Explain why the d.c. from the generator must be changed to a.c. before it is transmitted.

Direct current (DC) from the generator needs to be converted to alternating current (AC) before it is transmitted for several reasons:

1. Efficiency in Power Transmission: AC can be transmitted over long distances with less power loss compared to DC. This is because AC voltage can be easily increased or decreased using a transformer. High voltage is used for long-distance transmission to reduce power loss, and then it is stepped down for safe use in homes and businesses.

2. Cost-Effectiveness: The infrastructure for AC transmission is less expensive to build and maintain than DC. This is because AC systems are simpler and require fewer components.

3. Safety: AC is safer to transmit over long distances because it changes direction 50 or 60 times per second. This means that the risk of electric shock is lower with AC than with DC.

4. Use of Transformers: Most electrical devices and appliances are designed to operate on AC. This is because AC can be easily transformed to different voltages using a transformer, making it more versatile for different uses.

In summary, the conversion of DC from the generator to AC before transmission is primarily for efficiency, cost-effectiveness, safety, and compatibility with most electrical devices.