Question 3 - Past Year - 5 Mark Questions - Chapter 12 Class 10 - Electricity

(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