P2

Question 1

If a material has a greater thermal conductivity what does that mean for the energy of the material ?

Answer 1

It means it will have a higher energy per second

Question 2

If you need a good insulator does the thermal conductivity need to be low or high

Answer 2

Low

Question 3

What does the energy transfer per second through a layer of a material depends on ?

Answer 3

The thickness of the material
The thermal conductivity of the material
The temperature difference across the material

Question 4

What is the formula for energy transferred ?

Answer 4

Energy transferred (joules) = mass (kilograms) x specific heat capacity (joules per kilogram per degree celsius) x temprature change( degree )

Question 5

What is the formula for specific heat capacity .

Answer 5

Eneegy transferred(joules) / mass (kilograms) x temprature change (degrees)

Question 6

How much eneegy is required to raise the temprature ?

Answer 6

4200 joules to raise 1kg of water

Question 7

Name three design features to reduce the rate of energy transfer at a home

Answer 7

Any of : 
Loft insulation 
Thicker brick walls 
Double glazed windows 
Aluminium foil (between radiator)
Cavity wall ( air gaps between the brick walls)

Question 8

Describe the energy transfers that occur for a kettle ?

Answer 8

A kettle transferes electrically from the mains ac supply to the thermal energy store of the heating element inside the kettle

Question 9

What is the power rating of an appliance ?

Answer 9

The power of an appliance is the energy that it transferes per second. So the more energy it transfers in a given time the higher its power

Question 10

What is the national grid ?

Answer 10

It is a giant system of cables and transformers that cover the uk and connects power stations to consumers

Question 11

Why is electricity transfered by the national grid at a high pd but low current ?

Answer 11

To transmit a huge amount of power needed. The problem with a high current is you lose loads of energy as the wires overheat and energy is transfered to thermal energy. So its much cheaper to boost the pd really high and keep the current really low.

Question 12

What is the functions of step up step down transformer ?

Answer 12

The step up is used to increased potential difference. ( they have more turns on the secondary coil than the primary coil. As the pd increased by the trnasformer the current deacreased)

The step down transformer is then used to reduce the pd. the current is then increased by the transformer they have more turns of the primary coil than the secondary