Question

Two electric bulbs $A$ and $B$ rated $200V\sim 100W$ and $200V\sim 60W$ are connected in series to a $200V$ line. Then the potential drop across.

• A. Each bulb is $200V$
• B. $100W$ bulbs is greater than across $60W$ bulb
• C. $100W$ bulbs is smaller than across $60W$ bulb
• D. Each bulb is $100V$

Answer 1

The correct option is C $100W$ bulbs is smaller than across $60W$ bulb

Given:

The rating of the first bulb is $200V-100W$

The rating of the second bulb is $200V-60W$

The resistance of the first bulb is:

$R_1=\frac{{200}^2}{100}$

$\Rightarrow 400\Omega$

The resistance of the second bulb is:

$R_2=\frac{{200}^2}{60}$

$\Rightarrow \frac{2000}{3}\Omega$

Since the two bulbs are connected in series,

The equivalent resistance of the circuit is:

$R_{eq}=400+\frac{2000}{3}$

$\Rightarrow \frac{3200}{3}$

So the current drawn is $I=\frac{200}{3200/3}=\frac{33}{160}$

Now, the voltage drop is given as $V=IR$

So, the voltage will be higher for the higher values of the resistance. So, the bulb of $100W$ has less potential as compared to bulb of $60W$.