Check sibling questions

(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

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CA Maninder Singh

CA Maninder Singh is a Chartered Accountant for the past 12 years and a teacher from the past 16 years. He teaches Science, Economics, Accounting and English at Teachoo