7.10 Power of electrical applicances

Question 1

What is power?

Answer 1

The energy transferred per second

Question 2

Write the equation for power, relating energy and time

Answer 2

P = E / t

P = power (Watts)
E = energy transferred (joules)
t = time (Seconds)

Question 3

What is a power rating?

Answer 3

The maximum safe power at which an appliance can operate.

The lower the power rating, the less electricity an appliance uses in a given time, so it’s cheaper to run

(Note an appliance can use more power but may be less efficient, so uses less useful energy

Question 4

Write the equation for power, relating p.d. and current

Answer 4

P = I x V

Power (watts) = current (I) x V (p.d.)

Question 5

Write the equation for power, relating current and resistance

Answer 5

P = I-squared x R

P = power (watts)
I = current (I)
R = resistance (ohms)