Energy

Question 1

what is a system?

Answer 1

single/group of objects

Question 2

what are closed systems?

Answer 2

• matter/energy can’t leave
• net change in total energy = 0

Question 3

explain the energy transfer of boiling water (system) in a kettle

Answer 3

• energy is transferred to water from heating element
• by heating
• then into water’s thermal energy store
• temp rise

Question 4

explain the energy transfer of boiling water in a kettle (two-object system)

Answer 4

• energy transferred electrically
• to heating element’s thermal energy store
• transfers energy by heating water’s thermal energy store

Question 5

the initial force exerted by a person to throw a ball upwards does work

Answer 5

• energy transfer from chemical energy store of arm
• kinetic energy store of ball and arm

Question 6

a ball dropped from a height is acceleratedby gravity. the gravitational force does work.

Answer 6

• energy transferred from ball’s gpe store
• to kinetic energy store

Question 7

the friction between a car’s brakes and its wheels does work as it slows down.

Answer 7

• energy transfer from wheels’ kinetic energy stores
• to thermal energy store of surroundings

Question 8

in a collision between a car and a stationary object, the normal contact force between the car and the object does work.

Answer 8

• energy transferred from car’s kinetic energy store to other stores
• e.g. elasic potential and thermal energy stores of object and car body
• some transferred away by sound waves

Question 9

for a falling object where there’s no air resistance

Answer 9

energy lost from gpe store = energy gained in the kinetic energy store

Question 10

equation for kinetic energy

Answer 10

E_k= 1/2 m v²

Question 11

what is velocity measured in?

Answer 11

m/s

Question 12

equation for gpe

Answer 12

E_p= m g h

(mass x gravitational field strength x height)

Question 13

what is gravitational field strength measured in?

Answer 13

N/kg

Question 14

equation for elastic potential energy

Answer 14

E_e= 1/2 k e²

(1/2 x spring constant x extension²)

Question 15

what is the spring constant measured in?

Answer 15

N/m

Question 16

what is the extension measured in?

Answer 16

meters

Question 17

what is specific heat capacity?

Answer 17

amount if energy needed to raise temp of 1kg of substance by 1ºC

Question 18

equation linking energy transferred to specific heat capacity

Answer 18

△E= m c △Ø

(change in thermal energy energy = mass x specific heat capacity x temp change)

Question 19

what is specific heat capacity measured in?

Answer 19

J/kgºC

Question 20

how can you set up an investigation on the specific heat capacity of a solid material with two holes?

Answer 20

1. measure mass then wrap in insulator
2. insert thermometer and heater
3. measure initial temp and set pd of power supply to 10V
4. turn on power supply and stopwatch

Question 21

how can you commence an investigation of the specific heat capacity of a solid material with two holes in it?

Answer 21

1. turn on power: energy transferred electrically from power supply to heater’s thermal energy store to material by heating
2. as temp rises, measure it and current every minute for 10 mins
3. turn off power supply
4. use P=IV and then E=Pt

Question 22

why do we insulate the solid block with a thick layer of newspaper when investigating the specific heat capacity of it?

Answer 22

reduce energy transferred to surroundings

Question 23

how do you find the gradient of a graph of energy transferred when trying to find the specific heat capacity?

Answer 23

• △Ø / △E
• 1 divided by (gradient x mass of block)

Question 24

what is dissapated energy?

Answer 24

wasted energy

Question 25

what is the useful and sissipated energy of a mobile phone (system)?

Answer 25

- useful energy transferred to chemical store of battery - energy dissipated when transferred to thermal energy store

Question 26

a cold spoon dropped into an insulated flask of hot soup which is then sealed (closed system)

Answer 26

- energy transferred from soup's thermal energy store - spoon's useless thermal energy store - soup cools slightly - energy transferred within system = no energy left - net change in energy = 0

Question 27

what is conduction?

Answer 27

vibrating particels transfers energy to neighbouring particles

Question 28

what is convection?

Answer 28

- energetic particles move away from hotter to cooler regions - only in liquids and gases

Question 29

what happens when you heat a region of a gas or liquid?

Answer 29

- partciles move faster - space between particles increase - density decreases - flow: warmer, less dense region rises above cooler, more dense

Question 30

how does convection currents occur?

Answer 30

-constant heat source

Question 31

heating a room with a radiator relies on creating convection currents in the iar of the room

Answer 31

- energy transferred from radiator to nearby air particles by conduction - air becomes warmer, less dense as particles move more quicker - warm air rises, replaced by cool air heated again - previously heated air transfers energy to surroundings - cools, becomes denser and sinks - cycle repeats

Question 32

how does air resistance cause energy to be dissipated?

Answer 32

- transfer energy to falling object's kinetic energy store - to thermal energy store

Question 33

how can you investigate the effectiveness of materials as thermal insulators?

Answer 33

- boil water and pour into sealable container to safe level - measure mass - use thermometer measure initial temp - seal and leave for 5 mins using stopwatch - remove lid and measure final temp pour water away and cool container to room temp -repeat using different materials as insulators

Question 34

what can you conclude from an investigation of the effectiveness of materials as thermal insulators?

Answer 34

-lower temp difference = better that material as thermal insulator

Question 35

three main fossil fuels

Answer 35

- coal - oil - gas

Question 36

expand on the non-renewable energy resources

Answer 36

- all run out one day - all damage environment - provide most of our energy

Question 37

expand on the renewable energy resources

Answer 37

- renewed won't run out - less damage to environment - don't provide as much energy - unreliable: depends on weather

Question 38

7 renewable energy resources

Answer 38

1. solar 2. wind 3. waterwaves 4. hydro-electricity 5. bio-fuel 6. tides 7. geothermal