The SCR shuts itself off when:
A. current flows through it.
B. the anode voltage is negative.
C. voltage is applied to the gate while the anode is positive.
D. voltage is removed from the gate when the anode is positive.

The SCR truns itself on when:
A. voltage is connected between the anode and cathode.
B. AC current is used.
C. voltage is applied to the gate while the anode is positive.
D. voltage is removed from the gate when the anode is positive.

The SCR in the lamp dimmer controls the lamp intensity by:
A. varying its resistance to the flow of current.
B. lowering the voltage of the power source.
C. turning the current on and off.
D. changing the frequency of the AC.

The capacitor in the lamp dimmer circuit charges:
A. faster when the potentiometer is set for a low resistance
B. only when the SCR is off.
C. 60 times every second.
D. all of the above.

The letters, SCR, stand for:
A. Silicon Controlled Resistor.
B. Safety Controlled Rectifier.
C. Silver Contact Rectifier.
D. Silicon Controlled Rectifier.

TRUE OR FALSE

1. The SCR dimmer circuit works on AC or DC.
2. The SCR turns off when the voltage across it gets negative.
3. The lamp is constantly blinking on and off but at a speed that makes it difficult to see.
4. The potentiometer in the circuit has a large current flowing through it.
5. In this dimmer circuit, a small current is switching a large current.

 

As is the point of learning, I will point you in the direction of a few good resources on Silicon Controlled Rectifiers (SCRs):

All About Circuits: SCRs

Wikipedia: SCRs

And

Play-Hookey: SCRs

Try answering the question and post you answers here, I'm sure someone will check them to see if they are right for you.