Unit 1: Chapter 3 - Electrical Energy

Question 1

Electrical Power

What is power?

How do you calculate power?

How do you calculate efficiency of power?

Answer 1

P = E / t

Power (watts) = Energy / time

The more powerful an appliance, the faster the rate at which it transfers energy.

E.g. How powerful is a weightlifter?

30kg = 300N and lifts it by 1 metre. This would give a GPE of 300J but it is lifted in 0.5s.

The rate of energy transfer would be 600j/s (300j/0.5s) so the total power output would be 600W.

EFFICIENCY AND POWER

Efficiency = useful power out / useful power in

E.g. 20W / 80W x 100% = 25%

Question 2

Using Electrical Energy

Answer 2

E = P x t

Energy transferred in kilowatts (kWh) = Power (kW) x time taken to tranfer energy (h)

Total cost = number of kWh used x cost per kWh

Question 3

Electrical Appliances

What should you consider when choosing an electrical appliance?

What are electrical appliances used to do?

Answer 3

Electrical appliances produce useful and wasted energy at a flick of a switch.

For e.g. Light bulbs produce light energy (useful) but also heat energy (wasted).

When choosing electrical appliances, you want choose the an appliance designed to waste as little energy as possible.

Question 4

Cost Effectiveness

What do we have to consider when comparing cost-effectiveness?
How can we detect heat loss in a house?

Answer 4

When comparing cost-effectiveness, we need to consider:

• Installation prices of equipment
• Running costs of fuel and maintenance.
• Environmental costs such as:
  
  • removal of old equipment
  • tax charges such as carbon taxes
• other costs such as interest or loans

We can use infra-red cameras to detect heat loss.