OCR 21OCR 21stst Century Century Science Science

Unit P3a Revision Unit P3a Revision Sustainable energy

19/04/23

Energy ConsumptionEnergy Consumption

The demand for energy is predicted to rise by a large amount in the next few decades:

What issues will this rise in demand cause?

19/04/23

FuelsFuelsA “fuel” is something that can be burned to release heat and light energy. The main examples are:

Coal, oil and gas are called “fossil fuels”. In other words, they were made from fossils.

19/04/23

Some definitions…Some definitions…A renewable energy source is clearly one that can be _______ (“renew = make again”), e.g. _____, solar power, biogas etc.

A ___________ energy source is one that when it has been used it is gone forever. The main examples are ____, oil and gas (which are called ______ ____, as they are made from fossils), and nuclear fuel, which is non-renewable but NOT a fossil fuel.

Electricity is called a “________ source” because it is converted from other forms – what would these forms be in batteries, wind turbines and solar panels?

Words – non-renewable, coal, fossil fuels, wood, renewed, secondary

19/04/23

PollutionPollutionWhen a fuel is burned the two main waste products are _____ dioxide and ________ dioxide.

Carbon dioxide is a _________ ___ and helps cause _______ _________. This is produced when any fossil fuels are burned.

Sulphur dioxide, when dissolved in ________, causes ______ _____. This is mainly a problem for ___ power stations.

Nuclear power stations do not produce these pollutants because they don’t ____ fossil fuels.

Words – sulphur, coal, global warming, carbon, acid rain, greenhouse gas,

rainwater, burn

19/04/2319/04/23

Using ElectricityUsing ElectricityBasically, electrical devices are used to transfer electrical energy to the environment:

-+

This light bulb will transfer light and heat to the

surroundings.

19/04/23

Energy and PowerEnergy and PowerThe POWER RATING of an appliance is simply how much energy it uses every second.

In other words, 1 Watt = 1 Joule per second

E

TP

E = Energy (in joules)

P = Power (in watts)

T = Time (in seconds)

19/04/23

Some example questionsSome example questions1) What is the power rating of a light bulb that transfers

120 joules of energy in 2 seconds?

2) What is the power of an electric fire that transfers 10,000J of energy in 5 seconds?

3) Rob runs up the stairs in 5 seconds. If he transfers 1,000,000J of energy in this time what is his power rating?

4) How much energy does a 150W light bulb transfer in a) one second, b) one minute?

5) Jonny’s brain needs energy supplied to it at a rate of 40W. How much energy does it need during a 50 minute physics lesson?

6) Lloyd’s brain, being more intelligent, only needs energy at a rate of about 20W. How much energy would his brain use in a normal day?

60W

2KW

150J, 9KJ

120KJ

630MJ

0.2MW

19/04/2319/04/23

PowerPowerPower is “the rate of doing work”. The amount of power being used in an electrical circuit is given by:

P

IVPower = voltage x current

in W in V in A

We can use this equation to analyse power stations:

1) A transformer gives out 10A at a voltage of 50V. What is its power output?

2) An electric fire has a power rating of 2KW. If it runs on a voltage of 230V what is the current?

3) Electricity is transmitted along some lines in the National Grid at 400KV. If the current is 1KA what would be the power through the wire?

500W

8.7A

400MW

19/04/23

The Cost of ElectricityThe Cost of ElectricityElectricity is measured in units called “kilowatt hours” (kWh). The kilowatt hour is a unit of energy but the Joule is too small to count so we use the KWh instead. For example…A 3kW fire left on for 1 hour uses 3kWh of energy

A 1kW toaster left on for 2 hours uses 2kWh

A 0.5kW hoover left on for 4 hours uses __kWh

A 200W TV left on for 5 hours uses __kWh

A 2kW kettle left on for 15 minutes uses __kWh

19/04/23

The Cost of ElectricityThe Cost of ElectricityTo work out how much a device costs we do the following:

Cost of electricity = Power (kW) x time (h) x cost per kWh (p)

For example, if electricity costs 8p per unit calculate the cost of the following…

1) A 2kW fire left on for 3 hours

2) A 0.2kW TV left on for 5 hours

3) A 0.1kW light bulb left on for 10 hours

4) A 0.5kW hoover left on for 1 hour

48p

8p

8p

4p

19/04/23

Reading Electricity MetersReading Electricity Meters

1) How many units of electricity have been used?

2) If 1 unit costs 10p how much has this electricity cost?

1 month later…

19/04/23

The 9 types of energyThe 9 types of energy

Type 3 example sources

Heat

Kinetic (movement)

Nuclear

Sound

Light

Chemical

Electrical

Gravitational potential

Elastic potential

Type 3 example sources

19/04/23

The Laws of PhysicsThe Laws of PhysicsThere are many laws of physics, but one of the most important ones is:

Energy cannot be created or destroyed, it can only be

converted from one form to another

19/04/23

Energy changesEnergy changesTo describe an energy change for a light bulb we need to do 3 steps:

Electricity Light + heat

1) Write down the starting energy:

3) Write down what energy types are given out:

2) Draw an arrow

What are the energy changes for the following…?

1) An electric fire

2) A rock about to drop

3) An arrow about to be fired

19/04/23

Conservation of EnergyConservation of EnergyIn any energy change there is ALWAYS some “waste” energy:

e.g. a light bulb:

In this example HEAT is wasted and it is transferred to the surroundings, becoming very difficult to use.

Electricity Light + heat

Describe the following energy changes and state the “waste” energy or energies:

1) A vacuum cleaner

2) A TV

3) A dynamo/generator

19/04/23EfficiencyEfficiencyEfficiency is a measure of how much USEFUL energy you get out of an object from the energy you put INTO it.For example, consider a TV:

Electrical Energy (200J)

Light (80J)

Sound (40J)

Heat (?)

Efficiency = Useful energy out

Energy in

x100%

19/04/23

Some examples of efficiency…Some examples of efficiency…

1) 5000J of electrical energy are put into a motor. The motor converts this into 100J of movement energy. How efficient is it?

2) A laptop can convert 400J of electrical energy into 240J of light and sound. What is its efficiency? Where does the rest of the energy go?

3) A steam engine is 50% efficient. If it delivers 20,000J of movement energy how much chemical energy was put into it?

0.2 or 20%

0.6 or 60%

40KJ

19/04/23Energy Transfer (“Sankey”) Energy Transfer (“Sankey”) diagramsdiagrams

Consider a light bulb. Let’s say that the bulb runs on 100 watts (100 joules per second) and transfers 20 joules per second into light and the rest into heat. Draw this as a diagram:

100 J/s electrical energy

“Input” energy “Output” energy

80 J/s heat energy (given to

the surroundings)

20 J/s light energy

19/04/23

Example questionsExample questionsConsider a kettle:

1) Work out each energy value.

2) What is the kettle’s efficiency?

Sound energy

Wasted heat

Heat to water

2000 J/s electrical energy

Consider a computer:

150 J/s electrical energy

10 J/s wasted sound

20 J/s wasted heat

Useful light and sound

1) How much energy is converted into useful energy?

2) What is the computer’s efficiency?

19/04/23

Reducing Energy UsageReducing Energy Usage

How can we reduceenergy usage?