An immersion rod heats a bucket of water in 15 minutes, To make the water boil in 10 minutes, the:

Options

A. length of heating element of the rod should be increased
B. length of heating element of the rod should be reduced
C. supply voltage should be reduced
D. heating element of larger diameter should be used

Answer

To solve the problem of how to make the water boil in 10 minutes instead of 15 minutes using an immersion rod, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Heat Production Formula**:
The heat produced (H) by the immersion rod can be expressed using the formula:
\[ H = \frac{V^2 \cdot T}{R} \]
where \( R \) (the resistance) is given by:
\[ R = \frac{\rho \cdot L}{A} \]
Here, \( \rho \) is the resistivity of the material, \( L \) is the length of the heating element, and \( A \) is the cross-sectional area of the heating element.

2. **Relate Heat to Time**:
The heat produced is directly proportional to the time (T) the current flows through the heating element. Thus, if we want to reduce the time from 15 minutes to 10 minutes, we need to increase the heat produced in a shorter time.

3. **Analyze the Relationship**:
From the formula, we can see that:
\[ H \propto \frac{T}{L} \]
This means that for a constant voltage (V), if we want to decrease the time (T) to boil the water, we need to adjust the length (L) of the heating element.

4. **Determine the Required Change**:
Since we want to boil the water in 10 minutes instead of 15 minutes, we need to increase the heat output. To do this, we can either increase the voltage or reduce the length of the heating element. However, reducing the length of the heating element is a more practical solution in this context.

5. **Conclusion**:
Therefore, to make the water boil in 10 minutes, the length of the heating element of the rod should be reduced.

### Final Answer:
The length of the heating element of the rod should be reduced.

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