Physics Flashcards
How does an insulator become charged?
Electrons are transferred from one material to another by friction
What is charging caused by?
A loss or gain of electrons
What is important to remember about like charges?
They will repel
What is important to remember about unlike charges?
They attract
What happens when an appliance short circuits?
The live wire of an appliance touches the neutral wire
What is an earth wire used for?
If there is a fault in the circuit, the earth wire carries the charge into the ground
Circuit symbol for a cell
A longer vertical line parallel to a shorter parallel line on the right
Circuit symbol for a battery
Multiple cells joined together
Circuit symbol for lamp
Circle with a cross inside
Circuit symbol for a resistor
A clear rectangle
Circuit symbol for variable resistor
A rectangle with a diagonal arrow pointing from bottom left to top right
Circuit symbol for ammeter
Circle with an A inside
Circuit symbol for voltmeter
Circle with a V inside
Circuit symbol for switch
Two circles connected by a straight line
Circuit symbol for diode
A circle with a triangle and straight line inside
What is the difference between direct and alternating current?
An alternating current repeatedly reverses direction
What is the difference between conductors and insulators?
A conductor allows energy to pass through it whereas an insulator doesn’t
Examples of conductors
Copper and aluminium
Examples of insulators
Plastics and rubber
Equation for current
Charge flow / time
What are voltmeters used for?
Measures the potential difference across a component
Equation for resistance
Potential difference / current
What does the V-I graph for a fixed resistor look like?
A diagonal line from bottom left to top right directly through the origin
What does the V-I graph for a filament lamp look like?
A curve from bottom left to top right passing directly through the origin
Properties of LDRs
Resistance decreases with light intensity
Properties of ideal diodes
Allows the current to flow in one direction only
What are the rules for current in a series circuit?
The same current passes through each component
What are the rules for voltage in a series circuit?
The total potential difference is shared between the components
How to calculate the total resistance in a series circuit?
Add the resistances of each component
What are the rules for current in a parallel circuit?
The total current is the sum of the currents passing through the branches
What are the rule for potential difference in a parallel circuit?
The potential difference across each component is equal
Why is the total resistance in a parallel circuit less than that of any individual resistor?
The potential difference remains the same. Adding a resistor increases the current entering the system
Resistance = p.d./i so resistance decreases
Equation for voltage
Energy transferred / charge flow
What are the two equations for power?
Current x voltage
Current^2 x resistance
What does energy transferred equal?
Power x time
What is the north pole of a magnet?
The end of the magnet that will always point north
What is the south pole of the magnet?
The end of the magnet that will always point south
What is attraction?
The force between two unlike poles
What is repulsion?
The force between two like poles
Describe the magnetic field around a magnet
Lines point in a direction away from the north pole towards the south, the magnetic field is more concentrated at the poles
What is the difference between soft and hard magnets?
Hard magnetic retain their magnetism and are difficult to demagnetize, soft magnetic materials are easy to demagnetize
Describe induced magnetism
An unmagnetized material can be magnetized by placing it inside a magnetic field
What is the difference between permanent and electromagnetism?
A permanent magnet retains its magnetism over a long period of time, whereas electromagnets can be magnetised and demagnetised
How to increase the magnetic field of a solenoid
Increase the strength of the current
Can reverse its direction by reversing the direction of the current
Characteristics of solids
Particles are tightly packed
Characteristics of liquids
Particles are packed together but less tightly than solids. Liquids take on the shape of their container
Characteristics of gases
Particles are held together loosely
What is the effect of temperature on particles?
The particles move faster with more kinetic energy and collide more frequently
What is the effect of pressure on particles?
The particles are held closer together so collide more often
At constant temperature, what will both pressure and volume be?
Constant
What is melting point?
The temperature at which a solid melts
What is boiling point?
The temperature at which a liquid turns into a gas
What is the latent heat of fusion?
The amount of heat energy required to change 1g of a substance from the solid to liquid state without changing its temperature
What is latent heat of vaporisation?
The amount of energy required to change 1g of a substance from the liquid to gaseous state without changing its temperature
Equation for density
Mass / volume
What happens to density as you move from solid to gas?
It decreases
How do you determine density experimentally?
The amount of water displaced when an object is placed in a body of water is its volume. Use this and its mass to calculate density
Equation for pressure
Force / area
Equation for hydrostatic pressure
h x p x g
h = Height of column
p = density of liquid
g = acceleration of gravity
Equation for hydrostatic pressure
h x p x g
h = Height of column
p = density of liquid
g = acceleration of gravity
What are thermal conductors?
Materials that allow heat to travel through them
What are thermal insulators?
Materials that don’t allow heat to travel through them
Examples of thermal conductors
Steel, copper, aluminium
Examples of thermal insulators
Plastic, wool, foam
What factors affect the rate of conduction?
