Question

A 230 V lamp is rated to pass a current of 0.24 A. Calculate its power output. If a second similar lamp is connected in parallel to the lamp, calculate the supply current required to give the same power output in each lamp.
1. 0.24 A
2. 1.5 A
3. 1.9 A
4. 0.48 A

Answer 1

Correct Answer - Option 4 : 0.48 A

Concept:

Power Loss in a resistor is product of Voltage and current

P = V.I …… (1)

From ohm's law

V = I.R

\(I\; = \;\frac{V}{R}\)

Substituting the value of I in (1)

\(P = V.\frac{V}{R} = \frac{{{V^2}}}{R}\)

Calculation:

Method 1:

P = 230 × 0.24 = 55.2 W

R₁ = ( 230 )² / 55.2 = 958.33 Ω 

R₂ = 958.33 Ω 

R_eq =  958.33 / 2 = 479.165 Ω 

I = 230 / 479.165 = 0.48 A

Method 2:

The lamp is rated to pass a current of 0.24 A and another lamp has the same specifications.

Also when connected across the same voltage source, the input current will be doubled.

I = 0.24 × 2 = 0.48 A