Two bulbs when connected in parallel to a source take 60 W each, the power consumed, when they are connected in series with the same source is

Options

A. 15 W
B. 30 W
C. 60 W
D. 120 W

Answer

To solve the problem, we need to find the power consumed by two bulbs when they are connected in series after knowing their power consumption when connected in parallel.

### Step-by-Step Solution:

1. **Identify the Power Consumption in Parallel:**
Each bulb consumes 60 W when connected in parallel. Therefore, we have:
\[ P_1 = 60 \, \text{W} \quad \text{and} \quad P_2 = 60 \, \text{W} \]

2. **Calculate the Equivalent Resistance of Each Bulb:**
The power consumed by a resistor (bulb) can be expressed using the formula:
\[ P = \frac{V^2}{R} \]
Rearranging this gives us:
\[ R = \frac{V^2}{P} \]
Since both bulbs have the same power rating, we can denote their resistances as \( R_1 \) and \( R_2 \):
\[ R_1 = R_2 = \frac{V^2}{60} \]

3. **Calculate the Total Resistance in Series:**
When connected in series, the total resistance \( R_{total} \) is the sum of the individual resistances:
\[ R_{total} = R_1 + R_2 = \frac{V^2}{60} + \frac{V^2}{60} = \frac{2V^2}{60} = \frac{V^2}{30} \]

4. **Calculate the Power in Series:**
The power consumed in series can be calculated using the formula:
\[ P_{total} = \frac{V^2}{R_{total}} \]
Substituting the expression for \( R_{total} \):
\[ P_{total} = \frac{V^2}{\frac{V^2}{30}} = 30 \, \text{W} \]

5. **Conclusion:**
Therefore, the power consumed when the two bulbs are connected in series is:
\[ P_{total} = 30 \, \text{W} \]

### Final Answer:
The power consumed when the bulbs are connected in series is **30 W**.