A Quiz On Power Electronics

Explanation
An SCR is a device with 3 junctions. This means that it consists of three layers of semiconductor material, each forming a junction with the adjacent layer. The three junctions are known as the P-N-P-N structure, where P represents the positive or anode layer and N represents the negative or cathode layer. The middle N layer acts as a gate, controlling the flow of current between the anode and cathode. Therefore, the correct answer is that an SCR is a device with 3 junctions.

Explanation
SCR stands for Silicon Controlled Rectifier, which is a type of semiconductor device that can control the flow of electric current. It is commonly used in speed control of DC motors because it can handle high currents and voltages, making it suitable for controlling the power supplied to the motor. By adjusting the triggering angle of the SCR, the average voltage and hence the speed of the motor can be controlled. FET and NPN transistors are not typically used for speed control of DC motors.

Explanation
A chopper is an electronic device that can convert a fixed DC voltage into a variable DC voltage. It uses switching techniques to control the voltage output. By adjusting the duty cycle of the switching signal, a chopper can step up or step down the DC voltage. Therefore, it is possible to use a chopper to step up a DC voltage, making the statement true.

Explanation
A dc chopper is an electronic circuit that converts a fixed DC voltage into a variable DC voltage. It achieves this by chopping the fixed DC voltage into a series of on and off pulses, which are then filtered to obtain the desired variable DC output voltage. Therefore, a dc chopper does indeed convert directly from DC to DC, making the statement true.

Explanation
A triac is a three-terminal bidirectional switch because it can conduct current in both directions. It can be triggered to turn on and off by a small current applied to its gate terminal, allowing it to control the flow of alternating current (AC) in both positive and negative half cycles. The bidirectional nature of the triac makes it suitable for applications such as dimmer switches, motor speed control, and AC power control.