21. The knee voltage of a diode is approximately equal to the

A. Applied voltage

B. Barrier potential

C. Breakdown voltage

D. Forward voltage

E. None of the above

22. A Zener regulator has an input voltage from 15 to 20 V and a load current from 5 to 20 mA. If the zener voltage is 6.8 V, what value should the series resistor have?

A. 310 Ohm

B. 400 Ohm

C. 410 Ohm

D. 550 Ohm

E. None of the above

23. The rms value of a sine waveform is:

A. the number of cycles completed in one second

B. the time required to complete one full cycle

C. equal to 0.707 times the peak amplitude

D. equal to 1.41 times the peak amplitude

E. None of the above

24. Which one of the following is a direct statement of Ohm’s law?

A. The voltage drop across a resistance is proportional to the value of resistance and the amount of current flowing through it

B. The total resistance of a parallel circuit is less than the value of the smallest resistance

C. The algebraic sum of voltages in a loop is equal to zero

D. The algebraic sum of currents entering and leaving a point is equal to zero

E. None of the above

25. A high-pass filter:

A. passes lower-frequency signals and reduces higher-frequency signals

B. passes higher-frequency signals and reduces lower-frequency signals

C. has no effect on ac signals

D. increases the level of all frequencies by a significant amount

E. None of the above