1.Which one of the following is not a type of modulation?
a) Frequency modulation
b) Amplitude Modulation
c) Pulse modulation
d) Phase amplitude modulation
Explanation: Modulation is of three types, frequency modulation, amplitude modulation and phase modulation. Pulse modulation is a type of amplitude modulation.
2. In amplitude modulation, which of the following varies?
a) Frequency of the carrier
b) Frequency of the information signal
c) Amplitude of the carrier wave
d) Amplitude of the information signal
Explanation: In amplitude modulation, the amplitude of the carrier wave is modulated with respect to the information signal. The frequency and the phase of both the carrier and the information signal remain constant.
3. You have 5 information signals and only one transmitter. What technique will help in transmitting all the 5 signals?
a) Frequency modulation
b) Multiplexing
c) Amplification
d) Amplitude modulation
Explanation: Multiplexing is the process of transmitting more than one signal via a common transmitting medium. A device called a multiplexer is used for this purpose. The signal can be demultiplexed at the receiver end to retrieve the original information.
4. What type of multiplexing is used in mobile phones?
a) Frequency division multiplexing
b) Time division multiplexing
c) Code division multiplexing
d) Phase multiplexing
Explanation: In code-division multiplexing, the signals to be transmitted are converted to digital data that is then uniquely coded with a faster binary code. The signals modulate a carrier on the same frequency. All use the same communications channel simultaneously. The unique coding is used at the receiver to select the desired signal.
5. Which one of the following is not true with respect to amplitude modulation?
a) Less noise
b) Longer range
c) Lower bandwidth
d) Less complex circuits
Explanation: Although AM is much simpler and has a wider range due to atmospheric propagation, one of its major disadvantages is due to noise. Noise directly affects the amplitude of the signal and its hard to retrieve the original information
6. What type of multiplexing is used in serial buses?
a) Time division multiplexing
b) Code division multiplexing
c) Frequency division multiplexing
d) Phase multiplexing
Explanation: In serial buses, time division multiplexing is used to split the digital data, which is in binary numbers, into individual bits which occupy a particular time slot and is transmitted. The use of serial buses increases the limit on transmission speed and reduces noise.
7. What is reactance?
a) Resistance offered to ac current by resistor only
b) Resistance offered to dc current by resistor
c) Resistance offered to ac current by coil and capacitance
d) Resistance offered to dc current by coil and capacitance
Explanation: Both coils and capacitors offer an opposition to alternating current flow known as reactance, which is expressed in ohms. Like resistance, reactance is an opposition that directly affects the amount of current in a circuit.
8. What happens to the current when it passes through a capacitor?
a) Phase of voltage leads the current
b) Phase of current leads the voltage
c) Phase of current and voltage cancel out each other
d) Phase of current and voltage gets added
Explanation: In addition to resistance of alternating current flow, a capacitor alters the phase difference between the current and voltage. The capacitor lowers the phase of the voltage and hence the current leads the voltage.
9. What happens to the voltage when it passes through an inductor/coil?
a) Phase of voltage leads the current
b) Phase of current leads the voltage
c) Phase of current and voltage cancel out each other
d) Phase of current and voltage gets added
Explanation: In addition to a resistance of alternating current flow, an inductor/coil alters the phase difference between the current and voltage. The inductor/coil lowers the phase of the current and hence the voltage leads the current.
10. A capacitor used in an ac circuit continually charges and discharges.
a) True
b) False
Explanation: In an ac power supply the voltage increases and decreases with a particular frequency. During the first half cycle, the capacitor gets charged and in the other half, it gets discharged. The same process repeats throughout the wave.