6) Energy

Question 1

How can energy be stored?

Answer 1

• chemical energy
• kinetic energy
• gravitational energy
• elastic energy
• thermal energy
• magnetic energy
• electrostatic energy
• nuclear energy

Question 2

How can energy be transferred?

Answer 2

• mechanically
• electrically
• by heating
• radiation
• light and sound

Question 3

Energy cannot be _______ or _________

Answer 3

• created

- destroyed

Question 4

How would you calculate efficiency?

Answer 4

(useful energy transferred/total energy transferred) × 100 = efficiency

Question 5

What is efficiency calculated in (units)

Answer 5

%

Question 6

How would you draw a Sankey diagram?

Answer 6

• the thickness of the arrows shows how much energy is involved
• useful energy transfers are shown going left to right
• wasteful energy transfers are shown going downwards

Question 7

What are the units for energy?

Answer 7

Joules

Question 8

How can useful energy be calculated?

Answer 8

useful energy = mg∆h
m = mass (kg)
g = gravity (N)
∆h = change in height (m)

Question 9

How is thermal energy transferred along a metal block?

Answer 9

• particles vibrate and pass on this energy to the surrounding particles

Question 10

What is a convection current?

Answer 10

• gas molecules absorb heat energy from heater, the gas expands becoming less dense
• the warmer gas is less dense than the surrounding air so it rises to the ceiling
• as the gas loses heat to its surroundings it becomes more dense
• the cooler, denser gas sinks towards the ground

Question 11

Describe the convection current in a refrigerator:

Answer 11

• air at the top of the fridge transfers some of its thermal energy to the ice box and cools down
• the cooler air is more dense than the surrounding air so it descends down through the shelves on the fridge
• the cold air absorbs thermal energy from food products in the fridge and becomes warmer
• the warmer air is less dense than the surrounding air and it rises up through the fridge towards the ice box

Question 12

What can you say about conduction in metals and gases?

Answer 12

metals - good conductors

gases - insulators or poor conductors

Question 13

How is energy conducted through a non-metallic solid?

Answer 13

• non-metallic solids conduct electricity through the vibrations of the particles to neighbouring particles

Question 14

Why are metals very good conductors?

Answer 14

• particles are close together

- delocalised electrons in lattice

Question 15

Name some ways of reducing the heat loss from a house

Answer 15

• carpets
• double glazing
• wall insulation
• loft insulation

Question 16

Why does warmer water rise upwards in a convection current?

Answer 16

• water heated - expands - lower density than surrounding water therefore rises

Question 17

Which emits more radiation: a hot object or a cold object?

Answer 17

• hot object

Question 18

Which emits more radiation: a dull black object or a shiny bright object?

Answer 18

• a dull black object

Question 19

Which absorbs more radiation: a dull black object or a shiny bright object?

Answer 19

• dull black object

Question 20

Why are shiny bright objects bad radiation absorbers and emitters?

Answer 20

• the shiny surface reflects the radiation

Question 21

How does a vacuum or ‘thermos’ flask keep hot drinks hot (or keep ice-cream cold)?

Answer 21

• it does this by stopping or reducing the transfer of heat by conduction, convection and radiation.

Question 22

What design features reduce conduction in a vacuum flask?

Answer 22

• plastic stopper
• vacuum (poor conductor)
• glass
• plastic case

Question 23

What design features reduce convection in a vacuum flask?

Answer 23

• the stopper

- the vacuum

Question 24

What design features reduce radiation in a vacuum flask?

Answer 24

• silvering

Question 25

How would you calculate work done?

Answer 25

W = F × d
W = work done (joules)
F = force (N)
d = distance moved (m)

Question 26

How would you calculate power?

Answer 26

P = W/t
P = power (J/s) (Watts)
W = work done (J)
t = time taken (s)

Question 27

How would you calculate GPE?

Answer 27

GPE = m × g × h
GPE = gravitational potential energy (J)
m = mass (kg)
g = gravitational field strength (N/kg)
h = height (m)

Question 28

How would you calculate kinetic energy?

Answer 28

KE = 1/2mv²
KE = kinetic energy (J)
m = mass (kg)
v² = speed² (m/s)