The correct answer is: B. more than 15 A.
In a step-down transformer, the output voltage is less than the input voltage, and the output current is greater than the input current. This is because the transformer transfers energy from one circuit to another, and the power in the output circuit must be equal to the power in the input circuit. The power is equal to the product of the voltage and the current, so if the voltage is decreased, the current must increase in order to maintain the same power.
In the case of a 15 A change in the load current, the supply current will change by more than 15 A. This is because the transformer will have to supply more power to the load when the load current increases. The amount of additional power that the transformer must supply is equal to the product of the change in the load current and the output voltage. Therefore, the supply current will increase by more than 15 A.
Here is a more detailed explanation of each option:
- Option A: less than 15 A. This is not possible because the transformer must supply more power to the load when the load current increases. The amount of additional power that the transformer must supply is equal to the product of the change in the load current and the output voltage. Therefore, the supply current will increase by more than 15 A.
- Option B: more than 15 A. This is the correct answer. The transformer must supply more power to the load when the load current increases. The amount of additional power that the transformer must supply is equal to the product of the change in the load current and the output voltage. Therefore, the supply current will increase by more than 15 A.
- Option C: 15 A. This is not possible because the transformer must supply more power to the load when the load current increases. The amount of additional power that the transformer must supply is equal to the product of the change in the load current and the output voltage. Therefore, the supply current will increase by more than 15 A.
- Option D: none of the above. This is not possible because the transformer must supply more power to the load when the load current increases. The amount of additional power that the transformer must supply is equal to the product of the change in the load current and the output voltage. Therefore, the supply current will increase by more than 15 A.