When electric bulbs of same power, but different marked voltage are connected in series across the power line, their brightness will be :

Options

A. directly proportional to their marked voltages directly proportional to the squares of their marked voltages
B. inversely proportional to the squares of their marked voltages
C. directly proportional to the squares of their marked voltages
D. inversely proportional to the squares of their marked voltages.

Explanation

To solve the problem of how the brightness of electric bulbs of the same power but different marked voltages behaves when connected in series, we can follow these steps:

### Step 1: Understand the relationship between power, voltage, and resistance
The power \( P \) of an electric bulb can be expressed in terms of its voltage \( V \) and resistance \( R \) using the formula:
\[ P = \frac{V^2}{R} \]
From this, we can derive the resistance of each bulb:
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