Ham Amateur Radio Technician Practice Exam

Why is the primary winding wire of a voltage step-up transformer typically larger than that of the secondary winding?

1. To reduce inductance

2. To accommodate higher current

3. To improve efficiency

4. To protect against overheating

The correct answer is: To accommodate higher current

In a voltage step-up transformer, the primary winding is designed to handle the power input from the source, while the secondary winding is configured to provide a higher voltage output. According to the principle of conservation of energy, the power in the primary winding (voltage times current, or V_p*I_p) is equal to the power in the secondary winding (V_s*I_s) minus any losses. Because the transformer is stepping up the voltage from primary to secondary, the secondary winding has a higher voltage but a lower current due to this conservation. Thus, the primary winding wire needs to be larger in diameter to accommodate a potentially higher current compared to the secondary winding. A larger wire size helps to decrease resistance, which minimizes the heating effect of current flowing through the conductor. Proper sizing is vital for safety and performance, as it allows the primary coil to efficiently handle the input current without excessive voltage drop or overheating, ensuring the transformer's reliable operation.