1.What happens to capacitative reactance when operating frequency is increased?
a) Increases
b) Decreases
c) Remains constant
d) goes to infinite
Explanation: Capacitative reactance is inversely proportional to the operating frequency and is given by the formula Xc= 1/2πfC where C is the capacitance value in Farad.
2. Calculate the reactance of a 100-pF capacitor at an operating frequency of 2 MHz?
a) 200Ω
b) 700.16Ω
c) 796.2Ω
d) 2Ω
Explanation: Capacitative reactance =Xc= 1/2πfC = 1/(2 x 3.14 x 2 x 106 x 100 x 10-12) = 796.2Ω.
3. Which one of the following is false with respect to stray capacitance?
a) Reduces with decrease in size of lead wires
b) Reduces when chip capacitors are used
c) Increases when lead wires a are lengthy
d) Increases with less capacitance value
Explanation: The lead wires of capacitors behave as a complex RLC circuit and generate stray capacitance. This can be reduced by shortening the length of the lead wires or using chip capacitors. However, decreasing or increasing the value of capacitance does not affect stray capacitance.
4. What happens to inductive resistance when operating frequency is increased?
a) Increases
b) Decreases
c) Remains constant
d) Goes to infinite
Explanation: Inductive reactance is directly proportional to the operating frequency and is given by the formula Xf= 2πfL where L is the inductance value in Henry.
5. What is the inductive reactance of a 40-μH coil at 18 MHz?
a) 4000Ω
b) 4522Ω
c) 4522H
d) 0
Explanation: Inductive reactance = XL=2πfL = 2 x 3.14 x 18 x 106 x 40 x 10-6 = 4522Ω.
6. What is the Q factor for a 3-μH inductor with a total resistance of 45Ω at 90 MHz?
a) 37.68
b) 37.68Ω
c) 29.22Ω
d) 32.75Ω
Explanation: Quality factor = Q = 2πfL/R = (2 x 3.14 x 90 x 106 x 3 x 10-6)/45 = 1695.6 / 45 = 37.68.
7. What is the resonant frequency of a 2.7-pF capacitor and a 33-nH inductor?
a) 512MHz
b) 720GHz
c) 250MHz
d) 533MHz
Explanation:
8. What is the bandwidth of a resonant circuit with a frequency of 28 MHz and a Q of 80?
a) 350KHz
b) 30KHz
c) 42.7KHz
d) 57.05MHz
Explanation: Bandwidth = resonant frequency / Quality factor = 28 x 106 /80 = 350KHz.
9.What is a filter?
a) Frequency selective circuit
b) Amplitude selective circuit
c) Frequency damping circuit
d) Amplitude damping circuit
Explanation: A filter is a frequency-selective circuit. Filters are designed to pass some frequencies and reject others. Filters are used to reduce noise and increase selectivity
10. What are filters created by using resistors and capacitors or inductors and capacitors called?
a) Active filters
b) Passive filters
c) Continuous filters
d) Differential filters
Explanation: Simple filters created by using resistors and capacitors or inductors and capacitors are called passive filters because they use passive components that do not amplify. In communication work, many filters are of the passive LC variety, although many other types are used.