees to the motion. whereas the velocity is tangent. the constant resultant force causes the body to constantly change direction allowing it to travel in a circular path. a smaller radius of an object requires a greater force.
state free fall acceleration
10 ms square
Why the acceleration decreases even when the car’s engine is working at full strength?
As the speed increases, air resistance increases too. With the same forward force, increase in air resistance decreases the resultant force. With decrease in resultant force, acceleration decreases
what is the center of gravity
It is the point where all the weight of a body seems to be equal.
how to find the center of gravity of thin lamina
- Hang the lamina to a friction free suspension.
- Hang a plumb line in front of it.
- Mark line behind plumb line.
- Center of gravity lies somewhere on the plumb line.
- Repeat the process from another line.
- The intersection of the two lines will give the center of gravity.
- Repeat the process for confirmation
Transmission of external pressure in fluid
external pressure is equally transmitted in all directions
wave
its the transfer of energy without the net movemet of the particle of the medium
wave front
its an imaginary line perpendicularly joining all the similar points
normal
It is an imaginarly line perpendicular to the surface at the point of incidence.
virtual image
- cannot be captured on a screen
- inverted
red light
greastest wavelenght
violet light
greatest frequency
uses of radio waves
radio and television broadcast
uses of microwaves
microwave oven , satellite communication
UV rays
sterilization, tanning/sun tan, produces fluorecsent in some material
visible light
forms image on retina
x rays
diagnostics purposes, airport security purposes
common properties of em waves
- can travel in vaccum
- same speed
- transverse waves
how is sound produced and propagated?
there is a vibrating body, Due to the vibration particles of the air vibrate in the same direction as that of the transfer of energy, causing compressions and rarefactions in the adjacent layers of air.
factors affecting
- quality
- loudness
- pitch
- waveform
- amplotude
- frequency
uses of an ultrasound
- sonar systems, technique for detecting and determining the distance and direction of underwater objects by acoustic means
- pre natal scanning
- cleaning purposes
when an object is placed beyond 2f the image is…
o Real
o Smaller in size
o Inverted
when object is placed at 2f the image is
o Real
o Same size
o Inverted
when object is placed between 2f and f
o Real
o Larger in size
o Inverted
when the object is placed beyond f
- larger
- virtual
- upright
describe an experiment for refraction
- Place the glass block on a sheet of paper, and carefully draw around the block using a pencil
- Take a ray box and carefully aim the box so that a single ray of light passes through the block
- Using a pencil, mark some points along the path of the ray:Before it reaches the block;Where it hits the block;Where it leaves the block;After it has left the block
- Now remove the block from the paper and, using a ruler and pencil, draw straight lines connecting points: a and b; b and c; c and d. The resulting line will show the path of the ray
- Replace the block within its outline and repeat the above process for a ray striking the block at a different angle
magnifying glass
should always be held close to object, closer to the lens than focal point, virtual
current
rate of flow of charges I = Q/t
potential difference
Energy consumed by unit charge to move across the any two points in the circuit. The energy conversion is from electrical to non-electrical. 1 V = 1 J/C
state ohms law
Current flowing through any wire is directly propotional to potential difference across its ends, provided that temperature remains constant
advantages of connecting lamps in parallel
- the voltage across each bulb will be the same, so every bulb will be equally bright.
- each component is independent of other. …
- Each component can be independently controlled by a switch.,
thermistor
on a graph shows increasing gradient, exponential. as temp increases, current increases and resistances decreases. at low temp resistance is high
LDR
low resistance - bright
high resistance - dark
sensing circuts
In the above circuit, an LDR is used, along with a relay, to control a bulb
When it gets darker, the resistance of the LDR increases
This causes the potential difference across the LDR to increase
When this potential difference increases the current in the coil (part of the relay) will increase
When the current gets large enough the coil will attract the switch, closing it and allowing a current to pass through the right-hand side of the circuit
what fuse rating should one choose
a little above the current or else the fuse will melt and blow even during its normal working
where is the fuse connected and why
it is connected with the live wire in seires so when it blows , the appliance is at 0 volts
where is the earth wire connected
with the metal casing
how does an earth wire work?
