Energy

Question 1

What happens when a system changes?

Answer 1

There are changes in the way energy is stored

Question 2

calculation of kinetic energy

Answer 2

kinetic energy (J) = 0.5 x mass (kg) x speed squared (m/s)

Question 3

the calculation for the gravitational potential energy gained by raising an object above ground level

Answer 3

gravitational potential energy (J) = mass (kg) x gravitational field strength (N/kg) x height (m)

Question 4

the amount of elastic energy stored in a stretched or compressed spring can be found with the equation:

Answer 4

Ee (J) = 0.5 x spring constant (N/m) x extension ^2 (m)

Question 5

the equation for power (energy transfer)

Answer 5

energy transferred/ time

Question 6

equation for power (word done)

Answer 6

work done / time

Question 7

what is wasted energy caused by?

Answer 7

unwanted energy transfer

Question 8

How can unwanted transfers be reduced ?

Answer 8

lubrcation- reduces the friction that produces heat

tightening any loose parts - prevents unwanted vibration that wastes energy as sound

thermal insulation - resuces heat loss

Question 9

What is thermal conductivity?

Answer 9

a measure of how well a material conducts energy when it is heated.

Question 10

What does the rate of cooling depend on?

Answer 10

the thickness and thermal conductivity of the walls

Question 11

what is special heat capacity?

Answer 11

the amount of energy required to raise the temperature of one kilogram of the substance by 1 degree celsius

Question 12

what is internal energy?

Answer 12

the total kinetic and potential energy of all the particles that make up a system

Question 13

what is the result of doing work on a system

Answer 13

it increases the energy stored in a system

Question 14

How does heating change the energy in a system

Answer 14

by increasing the energy of the particles within it

Question 15

as energy increases……

what happens to the state and the temperture

Answer 15

it will either increase the temperature or produce a change of state

Question 16

the law of conservation of energy is ……

Answer 16

energy cannot be created or destroyed

Question 17

the higher the thermal conductivity of a material

Answer 17

the higher the rate of energy transfer by conduction across the material.

Question 18

thin walls with hight thermal conductivity will conduct heat …..

Answer 18

the quickest and the building will cool down rapidly

Question 19

what are the three ways in which thermal energy can be transferred?

Answer 19

radiation, convection and conduction

Question 20

when does convection occur?

Answer 20

when particles with a lot of heat energy in a liquid or gas move and take the place of particles with less energy

Question 21

Heat energy is transferred from ______________________ places by convection

Answer 21

hot to cooler

Question 22

How is heat energy transferred from homes?

convection, conduction, radiation

Answer 22

convection - cold air can enter the house through gaps in the doors and windows and convection current can transfer heat energy in the loft to the roof tiles

conduction - through the walls, floor, roof and windows.

radiation - through the walls, roof and windows.

Question 23

materials with low thermal conductivity are _______ insulators

Answer 23

good

Question 24

what are the several ways in which you can reduce heat loss in homes

Answer 24

• carpets, curtains and draught excluders
• double glazing
• cavity wall insulation
• loft insulation

Question 25

how does double glazing reduce heat loss through windows?

Answer 25

double glazing has a vacuum in between the two panes of glass which means that there will be no conduction or convection

if double glazing has air, convection is minimised because there is little room for the air to move. Air is a poor conductor so there will be very little heat loss by conduction

Question 26

how is heat loss reduced through cavity wall insulation and loft insulation?

Answer 26

the insulating material is blown into the gap between the brick and the inside wall.

Insulating materials have low thermal conductivity and so this reduces the heat loss by conduction. The material also prevents air circulating inside the cavity, therefore reducing heat loss by convection.