AQA GCSE Physics - Paper 1

Energy Stores

1. Elastic potential

2. Gravitational potential

3. Thermal

4. Electrostatic

5. Nuclear

6. Chemical

7. Kinetic

8. Magnetic

9. Light

10. Sound

How is energy transferred?

1. Mechanically - force doing work

2. Electrically - work done by moving charges

3. Heating/Radiation - light, sound

How can work be done?

When a current flows or by a force moving an object

Kinetic energy formula

E=1/2mv²
Kinetic energy(J) = 0.5 x mass(kg) x speed²(m/s)

Gravitational potential energy formula

E=mgh
G.P.E(J) = mass(kg) x gravitational field strength (N/kg) x height (m)

What happens when an object falls and there's no air resistance?

Energy lost from the g.p.e store = energy gained in the kinetic energy store

What does air resistance do when acting against falling objects?

It causes some energy to be transferred to other energy stores e.g. the thermal energy stores of the object and the surroundings

Elastic potential energy formula

E=1/2ke²
E.P.E(J) = 0.5 x spring constant(N/m) x extension²(m)

What is SHC?

The amount of energy needed to raise the temperature of 1kg of a substance by 1°C

SHC formula

E=mcθ
Change in thermal energy(J) = mass(kg) x SHC(J/kg/°C) x temperature change(°C)

What is the conservation of energy principle?

Energy can be transferred usefully, or stored or dissipated (wasted energy), but can never be created or destroyed

What is power?

The rate of energy transfer, or the rate of doing work

What is 1W equal to?

1J of energy transferred per second

Power Equation 1

E=Pt
Energy transferred(J) = power(W) x time(s)

Power Equation 2

W=Pt
Work done(J) = power(W) x time(s)

What is conduction?

The process where vibrating particles transfer energy to neighbouring particles
Energy is transferred to thermal stores of the object - this energy is shared across the kinetic energy stores

What is thermal conductivity?

A measure of how quickly energy is transferred through a material via conduction

What is convection?

Where energetic particles move away from hotter to cooler regions
Energy is transferred to the thermal energy stores of the object and is shared across the kinetic stores

What do radiators create?

Convection currents

Convection currents - process

1. Energy is transferred from the radiator to the nearby air particles by conduction

2. The air by the radiator becomes warmer and less dense as the particles move quicker

3. The warm air rises and displaces the cooler air, which is then heated by the radiator

4. The previously heated air transfers energy to the surroundings - the air cools, becomes denser and sinks

What does lubrication do?

Reduce frictional forces

What does insulation do?

Reduce the rate of energy transfer by heating

Thermal insulation techniques

1. Cavity walls - made up of an inner and outer wall with an air gap in the middle - the air gap reduces the amount of energy transferred by conduction through the walls

2. Cavity wall insulators - the air gap is filled with foam also reduces energy transfer by convection in the wall cavity

3. Loft insulation - reduces convection currents being created in lofts

4. Double-glazed windows - air gap between two sheets of glass that prevent energy transfer by conduction through the windows

5. Draught excluders - reduce energy transfers by convection around doors and windows

How do you improve efficiency?

1. Lubrication

2. Insulation

3. Making objects more streamlined

Efficiency - energy transfer equation

Useful output energy transfer divided by total input energy transfer

Efficiency - power equation

Useful power output divided by total power input

Is any device 100% efficienct?

No

Where is wasted energy usually transferred?

Thermal energy stores

How do thick walls prevent energy losses through heating?

They're made from a material with a low thermal conductivity - the thicker the walls, the lower the thermal conductivity, the slower the rate of energy transfer

What objects are usually 100% efficient?

Electric heaters - all the energy in the electrostatic energy stores is transferred to useful thermal energy stores

Fossil fuels (coal, oil, natural gas)

Non-renewable
Cause acid rain
Cause global warming
Reliable currently - they are finite, so they will run out eventually
Coal mining ruins the landscape
Oil spillages cause serious environmental problems

Energy resources used for transport

Petrol and diesel from oil - non-renewable
Coal (steam trains) - non-renewable
Bio-fuels - renewable

Energy resources used for heating

Natural gas - non-renewable
Coal - non-renewable
Electric heaters - non-renewable
Geothermal - renewable
Solar water heaters - renewable
Bio-fuels - renewable

Wind Power

Renewable
Doesn't cause global warming
Doesn't cause acid rain
No pollution
No permanent damage to the landscape
Free - initial costs are high
Very noisy
Spoil the view
Not always reliable

