Energy Transfers (3)

Question 1

What is electric current?

Answer 1

The rate of flow of electric charge

Question 2

What is potential difference?

Answer 2

Work done per coulomb of charge that passes between two points in a circuit

Question 3

The resistance of the metal filament inside the bulb increases as the potential difference across the bulb increases.
Explain why

Answer 3

Metals contain free electrons and ions. As the temperature of the filament increases, the ions vibrate faster so electrons collide more frequently with the ions.

Question 4

Use the data in the table to evaluate the cost - effectiveness of an LED bulb compared to a CFL

Answer 4

Over a period of 50 000 hours CFLs cost £15.50 to buy, LED costs £29.85 to buy so CFLs are cheaper

Question 5

Suggest one benefit of developing brighter and more efficient LED chips

Answer 5

Price of LED bulbs will drop

Question 6

The air inside the fridge forms a convection current when the fridge door is closed.
Explain why

Answer 6

Air near freezer compartment is cooled. The cool air is more dense so cooler air falls. Air at bottom is displaced.

Question 7

A householder concludes that the energy used in one year is directly proportional to the volume of the fridge.
Explain why her conclusion is not correct

Answer 7

If the volume is doubled, energy use is not doubled. Volume : energy is not a constant ratio