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Correct choice is (b) 80.3%

BEST 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 = ((π^2 / 6) – 1)^1/2 = 0.803 = 80.3%.

The correct ANSWER is (c) By using MATCHED TRANSFORMERS as load

Best explanation: We can increase the efficiency of CLASS A amplifier by using load matching concept, HENCE a pair of matched transformer can be used as load which in turn increases the efficiency.

The correct ANSWER is (a) 48.3%

The 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 = ((π^2 / 8) – 1)^1/2 = 0.483 = 48.3%.

Correct choice is (c) 12.1%

The best I can explain: 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 = ((π^4 / 96) – 1)^1/2 = 0.121 = 12.1%.

Correct option is (a) True

To explain: 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.

Right answer is (a) CLASS A

Easy explanation: Class A configuration has the highest linearity due to which is produces the least amount of distortion, which in turn produces EVEN lower second order harmonic distortion. It is then followed by Class AB, Class B and Class C.

Right answer is (a) 0.8

The explanation is: To CALCULATE the SNR (signal to noise RATIO) we TAKE the ratio of the input signal amplitude to the output signal amplitude.

SNR = input wave / output wave = 20DB / 25dB = 0.8

Correct option is (d) TRANSISTOR switch arrays

To EXPLAIN: The SECOND harmonic DISTORTION can be reduced by transistor switch arrays. The switch arrays are implemented in a pseudo-differential CONFIGURATION. This design of the transistor switch arrays as a side effect reduces the second harmonic distortion.

Correct option is (d) 100HZ

For explanation I would say: The harmonics of a WAVE are the INTEGER multiples of the fundamental frequency. HENCE, the SECOND harmonics of a wave with fundamental frequency 50Hz is 100Hz.

Second harmonics = 2 × fundamental frequency = 2 × 50Hz = 100Hz

Correct option is (d) Switching TRANSISTOR theory

For explanation I would SAY: The class A amplifier is the simplest form of POWER amplifier that uses the switching transistor in the STANDARD common emitter configuration.

Right option is (c) 250HZ

The 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.

Right option is (b) dBc

For EXPLANATION: The second order harmonic distortion is the ratio of second-order harmonic to the INPUT SIGNAL or the carrier signal. It is measured as dBc. dBc is the POWER ratio of a signal to a carrier signal, expressed in decibels.

Correct answer is (c) Non-linearity of TRANSISTORS

Easy explanation: HARMONIC DISTORTION in a power amplifier is caused due to the non-linearity of transistor devices. Transistors are the active elements in the circuit and are USED for amplification. However, they do not EQUALLY amplify each point of the input wave form which then creates distortion.

The CORRECT CHOICE is (a) 30 or less

To explain: Since in Class A amplifiers distortion is more and as it requires TUNED circuit as load, the efficiency is very low.

The CORRECT ANSWER is (a) Increases

For 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.

Right OPTION is (c) 11.25dB

The EXPLANATION is: The total HARMONIC distortion is calculated by the FORMULA given below. Given the first harmonic distortion V1 = 20dB, V2 = 25dB and N = 10dB:

THD = (V2^2 + V3^2 + … + Vn^2)^1/2 / V1 = (V2^2)^1/2 / V1 = V2 / V1 = 25 / 20 = 1.25

THD + N = 1.25 + 10 = 11.25dB.

The CORRECT OPTION is (d) 360

For explanation: Since the AMPLIFIER is always On, it conducts all the CURRENT waveform which can be USED to state that it has 360 degree conduction angle.

Correct answer is (c) Higher 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.

Correct CHOICE is (a) They are weak against distortions

The best I can explain: Since class A amplifiers use basic TRANSISTOR, even the NOISE signal will GET amplified when the noise signal exists in INPUT.

The correct answer is (c) 1.25

The best explanation: The TOTAL HARMONIC distortion is calculated by the formula given below. Given the first harmonic distortion V1 = 20DB and V2 = 25dB:

THD = (V2^2 + V3^2 +…+ Vn^2)^1/2 / V1 = (V2^2)^1/2 / V1 = V2 / V1 = 25 / 20 = 1.25

The correct choice is (a) True

For explanation: All audio amplifiers produce a certain level of distortion USUALLY in the form of EVEN harmonics. Out of all the even harmonics, the most prominent one is the SECOND order harmonics. Second order HARMONIC distortion is the amount of 2nd order harmonic content present in the output signal with respect to the fundamental FREQUENCY.