A motor of power 60 W draws current 5 A from a source of 15 V. What is loss of power ?

Options

A. 30 W
B. 25 W
C. 20 W
D. 15 W

Answer

To solve the problem of calculating the loss of power in the motor, we can follow these steps:

### Step 1: Identify the given values
- Power of the motor (P_motor) = 60 W
- Current drawn by the motor (I) = 5 A
- Voltage from the source (V) = 15 V

### Step 2: Calculate the resistance of the motor
Using Ohm's law, we know that:
\[ V = I \times R \]
We can rearrange this to find the resistance (R):
\[ R = \frac{V}{I} \]
Substituting the given values:
\[ R = \frac{15 \, \text{V}}{5 \, \text{A}} = 3 \, \Omega \]

### Step 3: Calculate the power loss in the motor
The power loss due to resistance in the motor can be calculated using the formula:
\[ P_{loss} = I^2 \times R \]
Substituting the values we have:
\[ P_{loss} = (5 \, \text{A})^2 \times 3 \, \Omega = 25 \times 3 = 75 \, \text{W} \]

### Step 4: Calculate the actual loss of power
To find the loss of power, we subtract the power of the motor from the power loss calculated:
\[ \text{Loss of Power} = P_{loss} - P_{motor} \]
Substituting the values:
\[ \text{Loss of Power} = 75 \, \text{W} - 60 \, \text{W} = 15 \, \text{W} \]

### Conclusion
The loss of power in the motor is **15 W**.

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