# Electronic Devices and Circuits Questions and Answers – Higher-Order Harmonic Distortion

This set of Electronic Devices and Circuits Multiple Choice Questions & Answers (MCQs) focuses on “Higher-Order Harmonic Distortion”.

1. What does THD+N represent in higher order harmonic distortion?
a) Noise
b) Higher order distortion
c) Higher order distortion with noise component
d) Second order distortion with noise component

Explanation: THD+N represents the addition of all noise components to the fundamental frequency. Subsequently noise is also accounted for in this scale, hence it is better than the THD scale. The cause for noise being present in the amplifier output includes the power supply interference, RF interference, switching noises and many more.

2. What is the higher order harmonics of order 5 of a wave form with fundamental frequency of 50Hz?
a) 50Hz
b) 150Hz
c) 250Hz
d) 100Hz

Explanation: The harmonics of a wave are the integer multiples of the fundamental frequency. Hence, the fifth harmonics of a wave with fundamental frequency 50Hz is 250Hz.
Fifth harmonics = 5 × fundamental frequency = 5 × 50Hz = 250Hz.

3. Lower order harmonics are harder to hear compared to the higher order harmonics.
a) True
b) False

Explanation: All audio amplifiers produce a certain level of distortion usually in the form of even harmonics. Out of all the even harmonics, lower order harmonics are harder to hear compared to the higher order harmonics.

4. What is the total harmonic distortion if the amplitude of first harmonic distortion is 20dB, second harmonic distortion 25dB and external noise is 10dB?
a) 11.2dB
b) 11.52dB
c) 11.25dB
d) 11.5dB

Explanation: The total harmonic distortion is calculated by the formula given below. Given the first harmonic distortion V1 = 20dB, V2 = 25dB and N = 10dB:
THD = (V22 + V32 + … + Vn2)1/2 / V1 = (V22)1/2 / V1 = V2 / V1 = 25 / 20 = 1.25
THD + N = 1.25 + 10 = 11.25dB.

5. What is the value of a THDF for a square wave?
a) 48.3%
b) 80.3%
c) 12.1%
d) 37.0%

Explanation: The THDF values of certain standard waveforms are calculated diagnostically. To compute the THDF for a square wave, we use the formula given below:
THDF = ((π2 / 8) – 1)1/2 = 0.483 = 48.3%.
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6. What happens to the gap between THDF and THDR for higher order harmonic distortion?
a)Increases
b) Decreases
c) Remains unchanged
d) Not related

Explanation: THDF represents the total harmonic distortion for fundamental frequency and THDR represents the total harmonic distortion for root mean square. For lower harmonics, the gap between these two values is negligible. However, for higher order harmonics the gap increases.

7. What is the value of a THDF for a sawtooth wave?
a) 48.3%
b) 80.3%
c) 12.1%
d) 37.0%

Explanation: The THDF values of certain standard waveforms are calculated diagnostically. To compute the THDF for a sawtooth wave, we use the formula given below:
THDF = ((π2 / 6) – 1)1/2 = 0.803 = 80.3%.

8. What is the value of a THDF for a symmetrical triangle wave?
a) 48.3%
b) 80.3%
c) 12.1%
d) 37.0%

Explanation: The THDF values of certain standard waveforms are calculated diagnostically. To compute the THDF for a symmetrical triangle wave, we use the formula given below:
THDF = ((π4 / 96) – 1)1/2 = 0.121 = 12.1%.

Sanfoundry Global Education & Learning Series – Electronic Devices and Circuits. 