A series circuit consists of three identical lamps connected to a battery as shown in Fig. `7.13`.
when the switch `S` is closed, what happens
(a) to the intensities of lamps `A and B`,
(b) to the intensity of lamp `C`,
( c ) to the current in the circuit , and
(d) to the voltage drop across the three lamps ?
Does the power dissipated in the circuit increase, decrease, or remain the same ?

Options

A. (i) , (ii)
B. (i),(ii),(iii)
C. (ii) ,(iii) ,(iv)
D. all

Answer

D

Explanation

Resistances of each bulb = `R`
Before closing the switch

`I = V/(3R), P_(A) = P_(B) = P_(C) = ((V//3)^(2))/(R ) = (V^2)/(9R)`
Total power ` P = (V^2)/(3R)`
After closing the switch :

`i' = (V)/(2R) , P_(A)^(')=P_(B)^(') = ((V//2)^(2))/(R ) = (V^2)/(4R), P_(C)^(') = 0`
Total power `P'=(V^2)/(2R)`
`(P_A^')/(P_A) = (P_B^')/(P_B) = 9/4 = 2.25 P_(C)^(') = 0, (i')/(i) = 3/2 = 1.5`
`(P')/(P) = 3/2 = 1.5`.