Solar Power

Renewable
Doesn't cause acid rain
Doesn't cause global warming
No pollution
Free - solar panels are expensive though
Not always reliable

Geothermal Power

Renewable
Doesn't cause acid rain
Doesn't cause global warming
Free
Very little damage to the environment
Not very reliable - can only happen in certain places and there aren't very many of them

Hydroelectric Power

Renewable
Reliable
Doesn't cause acid rain
Doesn't cause global warming
No pollution
Provides an immediate response to high demand
Free - initial cost is high
Big impact on environment and possible loss of habitat

Wave Power

Renewable
Doesn't cause acid rain
Doesn't cause global warming
Free - initial costs are high
Not always reliable - waves die out when the wind drops
Disturbs the seabed and habitats of marine wildlife
Spoils the view
Hazard to boats

Tidal Power

Renewable
Reliable
Doesn't cause acid rain
Doesn't cause global warming
No pollution
Free - initial costs are moderately high
Spoils the view
Alters the habitats of wildlife

Bio-fuels

Renewable
Reliable
Doesn't cause acid rain
Carbon neutral
Free
Can cause global warming
Loss of natural habitat from destruction of forests
Cannot respond to immediate energy demands

Nuclear Power (Uranium or Plutonium)

Doesn't cause acid rain
Doesn't cause global warming
Reliable currently - finite
Non-renewable
High decommissioning costs
Produces radioactive waste - no other pollution
Nuclear waste is dangerous and hard to dispose of

Investigating Specific Heat Capacities - Method

1. Measure the mass of a block with two holes in it, then wrap it in an insulating layer (e.g. newspaper) to reduce the energy transferred from the block to the surroundings. Insert the thermometer into one hole and the heater into another

2. Measure the initial temperature of the block & set the potential difference of the power supply to be 10V. Turn on the power supply & start a stopwatch

3. When you turn on the power, the current in the circuit does work on the heater, transferring energy electrically from the power supply to the heater's thermal energy stores - this energy is then transferred to the material's thermal energy store by heating, causing its temperature to increase

4. As the block heats up, take readings of the temperature and current every minute for 10 minutes - the current shouldn't change

5. Turn off the power supply. Use the measurements of the current & the p.d. to calculate the power supplied to the heater, thus calculating how much energy has been transferred to the heater at the time of each temperature reading

6. If you assume all the energy supplied to the heater has been transferred to the block, you can plot a graph of energy transferred to the thermal energy store of the block against temperature

Investigating the Effectiveness of Materials as Thermal Insulators - Method

1. Boil water in a kettle. Pour some of the water into a sealable container to a safe level. Measure the mass of water in the container

2. Use a thermometer to measure the initial temperature of the water

3. Seal the container & leave it for 5 minutes. Measure this time using a stopwatch

4. Remove the lid & measure the final temperature of the water

5. Pour away the water & allow the container to cool to room temperature

6. Repeat this experiment, but wrap the container in a different material once it has been sealed. Ensure the mass of water is the same and so is the initial temperature each time

What is a closed system?

A system where neither matter nor energy can enter or leave

Why did electricity use in the 20th century increase?

1. The population grew

2. People began to use electricity for more & more things

Why did electricity use in the 21st century decrease?

1. Appliances are becoming more efficient

2. We're more careful with energy use in our homes

Why are we trying to increase our use of renewable energy resources?

1. Burning fossil fuels is damaging to the environment

2. Non-renewables will run out one day

3. Pressure from other countries & the public has led to targets being set e.g the UK aims to use renewable resources to provide 15% of the total yearly energy by 2020

What has pressure from the public & other countries led to?

Pressure being put on energy providers to build new power plants that use renewable resources to ensure that they don't lose business & money

What is the use of renewables limited by?

1. Reliability - since some energy resources aren't that reliable, a combination of different power plants would have to be used - expensive

2. Money - building new power plants costs money, the cost of switching to renewable power will have to be paid & some people don't want to or can't afford to pay

3. Politics - companies and governments can't force people to change their behaviour

What happens when a system changes?

Energy is transferred - it can be transferred into/away from the system, between different objects in the system or between different types of energy stores

Why are wind turbines unlikely to be able to power everything in the UK?

1. Large numbers of turbines would need to be built - takes up space & is expensive

2. Not always windy - the same amount of electrical power won't be produced every day

What is electric current?

The flow of electrical charge

What is electric current measured in?

Amps

What is potential difference?

Voltage - it pushes the electric charge around the circuit

What is potential difference measured in?

Volts

What is resistance?

Anything that slows the flow down

What is resistance measured in?

