Conservation of Energy

Question 1

Different energy stores and their meaning

Answer 1

Thermal - any object - the hotter it is, the more energy it has in this store
Kinetic - anything moving has energy I this store
GPE - anything in a gravitational field
Elastic potential - anything stretched
Magnetic - two magnets that attract and repel each other
Electrostatic - two charges that attract and repel each other
Nuclear - atomic nuclei release energy in nuclear reactions

Question 2

Kinetic energy

Answer 2

-Movement means energy in an object’s kinetic energy store
-Energy transferred when an object speeds up and is transferred away from this store when an object slows down.
-Energy in kinetic store depends on objects mass and speed

Question 3

Kinetic energy formula

Answer 3

Kinetic energy (J) = 1/2 x mass (m) x speed2 (m/s2)

Question 4

Gravitational Potential Energy

Answer 4

• Raised objects store energy in GPE stores
• Lifting an object in gravitational field transfers energy into gpe store
  -The higher the object is lifted, the more energy is transferred in.
  -Amount of energy depends on object’s mass, height and strength of gravitational field.

Question 5

Gravitational Potential Energy formula

Answer 5

Change in GPE = Mass (kg) x Gravitational field strength (N/kg) x change in vertical height (m) or
ΔGPE = m x g x Δh

Question 6

Principle of Conservation of energy

Answer 6

Energy can be stored, transferred between stores, and dissipated, but it can never be created or destroyed

Question 7

What is a Closed system?

Answer 7

• A closed system is a collection of objects that can be treated completely on its own.
  -The total energy of a closed system has no net change
• If a question asks you where the energy of a system increases or decreases it is not a closed system
  -Can turn something into a closed system by increasing the number of things part of it.

Question 8

Different types of energy transfer

Answer 8

Mechanically - a force acting on an object and doing work (e.g pushing, stretching squashing)
Electrically - a charge doing work (e.g charges moving round a circuit)
By heating - energy transferred from a hotter object to a colder object
By radiation - energy transferred by waves

Question 9

Examples of energy transfers - bat hitting ball

Answer 9

Bat has energy in kinetic energy store. Some transferred mechanically to the ball, some transferred mechanically to thermal energy stores of bat and ball. The rest is carried away by sound by radiation

Question 10

Examples of energy transfers - a rock dropped from a cliff

Answer 10

-gravity does work on the rock meaning rock acceelerates towards the ground
-energy is transferred mechanically from the rock’s GPE store to its kinetic energy store.

Question 11

Examples of energy transfers - A car slowing down (without braking)

Answer 11

-Energy from kinetic energy store of car is transferred mechanically due to friction between the tyres and the road.
-then by heating to the thermal energy stores of the car and the road

Question 12

Examples of energy transfers - kettle boiling water

Answer 12

-energy transferred electrically from the socket to the heating pad of kettle
-then by heating to the thermal energy stores of the water.

Question 13

Principle of useful energy

Answer 13

-Energy is only useful when it is transferred from one store to a useful store
total energy input = useful energy output + wasted energy

Question 14

Mechanically wasted energy

Answer 14

-Whenever work is done mechanically, frictional forces have to be overcome (e.g moving parts rubbing together and air resistance)
-The energy needed to overcome these forces is transferred into the thermal energy stores of the object and surroundings
-This energy is not useful

Question 15

How to calculate efficiency

Answer 15

efficiency = useful energy transferred by device / total energy supplied by device

Question 16

Using diagrams to show efficiency

Answer 16

-No device is 100% efficient
-Sankey diagrams are used to show when some are more efficient than others
-The thickness of the arrows represents how much energy is being transferred.
-Wasted energy splits off vertically downwards

Question 17

Ways of reducing energy transferred wasted energy - lubrication

Answer 17

For a objects that are touching with a frictional force, lubricants can be used to reduce the amount of thermal energy transferred mechanically into the objects thermal energy store
-this is because it can flow easily between objects and coat them.

Question 18

Ways of reducing energy transferred wasted energy - Insulation

Answer 18

sw

Question 19

Process of conduction

Answer 19

-When one side of an object, the particles in the hotter part vibrate more and collide with each other
-This transfers energy from their kinetic energy stores to other particles which then vibrate faster and so on

Question 20

Thermal conductivity

Answer 20

-Describes how well a material transfers energy by conduction
-Metals have high thermal conductivity and gases have low thermal conductivity

Question 21

Ways of reducing energy transferred wasted energy - Insulation

Answer 21

-To reduce a buildings ‘rate of cooling’, walls should be thick and have a low thermal conductivity
-Houses have cavity walls and double-glazed windows with an inner and outer wall with an air gap in the middle, reducing amount of energy transferred through walls by conduction.

Question 22

Non - renewable energy sources

Answer 22

-Include coal, oil and natural gas
-Fossil fuels which are burnt to provide energy
-They are finite and will run out one day
-They are very reliable

Question 23

Renewable energy sources

Answer 23

-Include solar, wind, hydro-electricity, Bio fuel and tides
-These will never run out
-Most do damage to the environment but in less nasty ways than non renewables
-Don’t produce as much energy and are unreliable as they depend on the weather

Question 24

Solar Cells

Answer 24

-Often used in remote places (e.g to power road signs and satellites)
-There is no pollution except when making it
- Initial costs are high but there are little to no running costs
-Best in sunny countries but can be used in cloudy countries
-Can’t produce at night and cannot increase production if there is extra demand

Question 25

Wind Power

Answer 25

-No pollution
-Initial costs are high to set up but running costs are minimal
-Need many wind turbines to produce as much power as a coal plant
-Can be noisy and can ‘spoil the view’
-They only work when it is windy so cannot supply reliable energy or respond to high demand

Question 26

Bio fuels

Answer 26

-Created from either plant products or animal dung
-Supposedly carbon neutral but there is a debate on whether it really is
-Fairly reliable as different varieties of crops can be grown all year round
-Cannot respond to immediately energy demands
-The cost to refine Bio fuels is very high
-Large areas of forest have been cleared for Bio fuels resulting in an increase in CO2 and methane emissions

Question 27

Hydro - electricity

Answer 27

-No pollution
-Big impact on environment due to flooding of a valley and loss of habitat for some species.
-It can immediately respond to increased electricity demand by allowing more water through the turbines to generate more electricity
-Reliable energy source

Question 28

Tidal Barrages

Answer 28

-No pollution
-They affect boat access and can spoil the view
-They alter the habitat
-Relies on the tides caused by the Sun and Moon’s gravity so is very reliable
-No fuel costs but initial costs are high

Question 29

Advantages of non-renewable energy sources

Answer 29

-Fossil fuels and nuclear energy are reliable.
-There is enough to meet current demand
-Can quickly respond to changes in demand
-Set up costs of power plants are high but fuel extraction is fairly cheap

Question 30

Disadvantages of non-renewable energy sources

Answer 30

-When coal, oil and gas are released into the atmosphere, it contributes to global warming
-Burning coal and oil releases sulfur oxide which causes acid rain which damages environments
-Nuclear waste produced by nuclear power is very hard to dispose of and takes tens of thousands of years to become safe again