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Physics > Energy > Flashcards

Energy Flashcards

1
Q

When did the concept of energy emerge?

A

19th century

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2
Q

Why did the concept of energy start?

A

To explain the work output of steam engines and then generalised to understand other heat engines. Key tool to understand chemical reactions and biological systems

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3
Q

What is a system?

A

An object or group of objects

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4
Q

Name the 8 energy stores

A 
Thermal
Kinetic
Gravitational potential
Elastic potential
Chemical
Magnetic
Electrostatic
Nuclear
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5
Q

How is energy transferred?

A

Mechanically(by a force doing work), electrically (work done by moving charges), by heating or by radiation

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6
Q

What happens when a system changes?

A

energy is transferred. Can be transferred into or away from system, between different objects in system or between different types of energy stores

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7
Q

What are closed systems?

A

Systems where neither matter nor energy can enter or leave. The net change in the total energy of a closed system is alway 0

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8
Q

Explain boiling water in a kettle

A

Think of the water as a system. Energy gets transferred to the water by heating, into the waters thermal energy store. (causes temp to rise)

Or

Energy is transferred electrically to the thermal energy store of the kettles heating element, transfers energy by heating to the waters thermal energy store

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9
Q

What is work done?

A

another way of saying energy transferred

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10
Q

When can work be done?

A

When current flows or by a force moving an object

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11
Q

Explain the energy transfer when a person throws a ball upwards

A

Energy transfer from the chemical energy stores of the person’s arm to the kinetic energy store of the ball and arm

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12
Q

Explain the energy transfer in a ball dropping

A

Gravitational force does work

Energy transfer from gravitational potential energy stores go kinetic energy store

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13
Q

Explain the energy transfer in a car slowing down

A

Friction between cars brake and wheels does work

Energy transfer from wheel’s kinetic energy store to thermal energy store of surroundings.

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14
Q

Explain the energy transfer between a car and a stationary object

A

Normal contact force between the car and object does work, energy transferred from car’s kinetic energy store to other energy stores e.g. elastic potential and thermal energy stores of object and car body. Some energy might be transferred away by sound waves

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15
Q

What is the equation for kinetic energy?

A

Ek = 1/2mv2

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16
Q

What is the equation for gravitational potential energy?

A

Ep= mgh

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17
Q

Equation for elastic potential energy

A

Ee = 1/2ke2

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18
Q

What is specific heat capacity?

A

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

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19
Q

Equation for specific heat capacity

A

Change in thermal energy = mass x specific heat capacity x temperature change

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20
Q

How to investigate specific heat capacities

A

1) need a block of metal with 2 holes in it for heater and thermometer
2) measure mass of block, wrap in insulating layer to reduce energy transferred from block to surroundings. Insert thermometer and heater
3)Measure initial temperature of block and set potential difference of power supply to 10V. Turn on power supply and start stop watch
4) When you turn power on, current in circuit does work on heater, transferring energy electrically from power supply to heaters thermal energy store. Energy is then transferred to materials thermal energy store by heating, causing materials temp to increase
5) A’s block heats up, take reading of temp and current, I, every minute for 10 minutes. Should fine current through circuit doesn’t change
6) When collected enough readings, turn power supply off, can calculate the power supplies to heater. P=VI. Can use this to calculate how much energy has been transferred to heater at time of each temp reading using E=Pt
7) Assume all energy supplied to heater had been transferred to block, can plot graph of energy transferred to thermal energy store of block against temp.
8) Find gradient. Temp change/ change in thermal energy
So specific heat capacity of material of block is 1/(gradient x mass)

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21
Q

Define Power

A

The rate at which energy is transferred or the rate at which work is done

22
Q

Equation for power

A

Energy transferred/ time

Work done/ time

23
Q

An energy transfer of 1 joule per second is equal to

A

a power of 1 watt

24
Q

Example of power

A

2 cars identical in every way apart from power of their engines
Race the same distance along straight race track. Car with more powerful engine will reach finish line faster than the other car. Transfer same amount of energy over less time

25
Q

Conservation of energy

A

Energy can be transferred usefully, stored or dissipated, but cannot be created or destroyed

26
Q

Example of energy transfer in a closed system

A

Cold spoon dropped into insulated flask of hot soup, then sealed. Can assume the flask is a perfect thermal insulated so spook and soup form closed system. Energy transferred from thermal energy store of soup to useless thermal energy store of spoon. Energy transfers occur within system, no energy left- net change in energy is 0

27
Q

Example of wasted energy

A

Mobile phone is a system. When you use phone, energy is usefully transferred from chemical energy store if battery in phone. But some energy is dissipated in this transfer to thermal energy store of the phone

28
Q

The higher the _______ ________ of a material the higher the rate of ______ _______ by conduction across the material

A

1) Thermal conductivity

2) Energy transfer

29
Q

How does lubrication reduce frictional forces?

