Look carefully at the circuits in Figures 3.1 (a) and 3.2. What do you predict a

Question

Look carefully at the circuits in Figures 3.1 (a) and 3.2. What do you predict about the brightness of bulb D in Figure 3.2 compared to bulb A in Figure 3.1 (a)?

Select ALL that apply/are correct.

A) Bulb D will be dimmer than bulb A because current through D will be smaller

B) Bulb D will be brighter than bulb A because current through D will be larger

C) Bulb D will be brighter than bulb A because voltage drop across D will be larger

D) Bulb D will be as bright as bulb A because both current through D and voltage across D are the same as A

E) Bulb D will be brighter than bulb A because voltage drop across D will be smaller

(a) (b) (c) Figure 3.1: Series circuits with (a) one battery and one bulb, (b) one battery and two bulbs and (c) two batteries and two bulbs. (All batteries and all bulbs are assumed to be identical.)

Explanation / Answer

Let us assume the resistance of each bulb be R. (as all bulbs are same)
We know,
I = V/R
As we can see in fig 3.2 , we have two batteries and one bulb , so current supplied to the bulb is more compared to bulb A.
I = 2*V/R

As current is large, Voltage drop across bulb will also be large !!
Therefore,  Correct option :-
B) Bulb D will be brighter than bulb A because current through D will be larger
C) Bulb D will be brighter than bulb A because voltage drop across D will be larger

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