Temperature difference across the material
Thickness of material
Thermal conductivity of material
What impact does temperature have on the density of fluid?
Increasing temperature = increased volume = decreased density
What will happen to a wire carrying a current in a magnetic field?
It will experience a force
How to remember the factors affecting the direction of a force on a wire?
The left hand rule - first finger = field
- thumb = movement
- second finger = current
What are the factors affecting the direction of a force on a wire in a magnetic field?
Magnetic field and current
What are the factors affecting the magnitude of a force on a wire in a magnetic field?
Size of current, strength of magnet
How do you calculate the force on a wire?
Force = magnetic flux density x current x length
How is a dc motor constructed?
A coil rotates inside a magnetic field
An electric current is induced
The output comes via split ring output
As the coil turns, the split-ring commutator reconnects The coil the opposite way around each the circuit each half turn
This means that the wire will only be connected to one half of the output
Therefore, the current flows in one direction only
What are electromagnets used in
Cranes, motors, doorbells
When will a voltage be induced in a wire?
When a wire cuts a magnetic field
How does an ac generator work?
The movement of the bar magnet induces a p.d. in the coil
This p.d. creates a current because the coil is part of a complete circuit
When will the outcome of the generator be highest?
When the plane of the coil is parallel to the magnetic field
Use a magnet with a strong magnetic field
More turns on the coil of wire
What will the graph of an ac generator look like?
A sin graph
What is a step up transformer?
Increase the size of an alternating potential difference
What is a step down transformer?
Decreases the size of an alternating potential difference
What is the voltage ratio for transformers?
Coils on 1 / coils on 2 = voltage on 1 / voltage of 2
What is important about a transformer that is 100% efficient?
It is the total transfer of electrical power - VpIp = VsIs
Why is it important that a transformer has a high voltage?
Reduces energy lost in resistance
What is a scalar quantity?
Has only magnitude
What is a vector quantity?
Has both magnitude and direction
What is the difference between speed and velocity?
Speed is a scalar quantity, velocity is a vector
What is the difference between distance and displacement?
Distance is a scalar quantity, displacement is a vector
Equation for speed
Distance / time
Equation for velocity
Change in displacement / time
Equation for acceleration
Change in velocity / time
What is the gradient of a distance-time graph?
Speed
What is the gradient of a displacement-time graph?
Velocity
What is the gradient of a speed-time graph?
Acceleration
What is the area under a speed-time graph?
Distance travelled
What is the gradient of a velocity-time graph?
Acceleration
What is the area under a velocity-time graph?
Displacement
What does average speed equal?
Total displacement / total time
What is the equation of motion?
v^2 - u^2 = 2as
What are the different forces?
Weight, normal contact, drag, friction, magnetic, electrostatic, thrust, upthrust, tension and lift
What does work equal?
Force x distance
What is work done?
Transfer of energy
What does gravitational potential energy equal?
Mass x gravitational field strength x height
What does kinetic energy equal?
.5 x mass x velocity^2
What is the law of the conservation of energy?
Energy can’t be created or destroyed, only transformed from one form to another
What is wasted energy?
Energy that isn’t used in the way that it was intended to
Equation for percentage efficiency
(useful output/total output) x 100
What does frequency equal?
1 / period
What does wave speed equal?
Distance / time or frequency x wavelength
Where are neutrons and protons found?
The nucleus
Where are electrons found?
Orbitals
Charge and mass of neutron
0, 1
Charge and mass of proton
1, 1
Charge and mass of electron
Very small, 1/2000
What is ionisation caused by?
Gain/loss of electrons
Where do emissions arise from?
An unstable nucleus
What is an atom’s half life?
The time taken for half of the unstable nuclei to decay
Properties of diodes
No resistance, only allows the current to flow in one direction
Properties of thermistors
Resistance decreases with increasing temperature
Properties of LDRs
Resistance decreases with increasing light intensity
What does the magnetic field pattern around a solenoid look like?
Each field line is a complete loop which bends from one side of the solenoid to the other
What is the resultant force?
The effect of multiple forces on an object written as a single force
What does the gradient of a force-extension graph equal before the limit of proportionality is reached?
The spring constant
What is the elastic limit?
The point at which a spring has been so stretched so much it won’t return to its original shape
What is Hooke’s law?
The force needed to stretch a spring is directly proportional to the extension of the spring from its natural length
Equation for Hooke’s law
Force = k x Δl
Equation for elastic energy
.5 x k x x^2
What is Newton’s first law?
A body will remain at rest or travel uniformly unless acted on by a resultant external forc
What property can change an object’s inertia?
Mass
What is Newton’s second law?
