Reason for fuse wire repeatedly getting burnt when used with a good heater:

When a fuse wire is used with a good heater, the current passing through the wire increases beyond its maximum capacity. This causes the wire to heat up and melt, thereby breaking the circuit and preventing any further damage to the heater. However, if the fuse wire has a smaller radius, it will have a lower maximum capacity and will melt quickly. Thus, it will not be able to handle the excess current and will repeatedly get burnt.

Solution:

To prevent the fuse wire from repeatedly getting burnt, it is advised to use a fuse wire with a larger radius. This will increase its maximum capacity, allowing it to handle the excess current without melting quickly. Therefore, the correct option is 'D' - more radius.

Advantages of using a fuse wire with more radius:

1. Higher maximum capacity: A fuse wire with a larger radius has a higher maximum capacity, which means it can handle more current before melting.

2. Longer lifespan: A fuse wire with a larger radius will not melt quickly, which means it will have a longer lifespan and will not need to be replaced as frequently.

3. Better protection: A fuse wire with a larger radius will provide better protection to the electrical appliance as it will be able to handle excess current without getting burnt.

Conclusion:

Using a fuse wire with a larger radius is important to prevent it from repeatedly getting burnt when used with a good heater. This will provide better protection to the electrical appliance and ensure its longevity.