Question

A 300 V, 5 A, LPF wattmeter has a full scale of 300 W. The wattmeter can be used for loads supplied by 300 V ac mains with a maximum power factor of \(\underline{\hspace{2cm}}\) (rounded off to one decimal place).

Hint:

For calculating the power factor, use the formula \( P = VI\cos(\phi) \) and solve for \( \cos(\phi) \).

Answer 1

Correct Answer: 0.2

To calculate the maximum power factor, we use the following formula for the power factor:
\[ P_{\text{max}} = V_{\text{max}} I_{\text{max}} \cos(\phi) \] Given that \( P_{\text{max}} = 300 \, \text{W} \), \( V_{\text{max}} = 300 \, \text{V} \), and \( I_{\text{max}} = 5 \, \text{A} \), we can solve for the power factor \( \cos(\phi) \) as follows: \[ 300 = 300 \times 5 \times \cos(\phi) \] \[ \cos(\phi) = \frac{300}{1500} = 0.2. \] Thus, the maximum power factor is \( 0.2 \).