(a) Define Power and state its S1 unit.
(b) A torch bulb is rated 5 V and 500 mA. Calculate:
(i) Power
(ii) Resistances
(iii) Energy consumed when it is lighted for 2½ hours.
Answer:
(a)
Power is the amount of electric energy consumed in a circuit per unit time.
Power, P = VI
Where,
- V is the potential difference.
- I is the electric current.
SI unit of power is Watt (W).
(b)
Given,
- Potential difference, V = 5 V
- Current, I = 500 mA = 500 * 10 ^{ -3 } A = 0.5 A
(i)
We know that,
Power, P = V*I
= 5 * 0.5
= 2.5 W
(ii)
We know that,
Resistance, R = V / I
= 5 / 0.5
= 10 ohm
(iii)
Given,
- Time, t = 2.5 hours
We know that,
Energy consumed = P * t
= 2.5 * 2.5
= 6.25 Wh