A

Frictional force causes energy to be dissipated
Lubricants can reduce friction between objects surfaces when they move. Lubricants usually liquids so can flow easily between objects and coat them

30
Q

How does insulation reduce rate of energy transfer by heating?

A

Thick walls made from material with low thermal conductivity
Thick the walls and the lower their thermal conductivity, slower the rate of energy transfer will b
Examples:
Cavity walls: Inner and outer wall with air gap between, rescues energy transfer
Loft insulation: reduce convection currents
Double glazed windows- air gap between 2 sheets of glass to prevent energy transfer by conduction
Draught excluders reduce energy transfer by convection

31
Q

How can you investigate effectiveness of materials as thermal insulators?

Insulation required practical

A

Boil water in kettle. Pour water into sealable container. Measure mass of water
Use thermometer to measure initial temp
Seal container, leave for 5 mins. Use stopwatch
Remove lid and measure temp
Pour away water and allow container to cool to room temp
Repeat experiment wrapping different materials around container. Use same mass of water and same initial temp
Lower temp difference, better the thermal insulator. Bubble wrap and cotton wool
Investigate best thickness too

32
Q

Equation for energy efficiency

A

Useful output energy transfer/ total input energy transfer

Useful power output/total power input

33
Q

How can you improve efficiency of energy transfers?

A

Insulating objects
Lubricating objects
Make them more streamline

34
Q

What are the main energy resources available for use on Earth?

A 
Fossil fuels(Coal, Oil, Gas)
Nuclear fuel
Biofuel
Wind
Hydro-electricity
Geothermal 
Tides
Sun
Water waves
35
Q

What is a renewable energy resource?

A

One that is being replenished as it is used

36
Q

Examples of uses of energy resources

A

Transport
Electricity generation
Heating

37
Q

Example of non renewable energy resources

A

Coal
Oil
(Natural) Gas

38
Q

Example of renewable energy resources

A 
Sun
Wind
Water waves
Hydro electricity
Bio fuel
Tides
Geothermal
39
Q

How can energy resources be used for transport?

A

Petrol & diesel
powered vehicles use fuel creates from oil
Coal is used in some old fashioned steam trains to boil water to produce steam

Can run on pure bio fuels or a mix of bio fuels and petrol or diesel

40
Q

How can energy resources be used for heating?

A

Natural gas is most widely used for heating homes in UK. Gas heats water, pumped into radiators
Coal used in fireplaces
Electric heaters use electricity

Geothermal heat pump uses geothermal energy
Solar water heaters use sun
Burning bio fuel

41
Q

Properties of non renewable energy resources

A

All run out one day
Damage environment
Provide most of our energy

42
Q

Properties of renewable energy resources

A

Never run out
Most do some damage to environment but not as much as non renewable
Don’t provide as much energy and can be unreliable depending on weather

43
Q

Wind power

A

wind turbines, no pollution, not pretty, can be noisy
Stop working when wind stops or too strong, can’t increase supply when extra demand. Initial costs high, no fuel costs and minimal running cost. No permanent damage to landscape

44
Q

Solar cells

A

Expensive, no environmental damage
Sunlight
no pollution
No reliable if you live in a cloudy country
Can’t increase power output when extra demand

45
Q

Geothermal power

A

energy in underground thermal energy stores
Possible in volcanic areas, hot rocks . Source is slow decay of various radioactive elements including uranium, inside earth
Free energy and reliable, little damage to environment
Aren’t many suitable locations

46
Q

What is wave power?

A

Lots of wave powered turbines around coast. Connected to generator

47
Q

Pros and Cons of Wave Power

A

No pollution

Disturbing sea bed and habitats of marine animals, spoiling view and hazard to boats
Unreliable, waves die when wind drops

Initial costs are high, no fuel costs and minimal running costs, no energy in large scale
Useful

48
Q

What is tidal barrages?

A

Generate electricity
Big fans built across river estuaries, turbines in them.
Tide fills estuary. Allowed in at controlled speed.
Tide produced by gravitational pull of Sun and Moon

49
Q

Pros and Cons of Tidal Barrages

A

No Pollution
Reliable, happen twice a day without fail, alway near predicted height.

Prevent free access by boats, spoiling view and altering habitat.
Height is variable so lower tides make less energy. Don’t work when water level same either side of barrage

Initial cost=high
No fuel costs and minimal running cost

Large amount of energy

50
Q

What are biofuels?

A

Renewable energy resources created from either plant products or animal dung. Can be solid, liquid or gas and burnt to produce electricity or run cars in same way as fossil fuels.

Carbon neutral, debate as only true if keep growing plants at rate you’re burning things

Reliable, crops short time growth, all year round. No immediate response- stored.

51
Q

Biofuel cost

A

Very high so worry that crops grown for bio fuels leaves no water or room for crops for food

Large areas of forest cleared to make room to grow bio fuels, losing habitats. Decay and burning of vegetation increases CO2 and methane emissions

Physics (6 decks)

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