To determine the correct fuse rating for an electric device with a power rating of 1 kW (1000 W) when connected to a mains supply of 250 V, we need to follow a systematic approach. ### Step 1: Calculate the Current Drawn by the Device The first step is to calculate the current (I) that the device will draw when it is operating. We can use the formula that relates power (P), voltage (V), and current (I): \[ P = V \times I \] Where: - \( P \) is the power in watts (W), - \( V \) is the voltage in volts (V), - \( I \) is the current in amperes (A). Rearranging the formula to solve for current gives us: \[ I = \frac{P}{V} \] ### Step 2: Substitute the Values Now, we can substitute the values for power and voltage into the formula: \[ I = \frac{1000 \, \text{W}}{250 \, \text{V}} = 4 \, \text{A} \] ### Step 3: Determine the Fuse Rating The calculated current is 4 A. The fuse rating should be slightly higher than the normal operating current to prevent it from blowing during normal operation, but low enough to protect the circuit from excessive current that could cause overheating or fire. ### Step 4: Choosing the Correct Fuse Rating In this case, the closest standard fuse ratings available are: - 2 A - 3 A - 4 A - 5 A Since the device draws 4 A, a 5 A fuse would be appropriate. It allows for normal operation without blowing while still providing protection against excessive current. ### Conclusion: Correct Option Thus, the correct option is **D. 5 A**. ### Explanation of Other Options - **A. 2 A**: This fuse rating is too low for a device that draws 4 A. It would blow immediately upon turning on the device, as it cannot handle the current required for operation. - **B. 3 A**: Similar to the 2 A option, a 3 A fuse is also insufficient for a device that draws 4 A. It would likely blow during normal operation, making it an unsuitable choice. - **C. 4 A**: While this option matches the calculated current, it is not a standard fuse rating. Fuses are typically rated at 2 A, 3 A, 5 A, 10 A, etc. Using a non-standard rating could lead to confusion and is not advisable. ### Summary - The power of the device is 1 kW, and the mains voltage is 250 V. - The current drawn by the device is calculated to be 4 A. - The appropriate fuse rating should be slightly higher than the operating current to prevent nuisance blowing. - The correct fuse rating for this device is 5 A, making option D the right choice. ### Revision Summary - Use the formula \( P = V \times I \) to calculate current. - Ensure the fuse rating is higher than the calculated current but within standard ratings. - A fuse rating that is too low will blow during normal operation. - Always choose the nearest standard fuse rating above the calculated current.