GCSE Physics

What is a scalar?

A quantity with magnitude but no direction

Force is a vector. Define a vector.

A quantity with both magnitude and direction

Give 5 vector quantities.

force, velocity, displacement, acceleration, momentum

Give 5 scalar quantities.

speed, distance, mass, temperature, time

What is Newton's third law of motion?

When two objects interact, they exert equal and opposite forces.

What is Newton's first law of motion?

If the forces acting on an object are balanced, the resultant force is 0

Define an elastic object.

An object which regains its shape when forces are removed.

Define a plastic object.

An object which keeps its shape after forces are removed.

What is the relationship between the extension of a spring and the force applied?

Directly proportional

What happens if too much force is applied to a spring?

It exceeds its limit of proportionality

What is the equation for Hooke's Law?

F=ke

Does a stiffer spring have a higher or lower spring constant?

Higher

What is a moment?

The turning effect of a force

What is the equation for a moment?

M=Fd

What is the unit of measurement for a moment?

Nm

What do levers do?

Increase the distance between the pivot and load so less force is required.

What do gears do?

Transmit the rotational effect of a force

What will a force transmitted to a larger gear do?

Cause a larger moment as the distance to the pivot is greater

What speed and turning effect does a low gear give?

Low speed and high turning effect

What speed and turning effect does a high gear give?

High speed and low turning effect

What is the relationship between acceleration and resultant force?

Directly proportional

What is the relationship between acceleration and mass?

Inversely proportional

What is the equation for acceleration?

a = (v-u)/t

What is the equation for constant acceleration?

v²-u²=2as

What is the equation for momentum?

P=mv

What does conservation of momentum mean?

momentum before collision = momentum after

What equation links force and momentum?

F=m(v-u)/t

Define a closed system.

A system in which matter and energy can't enter or leave.

What is the equation for gravitational potential energy?

E=mgh

What is the equation for kinetic energy?

E=1/2 x mv²

What is the formula of power (with work done)?

P=w/t

What is the formula for work done?

W=Fs

What is the rule for resistance in parallel?

1/Rtotal = 1/R1 + 1/R2

What is the rule for resistance in series?

Rtotal = R1 + R2

What is the rule for potential difference in series?

vtotal = v1 + v2

What is the rule for current in series?

i1 = i2

What is the rule for potential difference in parallel?

v1 = v2

What is the rule for current in parallel?

itotal = i1 + i2

What is the formula for power (with potential difference)?

P = IV

What is the equation for potential difference (with energy)?

V = E/Q

What is the equation for specific heat capacity?

Energy change = mass x specific heat capacity x temperature change

What is the equation for current (with charge)?

I = Q/t

What is the equation for charge?

Q = It

What is the equation for power (with resistance)?

P = I^2R

What is the equation for pressure and volume?

PV = constant

What is the equation for density?

P = m/v

What is the equation for latent heat of fusion/vaporisation?

Energy change = mass x latent heat

What is Boyle's law (pressure and volume)?

P1 x V1 = P2 x V2

What is Charles' law (volume and temperature)?

V1/T1 = V2/T2

What is Guy lussacs law (pressure and temperature)?

P1/T1 = P2/T2

What is ohm's law?

If a resistor is kept at a constant temperature, current is directly proportional to the potential difference

What is the relationship between resistance and temperature in a thermistor?

Resistance decreases as temperature increases

What's a diode?

A device that only allows charge to flow in one direction

What is a light-emitting diode (LED)?

A device that emits light when a current passes through the forward direction

What is the relationship between resistance and light in a light-dependent resistor (LDR)?

Resistance decreases as the light falling on it gets brighter

Explain the current-potential difference graph of a filament lamp

It is a curve so current and potential difference aren't directly proportional. The resistance of the filament lamp increases as the current increases. This is because the resistance increases as the temperature increases

What do step-up transformers do?

Make the p.d. across the secondary coil greater than the p.d. across the primary coil. The secondary coil has more turns than its primary coil

What do step-down transformers do?

Make the p.d. across the secondary coil less than the primary coil. The secondary coil has fewer turns than the primary coil

Which wire supplies an alternating current?

Live wire

What voltage does the neutral wire supply?

0 volts

What peaks/troughs does the live wire alternate between and what is the equivalent of a direct current?

+325 V and -325 V (equivalent to a direct current of 230 V)

What are the outer cover of a three-pin plug and the outer casing of sockets made of and why?

A stiff plastic that is a good insulator

What are the pins of a plug made of and why?

Brass as it's a good electrical conductor that is hard and won't rust/oxidise

What is the green and yellow striped wire connected to? (note: this wire is only found in a three-core cable)

Earth pin

What is the brown wire connected to?

Live pin

What is the blue wire connected to?

Neutral pin

What is between the live pin and live wire and what is it for?

The fuse which melts and cut off the current to the live wire if it becomes too big

Why is the earth wire necessary in appliances with metal cases?

Appliances with metal cases must be earthed to prevent the metal casing becoming live if the wire breaks and touches it

Why isn't the earth wire necessary in appliances with plastic cases?

They are double-insulated

What is the relationship between cable thickness and current?

The larger the current to be carried, the thicker the cable needs to be

What is power?

The rate at which energy is transferred

What is the p.d. of the mains supply?

230V

How is a fuse chosen?

So that its current rating is slightly higher than the current of the appliance

Why do resistors heat up?

When charge flows through, energy is transferred to the thermal energy store of the resistor which heats it up. Energy is then transferred to the surroundings

Why do electrical appliances waste energy?

The heating effect of current in wires. Appliances with electric motors also waste energy due to friction

What is the equation for the efficiency of an electrical appliance (energy)?

useful energy transferred/total energy supplied (x 100)

What is the equation for the efficiency of an electrical appliance (power)?

output power/input power (x 100)

What is the frequency of an alternating current in the UK mains supply?

50 Hz

What is the equation for energy (charge and p.d.)?

E = VQ

What is the equation for elastic potential energy of a spring?

E=1/2 x ke²

What does the e in 1/2 ke² mean and what are the units?

Extension of the spring in metres

What happens to wasted energy?

It's dissipated and heats up the surroundings

Give two examples of thermal insulators and why

Fibreglass and wool because they trap air

What factors affect the rate of thermal energy transfer?

Temperature difference across the material, thickness, thermal conductivity

What is the relationship between temperature of an object and how much IR it emits?

The hotter the object, the more IR it emits

What is a perfect black body?

An object that absorbs all radiation and is the best possible emitter of radiation

What does the wavelength which the intensity of IR radiation peaks at depend on?

Temperature

What colour of object releases the most IR radiation?

Matt black

What happens when the ground becomes warm?

It emits longer-wavelength IR radiation

What is specific heat capacity?

The amount of energy required to raise the temperature of 1kg of a substance by 1 degree c

What is the specific heat capacity of water?

4200 J/KgC

How are houses insulated (give 3)?

Fibreglass loft insulation, aluminium foil behind radiators, double glazing

How is electricity generated in most power stations?

Water is heated to produce steam which drives a turbine which is coupled to an electrical generator

What do power stations use as fuel?

Fossil fuels such as oil, coal, or gas

What is a biofuel?

A fuel obtained from living organsims

What are the advantages of biofuels?

They are renewable and carbon-neutral

Give 3 examples of biofuels

Vegetable oil, methane, woodchip

Which nuclear fuels are used in nuclear power stations?

Uranium and plutonium

Give 3 examples of renewable energy sources.

Wind, waves, tides

How do hydroelectric power stations work?

Water is collected in a reservoir at the top of a hill. When it is allowed to flow downhill, it turns turbines that are connected to generators at the bottom of the hill