Three 100 W bulbs are connected in series to a 220 V power source . If 2 of the bulbs are replaced by 60 W bulbs then the brightness of the remaining 100 W bulb will increase or decrease and why?

Asked by Saptarshi Sen | 23rd Nov, 2014, 11:40: AM

Expert Answer:

begin mathsize 14px style When space three space 100 space straight W space bullbs space are space connected space in space series space to space straight a space 220 space straight V space power space source space same space current space will space flow space through space three space bulb According space to space formulaP equals VI comma space Power space is space directly space prortional space to space Voltage. space Hence space same space powers space dissipated space by space three space bulb space and space all space three space bulb space will space have space same space brightness. When space first space two space bulb space is space replaced space by space 60 space straight W space bulb space in space series space with space 100 space straight W space then comma space here space according space to space formula space straight P subscript 1 over straight V subscript 1 equals straight P subscript 2 over straight V subscript 2 equals straight P subscript 3 over straight V subscript 3 straight P subscript 1 equals straight P subscript 2 rightwards double arrow straight V subscript 1 equals straight V subscript 2 equals 60 space straight V But space straight V subscript 3 equals 100 space straight V space Maximum space voltage space dissipated space in space bulb space of space 100 space straight W space hence comma space 100 space Watt space bulb space brightness space will space increases. end style

Answered by Priyanka Kumbhar | 24th Nov, 2014, 03:51: PM