Ohms

The greater the resistance...

...the smaller the current that flows

What is the formula for charge?

Charge (coulombs) = current (amps) x time (seconds) Q=It

What is the formula for Pd?

Potential difference (volts) = Current (amps) x Resistance (ohms) V=IR

The longer the wire...

...the greater the resistance

Is the ammeter placed in series or parallel?

Series

Is the voltmeter placed in series or parallel?

Parallel

Do Ohmic Conductors have a constant resistance?

Yes - at a constant temperature, the current is directly proportional to the potential difference

What does resistance change in?

Diodes and filament lamps

Why does resistance increase with temperature in a filament lamp?

When the electrical charge flows through the lamp, it transfers some energy to the thermal energy stores of the filament which is designed to heat up. Therefore, the resistance, temperature and current all increase
Resistance is directly proportional to temperature

What is an LDR?

Light Dependent Resistor - a resistant dependent on the intensity of light
In bright light, the resistance decreases
In darkness, the resistance is highest

What is a thermistor?

A temperature dependent resistor
In hot conditions, the resistance decreases
In cold conditions, the resistance increases

What happens to Pd in a series circuit?

It's shared between all the components

What happens to current in a series circuit?

The current is the same in all components

What happens to resistance in a series circuit?

The total resistance is the sum of all the resistances

What happens to Pd in a parallel circuit?

The Pd is the same in all components

What happens to current in a parallel circuit?

The current is shared between the components, therefore the total current is found by adding up the currents of all the components

What happens to resistance in a parallel circuit?

If you have two resistors parallel, their total resistance is less than the resistance of the smallest of the two resistors

Mains supply is...

AC - Alternating current

Battery supply is...

DC - Direct Current

Alternating Current

The current is constantly changing direction
Alternating currents are produced by alternating voltages in which the positive and negative ends keep alternating

UK Mains Supply Voltage

230V

UK Frequency of AC

50Hz (hertz)

Direct Current

Current is always flowing in the same direction
Created by a direct voltage

Live Wire

Brown colour
Bottom right of the three pin plug
Provides the alternating pd from the mains supply - 230V
Current flows in through this wire

Neutral Wire

Blue colour
Bottom left of the three pin plug
Completes the circuit and carries away current
Electricity flows out through this wire
Around 0V

Earth Wire

Green and yellow colour
Middle of the three pin plug
Protects the wiring
Stops the casing from becoming live
Doesn't usually carry a current - only when there's a fault
Around 0V

Equation - Energy transferred 1

Energy transferred (J) = Power (W) x Time (s) E=Pt

A 600W microwave is used for 5 minutes. How long (in minutes) would a 750W microwave take to do the same amount of work

1. 600 x (5 x 60) = 180,000J or 180kJ

2. 180,000J = 750W x t

3. t = 180,000J/750W

4. t = 240s = 4 minutes

The lower the power rating...

...The less electricity an appliance uses in a given time, therefore it is cheaper to run

Equation - Energy Transferred 2

Energy transferred (J) = Charge flow (C) x Potential difference (V) E=QV

The motor in an electric toothbrush is attached to a 3V battery. 140C of charge passes through the circuit as it is used. Calculate the energy transferred

1. E=QV

2. E= 140C x 3V

3. E = 420J

Equation - Power 1

Power (W) = Potential difference (V) x Current (A) P=VI

Equation - Power 2

P=I²xR
Power = current² x resistance

A 1.0kW hair dryer is connected to a 230V supply. Calculate the current through the hair dryer. Give your answer to two significant figures

I=P/V
I= 1000/230
I=4.3A

What is the National Grid?

A giant system of cables and transformers that covers the UK and connects power stations to consumers

When does demand for electricity increase?

When it starts to get dark or cold outside
When people get up in the morning
When people come home from school or work

What is the problem with a high current?

You lose loads of energy as the wires heat up and energy is transferred to the thermal energy stores of the surroundings

What's the cheaper way of transmitting power?

High potential difference and low current - decreases the energy lost by heating the wire and the surroundings

How is static electricity caused?

Friction - when two things rub against each other, electrons from one will rub off on to the other
One material will have a positive static charge (e.g. acetate) and the other will have a negative static charge (e.g. polythene)

What subatomic particle moves?

Electrons
Positive charges never move - a positive charge is achieved when electrons move away

What increases with a build up of electric charge?

The potential difference between the object and the earth

What is the spark?

When the electrons jump across the gap between the charged particle and the earth if the potential difference becomes too large

How big is the gap for the spark to happen?

Usually fairly small (lightning is an exception)