Force = mass x acceleration
What is Newton’s third law?
Two objects exert equal and opposite forces on eachother
Equation for momentum
Mass x velocity
Equation for force when using momentum
Force = change in momentum
What is the law of the conservation of momentum?
The momentum before a collision = the momentum after
What is the value of gravitational field strength?
10 N/kg
Equation for weight
Weight = mass x gravitational field strength
What is the difference between mass and weight?
Weight is the force exerted by gravity on an object
What is terminal velocity?
The velocity reached on an object when the drag force is equal and opposite to the force making it move
What factors affect terminal velocity?
The object’s mass and surface area
Gravitational field strength
What is free-falling acceleration
An object falling purely under the force of gravity
What will happen to an object’s temperature when energy is transferred to/from it?
It will increaese/decrease
Equation for specific heat capacity
Thermal energy / (mass x Δtemperature)
What electromagnetic waves are involved in thermal radiation?
Infrared
What material is good at absorbing radiation?
A light coloured/shiny one
What factors affect the rate of emission/absorption?
The surface area, volume and material of an object
What is the equation for specific latent heat?
Energy / mass
Equation for specific heat capacity
m x c x Δt
What happens when waves are reflected at a surface?
The reflected ray is at the same angle as the incident ray
What happens when waves refract at a boundary?
The waves change both speed and direction
What effect does reflection have on frequency, wavelength and direction?
Frequency: same
Wavelength: same
Direction: same
What effect does refraction have on frequency, wavelength and direction?
Frequency: same
Wavelength: decreases
Direction: bends towards normal
What is the doppler effect?
The change in distance between causer and observer causes a change in frequency and wavelength
What does the angle of incidence equal?
The angle of reflection
What is nuclide notation?
A(X) Z Contains Z protons and A-Z neutrons Atomic mass = A Charge = +Ze
How far can alpha radiation penetrate?
It is blocked by paper
How far can beta radiation penetrate?
Blocked by aluminium foil
How far can gamma radiation penetrate?
Blocked by thick lead sheet
Rank the three types of radiation from highest ionising power to weakest
Alpha, beta, gamma
Where does background radiation come from?
Radon gas
What is an alpha particle made from?
2 protons and 2 neutrons
What is a beta particle made from?
An electron
What is gamma radiation made from?
Waves
What effect does alpha radiation have on atomic number?
Its atomic number decreases by 2
Its mass number decreases by 4
What effect does beta radiation have on atomic number?
The atomic number increases by 1
What effect does gamma radiation have on atomic number?
None
Which types of radiation can be deflected by electric fields?
Alpha and beta radiation
Give two properties of electromagnetic waves
They are transverse waves and travel at the speed of light in a vacuum
What are the seven components of the spectrum?
Radio waves, microwaves, IR, visible light, ultraviolet, x-rays, gamma rays
Give the wavelengths and frequencies of the component parts of the electromagnetic spectrum
Radio waves: 10^3 and 10^4 Microwaves: 10^-2 and 10^8 IR: 10^-5 and 10^12 Visible light: 10^-6 Ultraviolet: 10^-8, 10^15 X-rays: 10^-10 and 10^18 Gamma rays: 10^-12 and 10^20
What are produced by reflections?
Echoes
What is the range of human hearing?
20Hz to 20kHz
How is volume related to amplitude?
Volume is proportional to amplitude
How is pitch related to frequency?
They are directly proportional
How do ultrasounds measure internal boundaries?
When there is a boundary, some ultrasound is reflected back. The time taken is recorded and this is used to work out how far the boundary is
How are ultrasounds used for medical imaging?
Wherever there is a boundary, some of the wave is reflected back and detected
The timing and distribution of these echoes are recorded and turned into an image
Why is a medium needed for sound?
Sound molecules vibrate and pass the impulse between one another; this can’t happen in a vacuum
How are sound waves produced?
An object vibrates and transfers this energy to another medium
What is the amplitude?
The height of a wave
What is the frequency?
The number of oscillations in a given time
What is the wavelength?
The difference between crests in successive waves
What is the period?
The time taken for one complete wave
What is the peak?
The highest point on a wave
What is the trough?
The lowest point on a wave
What is a compression?
The wave is compressed
What is a rarefaction?
The wave is stretched
What is important to remember about waves?
They transfer energy without the movement of matter
What are transverse waves?
The oscillations are perpendicular to the direction of energy transfer
What are longitudinal waves?
The oscillations are parallel to the direction of energy transfer
Examples of transverse waves
Electromagnetic waves
Examples of longitudinal waves
Sound waves
What properties make a good electrical conductor?
Low first ionisation energy, simple material structure
How to calculate total resistance in parallel?
1/R1 + 1/R2 + 1/R3 etc
