Question

A bulb of 60 volt and 10 watt is connected with 100 volt of ac source with an inductance coil in series. If bulb illuminates with it's full intensity then value of inductance of coil is (ν= 60 Hz)

• A. 1.28 H
• B. 2.15 H
• C. 3.27 H
• D. 3.89 H

Answer 1

Answer: (A)

1.28 H

Answer 2

Resistance of the bulb $R = \frac { 60 \times 60 } { 10 } = 360 \Omega$ .

For maximum illumination, voltage across the bulb

By using $( 100 ) ^ { 2 } = ( 60 ) ^ { 2 } + V _ { L } ^ { 2 }$

⇒ $V _ { L } = 80 \mathrm {~V}$

Current through the inductance (L) = Current through the bulb Also

⇒ $L = \frac { V _ { L } } { ( 2 \pi v ) i } = \frac { 80 } { 2 \times 3.14 \times 60 \times \frac { 1 } { 6 } } = 1.28 \mathrm { H }$.