21 3-24.   The SCR is equivalent to what electronic device? 1.    Diode   2.    Tetrode   3.    Thyratron   4.    Beam power tube 3-25.   Which of the following circuits uses an SCR in its electronic circuitry? 1.    Computer logic circuit   2.    Voltage comparator circuit   3.    Antenna power amplifier circuit   4.    Each of the above Figure 3C. The schematic symbol for the SCR. IN ANSWERING QUESTION 3-26, REFER TO FIGURE 3-C.   3-26.   What is the impedance between points A and C (a) when the SCR is biased off and (b) when the SCR is at saturation?   1. (a) Low (b) low   2. (a) Low (b) high   3. (a) High (b) high   4. (a) High (b) low Figure 3D. A two-transistor circuit. IN ANSWERING QUESTION 3-27, REFER TO FIGURE 3-D. 3-27.   When a positive current is applied to the gate lead, what happens to the collector current of Q1 and Q2? 1.    Increases to a value limited only by the external circuit   2.    Increases to a value limited only by the internal circuit   3.    Decreases to a value limited only by the external circuit   4.    Decreases to a value limited only by the internal circuit 3-28.   Once an SCR is turned on by a positive pulse of current applied to the gate lead, what action turns the SCR off?   1.    Removing the positive pulse from the gate lead   2.    Inserting a negative pulse of current on the gate lead   3.    Reducing the collector current to a value below that necessary to maintain conduction   4.    Increasing the collector current to a point that the SCR will go into saturation and cut off 3-29.   What is the total number of terminals in a TRIAC?   1.    One   2.    Two   3.    Three   4.    Four