In case a fault arises, and metal casing becomes live, a huge amount of current will flow from earth wire to a low resistance path to earth and so the fuse blows up, making us safe.
explain double insulation
The wires are insulated and then the outer casing is made up of an insulator, so there is no need of earth wire
define kWh
The wires are insulated and then the outer casing is made up of an insulator, so there is no need of earth wire
what is a live wire
wire with high voltage charges
neutral wire
Wire with zero voltage charges. It is used to provide potential difference or to complete the circuit
overheating of cables
Passing too much current through too small a wire (or leaving a long length of wire tightly coiled) can lead to the wire overheating. This could cause a fire or melt the insulations, exposing live wires
circuit breakers
Fuses work on the principal of a large current melting the fuse wire. In some cases faults can occur in which the current may not be large enough to melt the fuse but enough to seriously harm the user of the electrical appliance. For protection against faults of this nature a circuit-breaker is used in place of a fuse. circuit breakers dont need to be replaced and could be resetted , are more quick, sensitive and reliable
) Explain, in terms of the momentum of its molecules, why the trapped gas exerts a pressure
on the walls of the tube.
the molecules collid with the walls of the container which cuases a change in momentum and thus causes a force and spreads out on the area
why does evaporation leave a cooling effect
molecules do work against attractive force as they evaporate
more energetic molecules more likely to escape
average energy of remaining molecules decreases
what is the focal length
The distance of the principal focus from the lens is called the focal length, and depends on how curved the lens is
what is the principal focus
point where parrallel rays meet after passing through lens on principal axis
a man outside of the room can hear a low frequency but equally loud sound but cant hear the sound of the high frequency instruments, why is this so?
the low frquency sound has a larger wavelength thus diffraction occurs and the waves bend more.
digital
consists of high or low stages/voltages
analogue
continuously varying voltage
β-particles ionise the air they pass through less strongly than the same number of
α-particles.
- they have less mass
- less energy
- travel faster so less time near to air molecule
what shape helps reduce air resistance
streamlined shape
state the property of linearity in liquid in glass thermometers
liquid expands uniformly with temperature
what increases sensitivity in a thermometer
- thin bore/tube
- smaller bulb
- use liquid with low heat capacity
what increases range in thermometer
- longer tube
- larger glass bulb (volume)
- use liquid which expands less per unit change in temperature
what is the purpose of the iron core in a transformer
links magnetic fields of coils / primary and secondary
• stronger magnetic field in secondary
• better induction
there is a metal casing mounted on the transformer,
state and explain a safety precaution
- earth the metal casing to create and alternative path for electons to flow
- in cases of the live wire touching the metal casing
formula of charge
Q = It
The lead cylinder has a narrow central hole. State and explain the effect of the lead cylinder
beam is narrow, straight and in one direction. radiation in other directions are absorbed.
direction of alpha and beta particles in a magnetic field
use flh rule to find direction of alpha particle (out of/into page) its the same direction as current
- however for beta particle they are fast moving electrons with a lighter mass so they deflect more and in the opposite direction of current/ alpha
can sound travel through a vaccum?
Sound cannot travel through a vacuum because there are no particles to carry the vibrations
where do electrons flow from?
the negative terminal to the positive terminal as they move away from the negative terminal as they are repelled from it
as we increase the angle of the platform why does the object begin to topple
line of action of the centre of mass falls outside the base of the bus. anticlockwise moment is greater than clockwise moment
Where on a manometer is the pressure the greatest
On the lowest U point in between the two ends
Position of circuit breaker
Same as fuse on live wire
A student drops and object from rest. What happens to the velocity and to the acceleration of the ball during the first few seconds after release?
Velocity increases, acceleration decreases
Direction of acceleration and direction velocity in orbital travel
Acceleration is towards the center
And velocity is tangent
A metal ring screens a piece of equipment from a magnetic fields.
Which metal should be used for the ring and why?
Iron, the metal carries the field lines around the equipment
when do we use FRHR and FLHR
right hand : when finding the current being induced
left hand : direction of force
