A bulb of 210 W will produce heat in calorie within 5 minutes ?
[Take 4.2 J = 1 cal.]

Question

Accepted Answer

To determine the amount of heat produced by a 210 W bulb in calories over a period of 5 minutes, we need to follow these steps:

1. **Calculate the total energy in joules:**
   - Power (P) is given as 210 watts. Power is the rate of energy consumption, which means the bulb consumes 210 joules per second.
   - Time (t) is given as 5 minutes. To convert this into seconds, multiply by 60 (since 1 minute = 60 seconds):  
     $$
     t = 5 \times 60 = 300 \text{ seconds}
     $$
   - The total energy consumed in joules (E) is calculated by multiplying power by time:  
     $$
     E = P \times t = 210 \times 300 = 63,000 \text{ joules}
     $$

2. **Convert joules to calories:**
   - We know that 4.2 joules is equivalent to 1 calorie. Therefore, to convert joules to calories, divide the total energy in joules by 4.2:  
     $$
     \text{Calories} = \frac{63,000}{4.2} = 15,000 \text{ calories}
     $$

Thus, the bulb produces 15,000 calories of heat in 5 minutes, which corresponds to Option 3.

**Explanation for why other options are incorrect:**

- **Option 1 (63,000 cal):** This option incorrectly assumes that the energy in joules is directly equal to calories without conversion. Since 1 calorie is equivalent to 4.2 joules, the energy in calories must be less than the energy in joules.

- **Option 2 (80,000 cal):** This option exceeds the total energy calculated in joules (63,000 joules) and does not account for the conversion factor from joules to calories.

- **Option 4 (10,500 cal):** This option underestimates the energy conversion from joules to calories. The correct conversion factor results in 15,000 calories, not 10,500.

Therefore, based on the calculations and conversion from joules to calories, Option 3 is the correct answer.