Explanation:
In an SCR (Silicon Controlled Rectifier) circuit, the angle of conduction can be changed by changing the gate voltage. This is because the gate voltage is used to trigger the SCR into conduction.

Working Principle of SCR:
SCR is a four-layered, three-terminal device. It consists of a P-type layer, an N-type layer, and two P-type layers. The two P-type layers in the middle are connected to the anode and cathode terminals. The N-type layer acts as the gate terminal.

The working principle of SCR is based on the fact that the device can be triggered into conduction by applying a voltage pulse to the gate terminal. Once triggered, the SCR will remain in conduction until the anode current falls below a certain threshold level.

Angle of Conduction:
The angle of conduction refers to the portion of the AC voltage waveform during which the SCR is in conduction. The angle of conduction can be changed by varying the time delay between the gate trigger pulse and the AC voltage waveform.

Changing the Angle of Conduction:
The angle of conduction can be changed by changing the gate voltage. This is because the gate voltage is used to trigger the SCR into conduction. By varying the gate voltage, the time delay between the gate trigger pulse and the AC voltage waveform can be changed, which in turn changes the angle of conduction.

Conclusion:
In conclusion, the angle of conduction in an SCR circuit can be changed by changing the gate voltage. This is because the gate voltage is used to trigger the SCR into conduction, and by varying the gate voltage, the time delay between the gate trigger pulse and the AC voltage waveform can be changed, which in turn changes the angle of conduction.