Energy

Question 1

what is the law of conservation of energy?

Answer 1

energy is never created or destroyed, only transferred.

Question 2

what is the equation for kinetic energy?

Answer 2

1/2 x mass, m x speed^2, v^2

kinetic energy measured in joules,
mass measured in kg
speed in m/s^2

Question 3

what is the equation for work done?

Answer 3

work done, W = force, F x distance, s

distance measured in metres,
work done in joules,
force in newtons

Question 4

equation for weight

Answer 4

mass x gravitational field strength.

Question 5

change in gravitational potential energy

Answer 5

1. weight x change in height
2. mass, m x gfs, g x change in height

Question 6

equation for elastic potential energy

Answer 6

1/2 x spring constant, k x extension^2, e^2

Question 7

what are the three ways heat can be transferred by?

Answer 7

• convection
• conduction
• radiation

Question 8

how is heat transferred in solids?

Answer 8

by conduction

Question 9

how is heat transferred in fluids?

Answer 9

by convection

Question 10

how is heat transferred in empty space?

Answer 10

by radiation

Question 11

what happens in conduction?

Answer 11

vibrating particles transfer energy to nearby particles

Question 12

how does conduction work?

(3 marker)

Answer 12

• the vibrating particles gain kinetic energy by heating up
• these particles collide more with nearby particles and this repeats
• the heat is then spread out evenly.

Question 13

why does conduction occur mainly in solids?

(2 marker)

Answer 13

• the particles are tightly packed together
• this means there would be more collisions that pass on the energy.

Question 14

define thermal conductivity

Answer 14

how well objects transfer thermal energy by conduction.

Question 15

give one example of an object with high thermal conductivity

Answer 15

metal

Question 16

give one example of an object with low thermal conductivity

Answer 16

plastic

Question 17

how does convection work?

(4 marker)

Answer 17

• the particles gain kinetic energy and begin to collide more frequently and forcefully.
• by the process of random diffusion the particles with energy move away from the warmer side to the cooler side.
• this means that the particles in the warmer region are more spread out than the particles in the cooler side.
• therefore, the fluid on the warmer side expands and becomes less dense than the fluid on the cooler side.

Question 18

how is a convection current formed?

(3 marker)

Answer 18

• when the fluid is heated, the warmer particles spread out and are on top of the cooler particles as they become less dense.
• however they lose the warmth as they are further from the source of heat
• so the cooler particles become heated again and this process repeats
• this forms a convection current.

Question 19

how can we reduce convection?

Answer 19

• stop the free flow of fluids

Question 20

how can radiation be carried if not by particles?

Answer 20

by infrared waves

Question 21

how can we reduce energy loss?

Answer 21

• thermal insulation
• lubrication

Question 22

how would sealing the house shut reduce heat loss?

Answer 22

air wouldnt be able to pass out by convection.

Question 23

how can we seal the the house?

Answer 23

using foam seals

Question 24

how can we reduce heat loss by conduction?

Answer 24

• using cavity walls
• using double glazed windows

Question 25

how do cavity walls reduce heat loss? | (2 marker)

Answer 25

* they have an air gap between two layers of brick walls which traps the air. * air is a poor thermal conductor

Question 26

why is an air gap not efficient in cavity walls?

Answer 26

heat can travel through air by convection

Question 27

how do we fix the air gap?

Answer 27

fill the gap with insulating foam | this reduces heat loss by both convection and conduction

Question 28

how is double glazing efficient? | (3 marker)

Answer 28

* it is essentially 2 panes of windows with an air gap between them * air is a poor thermal conductor * therefore heat loss by conduction is reduced.

Question 29

why is friction not useful?

Answer 29

friction reduces the efficiency of energy transfer

Question 30

how can we reduce friction?

Answer 30

-using oil -making planes and cars more streamlined | streamlined to reduce friction with air resistance, therefore less fuel.

Question 31

how do wind turbines work? | (3 marker)

Answer 31

* as the turbine spins, the generator also turns * the kinetic energy is transferred to electrical energy * this is sent to the national grid.