Topic 1 - Energy (2)

Question 1

SPECIFIC HEAT CAPACITY:
Explain why different materials have different heat capacities?

Answer 1

more energy needs to be transferred to the thermal energy store of some materials to increase their temperatures than others

Question 2

SPECIFIC HEAT CAPACITY:
How much energy is needed to warm 1kg of water by 1degree C?

Answer 2

4200 joules

Question 3

SPECIFIC HEAT CAPACITY:
How much energy is neeeded to warm 1kg of mercury by 1 degree C?

Answer 3

139 joules

Question 4

SPECIFIC HEAT CAPACITY:
What do materials that ‘store’ a lot of energy do when they warm up and cool down?

Answer 4

• they need to gain lots of energy in their thermal energy stores to warm up
• but they will also transfer lots of energy when they cool down again

Question 5

SPECIFIC HEAT CAPACITY:
What is specific heat capacity?

Answer 5

The amount of energy needed to raise the temperature of 1kg of a substance by 1 degree C

Question 6

SPECIFIC HEAT CAPACITY:
Required practical: Investigating specific heat capacities:
Why does turning on the power cause the temperature of the block to increase?

Answer 6

• when you turn on the power, the current in the circuit does work on the heater
• this transfers energy electrically from the power supply to the heater’s thermal energy store
• this energy is then transferred to the material’s thermal energy store by heating, causing the material’s temperature to increase

Question 7

SPECIFIC HEAT CAPACITY:
Required practical: Investigating specific heat capacities:
Why would you cover the block in an insulating layer?

Answer 7

to reduce energy transferred from the block to the surroundings

Question 8

SPECIFIC HEAT CAPACITY:
Required practical: Investigating specific heat capacities:
When calculating specific heat capacity (from the energy transferred (to the thermal energy store of the block) and temperature) what do you assume?

Answer 8

all the energy supplied to the heater has been transferred to the block

Question 9

SPECIFIC HEAT CAPACITY:
Required practical: Investigating specific heat capacities:
How would you alter the experiment to work out the specific heat capacity of a liquid?

Answer 9

place the heater and therometer in an insulated beaker filled with a known mass of the liquid

Question 10

CONSERVATION OF ENERGY AND POWER:
What is the conservation of energy principle?

Answer 10

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

Question 11

CONSERVATION OF ENERGY AND POWER:
When energy is transferred between stores, what happens to the energy that is not transferred usefully into the store you want it to?

Answer 11

some energy is always DISSIPATED when an energy transfer takes place

Question 12

CONSERVATION OF ENERGY AND POWER:
Why is dissipated enregy sometimes called ‘wasted energy’?

Answer 12

the energy is stored in a way that is not useful (usually energy is transferred to thermal energy stores)

Question 13

CONSERVATION OF ENERGY AND POWER:
A mobile phone is a system. How is energy transferred between stores when using a phone?

Answer 13

• energy is usefully transferred from the chemical energy store of the battery in the phone
• but some of this energy is dissipated in this transfer to the thermal energy store of the phone

Question 14

CONSERVATION OF ENERGY AND POWER:
Energy transfers for closed systems: Describe the energy transfers when a cold spoon is dropped onto an insulated flask of hot soup which is then sealed? Describe the energy transfers.
include the net change in energy

Answer 14

• assume that the flask is a perfect thermal insulator so the soup and the spoon form a closed system
• energy is transferred from the thermal energy store of the soup to the useless thermal energy store of the spoon (causing the soup to cool down slightly)
• Energy transfers have occured within the system, but no energy has left the system - so the net change in energy is 0

Question 15

CONSERVATION OF ENERGY AND POWER:
What is the net change in energy for a closed system?

Answer 15

the net change in energy is 0
(energy transfers occur within the system but no energy has left the system)

Question 16

CONSERVATION OF ENERGY AND POWER:
What is power?

Answer 16

Power is the rate of energy transfer/ the rate of doing work

Question 17

CONSERVATION OF ENERGY AND POWER:
What units is power measured in?

Answer 17

watts,w

Question 18

CONSERVATION OF ENERGY AND POWER:
How much energy is transferred per 1 watt of power?

Answer 18

One watt = 1 joule of energy transferred per second

Question 19

CONSERVATION OF ENERGY AND POWER:
Two identical cars but with different power engines race along a straight track - what will happen?

Answer 19

• the car with the more powerful engine will reach the finish line faster than the other car
• it will transfer the same amount of energy but over less time

Question 20

CONSERVATION OF ENERGY AND POWER:
Why is a powerful machine not just one that can exert a strong force?

Answer 20

a powerful machine transfers lots of energy in a SHORT SPACE OF TIME

Question 21

CONDUCTION AND CONVECTION:
Define conduction?

Answer 21

the process where vibrating particles transfer enrgy to neghbouring particles

Question 22

CONDUCTION AND CONVECTION:
What state of matter does conduction usually occur in? Why?

Answer 22

• conduction mainly occurs in solids
• particles in liquids and gases are much more free to move around so they will usually transfer energy by convection

Question 23

CONDUCTION AND CONVECTION:
How is energy transferred to an object when it is being heated? (conduction)

Answer 23

• energy is transferred to the thermal store of the object
• this energy is shared across the kinetic energy stores of the particles in the object

Question 24

CONDUCTION AND CONVECTION:
How do vibrating particles cause conduction?

Answer 24

• particles in the part of the object that is being heated vibrate more and collide with each other
• these collisions cause energy to be transferred between particles’ kinetic energy stores
• this is conduction
• this process continues throughout the object until the energy has been transferred to the other side of the object

Question 25

CONDUCTION AND CONVECTION: What will happen when energy has been transferred to the other side of a solid object? (conduction)

Answer 25

- usually transferred to the thermal energy store of the surroundings (or anything else touching the object)

Question 26

CONDUCTION AND CONVECTION: What is thermal conductivity?

Answer 26

a measure of how quickly energy is transferred through a material by conduction. - materials with a high thermal conductivity transfer energy between their particles quickly by conduction

Question 26

CONDUCTION AND CONVECTION: What states of matter can convection occur in?

Answer 26

- liquids - gases

Question 27

CONDUCTION AND CONVECTION: Define convection?

Answer 27

- the process where high energy particles move away from hotter to cooler regions

Question 28

CONDUCTION AND CONVECTION: How is energy transferred when a liquid or gas is heated?

Answer 28

- energy is transferred by heating to the thermal energy store of the liquid or gas - like in conduction, this energy is shared across the kinetic energy stored of the gas or liquid's particles

Question 29

CONDUCTION AND CONVECTION: Explain how a convection current can be created?

Answer 29

- particles in liquids and gases are able to move (unlike in solids) - heating a region of a liquid or gas causes the particles to move faster and the space between the induvidual particles to increase - the density of the region being heated then decreases - liquids and gases can flow, so the warmer less dense region will rise amove denser - If there is a constant heat source a convection current will be created

Question 30

CONDUCTION AND CONVECTION: What does there need to be for a convection current to be created?

Answer 30

a constant heat source