Energy

Question 1

What are the eight energy stores?

Answer 1

thermal, kinetic, gravitational potential, elastic potential, chemical, magnetic, electrostatic, nuclear

Question 2

How can energy be transferred?

Answer 2

mechanically, electrically, heating, radiation

Question 3

Describe the energy transfers that occur when the wind causes a windmill to spin.

Answer 3

• energy transferred mechanically
• from kinetic energy store of wind
• to kinetic energy store of windmill

Question 4

When is energy transferred away the kinetic energy store?

Answer 4

when an object slows down

Question 5

What does kinetic energy depend on?

Answer 5

mass and speed

Question 6

What is the formula for kinetic energy?

Answer 6

1/2 x mass x velocity squared

Question 7

What is the formula for gravitational potential energy?

Answer 7

mass x gravitational field strength x height

Question 8

What is the formula for elastic potential energy when the limit of proportionality hasn’t been exceeded?

Answer 8

1/2 x spring constant x extension squared

Question 9

What is specific heat capacity?

Answer 9

amount of energy needed to heat 1kg of a substance by 1’C

Question 10

What is the formula which includes specific heat capacity?

Answer 10

change in thermal energy = mass x specific heat capacity x temp. change

Question 11

What is the Conservation of Energy Principal?

Answer 11

energy can be transferred usefully, stored or dissipated, but can never be created or destroyed

Question 12

What is dissipated energy also known as?

Answer 12

wasted energy

Question 13

What is power?

Answer 13

the rate of doing work

Question 14

What is power measured in?

Answer 14

watts

Question 15

From which equations can you calculate power?

Answer 15

power = energy transferred 
               ---------------------------
                           time
power = work done
               ----------------
                     time

Question 16

What is a powerful machine?

Answer 16

one which transfers a lot of energy in a short space of time

Question 17

What is conduction?

Answer 17

vibrating particles transfer energy to neighbouring particles

Question 18

What is thermal conductivity?

Answer 18

a measure of how quickly energy is transferred through a material by conduction

Question 19

What is convection?

Answer 19

the energetic particles move away from hotter to cooler regions

Question 20

How can a convection current be created?

Answer 20

if there is a constant heat source

Question 21

Does warm air rise or sink?

Answer 21

rise

Question 22

How can you reduce heat loss in homes?

Answer 22

• thick walls of a material with low thermal conductivity

- thermal insulation

Question 23

What are the ways of thermally insulating your home?

Answer 23

• cavity walls which are inner and outer wall with air gap in the middle reducing conduction
• loft insulation reducing convection currents in lofts
• double glazed windows reducing conduction
• draught excluders (around doors and windows) reducing convection

Question 24

How can you improve efficiency of objects?

Answer 24

insulation, lubrication, streamlining

Question 25

What is the formula for efficiency?

Answer 25

total power input

Question 26

Explain how a cavity wall insulation reduces the amount of energy transferred out of the house.

Answer 26

• reduces convection
• also reduces conduction
• insulating foam has low thermal conductivity so low rate of energy transfer