# Analog Circuits Questions and Answers – Distortion in Amplifier – 2

This set of Analog Circuits online test focuses on “Distortion in Amplifier – 2”.

1. THD+N is a scale used to expressing _______ of an audio amplifier.
a) Gain
b) Sound quality
c) Amplification factor
d) Distortion

Explanation: THD+ N refers to Total Harmonic Distortion plus Noise. It is a much more comparable quantity between different devices. It can be used to express the quality of an audio amplifier and is measured using a distortion analyzer.

2. THD is a measure of ____________
a) Amount of harmonic content present in a signal
b) Amount of output power
c) Total amount of distortion
d) Total amount of amplitude distortion

Explanation: THD (Total Harmonic Distortion) is a measurement of the harmonic distortion present in a signal. It is the ratio of sum of power of all harmonic components to the power of the fundamental frequency of the signal.

3. The ratio of the RMS amplitude of the higher order harmonic frequencies to the RMS amplitude of the fundamental frequency is commonly called __________
a) Total harmonic power
b) Total amplitude distortion
c) Total frequency distortion
d) Total harmonic distortion

Explanation: THD is the ratio of RMS amplitude of higher order harmonic frequencies to the RMS amplitude of the fundamental frequency. THD is expressed in percentage.

4. Intermodulation distortion is caused by __________
a) Presence of harmonic components in signal
b) Non- linearity of biasing circuit
c) Non-linearity of amplifier
d) High frequency signal

Explanation: Intermodulation is the amplitude modulation of signals containing two or more frequencies, and this is caused by non-linearity of the system. Intermodulation of frequencies will form additional unwanted components at multiple frequencies. It can also give rise to spurious emissions in radio transmission, often in form of sidebands.

5. The ratio of the RMS value of additional frequency components in output to the RMS value of the original output of the amplifier is called __________
a) Intermodulation distortion
b) Total amplitude distortion
c) Total frequency distortion
d) Total harmonic distortion

Explanation: The ratio of the RMS value of additional frequency components in output to the RMS value of the original output of the amplifier is known as intermodulation distortion. These additional frequency components can be harmonics, as well as sums and differences of the original frequencies, as well as the sum and differences of the harmonics.
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6. Second order harmonic distortion is __________
a) Amount of second harmonics and first harmonics in signal
b) Amount of second harmonics and fourth harmonics in signal
c) Amount of second harmonics present in signal
d) RMS value of all even harmonics in signal

Explanation: Second harmonic distortion is the amount of second harmonic signal present in signal. It is important since second harmonic is most troublesome among other harmonics.

7. Power delivered to load is _________ with an increase in harmonic distortion.
a) Increases
b) Decreases
c) Constant
d) Cannot predict

Explanation: The equation of output power (Pac)D = Pac (1+D2). It is clear that output power increases with distortion.

8. In three-point method the harmonics which are considered for calculating distortion is __________
a) First harmonics only
b) First and Second harmonics only
c) First, Second and Third harmonics only
d) Second and Third harmonics only

Explanation: In three-point method, the distortion due to first and second harmonics are considered.

9. If D1, D2, D3, D4 are the distortion produced by second, third, fourth, fifth respectively (others are insignificant). Then total harmonic distortion is __________
a) √(D12+D22+D32+D42)
b) √(D12+D32)
c) √(D22+D42)
d) √(D12+D22)

Explanation: Resultant harmonics is RMS value of individual harmonics.

10. Power delivered to load calculated by five-point method can be equal to __________
(Pac is power delivered to load without distortion and D is the RMS of all Harmonic distortion)
a) Pac (1-D2)
b) Pac/D2
c) Pac (1+D2)
d) Pac D2

Explanation: The equation of power delivered to load is same whether it is calculated by three-point or five point. The only difference is the calculation of D.

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