Q4

 

Lamps in Series

Comparison of light outputs in following two cases.

A. One lamp rated 250 Volt 100 Watts is connected across 250 Volts supply.

B. Two lamps rated 250 Volts 100 Watts are placed side by side and connected in series across 250 Volts supply.

How is light output in case B as compared to in case A.

1.       More than double

2.      Double

3.      Less than double

4.      Equals

5.      More than half

6.      Half     

7.      Less than half

                          and How?

 

Answer

Readers,
Quiz is a mental exercise to enhance reasoning power in the subject. Hence personal attempt for reply is expected before jumping to answer. Answer given here is just for confirmation.

Proceed

   Case B has two lamps across rated voltage but connected in series. In series connection resistance of both lamps gets added up. So circuit resistance will be double. Current I = V/R that R that reduces to one forth. Heat generated is proportional to power consumed. So also heat produced is one fourth. Visible light is emitted only after specific temperature attained by filament. Most of the heat is consumed in raising temperature of the filament. Heat produced to light emitted is not a straight-line relation. Radiant Efficiency is increasing with temperature. Therefore, as obvious light output of each lamp is very less than one forth. There are two lamps are side by side. So total light output is very less than half.