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Right answer is (b) Provide strength

The best EXPLANATION: The only use of AMPLIFIER in a CIRCUIT is to provide strength to signal. This may refer to an increase in current, voltage or power of the output w.r.t the INPUT being applied.

Correct CHOICE is (a) Watts

The explanation: Power RATING is the maximum power ALLOWABLE to dissipate by a transistor beyond this POINT transistor may behave unlikely. This is expressed in watts.

The correct option is (d) All of the mentioned

The explanation is: Power amplifier INCREASES voltage as well as current. Increase in voltage or current is small compared to normal amplifiers. But power AMPLIFICATION has OCCURRED ie. Voltage X current is more.

Right option is (d) Distortion

For explanation I WOULD say: The unwanted characteristics of amplifier OUTPUT APART from DESIRED output are collectively TERMED as distortion. This should be avoided.

The correct ANSWER is (c) Vacuum tubes

Explanation: Before the invention of POWER amplifier vacuum tubes are USED for AUDIO signal amplification which consumes large SPACE and costly.

Right choice is (C) Front END

For explanation I WOULD say: Input stage of the power amplifier is also called the front end.

Correct choice is (C) Doubled

Explanation: In the equation of power OUTPUT for the power AMPLIFIER, the power is proportional to the SQUARE of the current and inversely proportional to the resistance. If the impedance is HALVED then power is doubled.

The CORRECT answer is (a) An active DEVICE

Easiest explanation: Transistor is an active device since transistor contains VOLTAGE SOURCES which are NECESSARY for amplification.

The correct answer is (d) 2OHM

Explanation: If the RESISTANCE of the audio amplifier is LESS, the OUTPUT power of the transistor will be high since output current is INCREASING. Hence to drive a 2ohm speaker amplifier needs double power that for a 4ohm speaker.

Correct option is (b) Power lower than 100w

To elaborate: The power rating is 100 W, and that is the maximum ALLOWABLE power usage of a transistor, beyond which it may damage. If the power is LESS than 100W, the CIRCUIT operates. Near to 100W, the power may also be HIGHER than 100W, HENCE that option is incorrect.

Correct choice is (a) Class A

The EXPLANATION is: Class A amplifier has the highest LINEARITY and the lowest distortion. The amplifying element is always conducting and close to the linear portion of its transconductance curve. The point where the device is almost off is not at a zero SIGNAL point and hence its distortions compared to other CLASSES are less.

The CORRECT ANSWER is (d) K

To explain I would say: There is no amplifier called Class K. There are only A, B, C, D, E/F, G, H, S.

Right choice is (c) Class A

Explanation: Class A amplifiers are the least efficient of all. A maximum of 25% theoretical EFFICIENCY is obtainable, 50% for when using TRANSFORMER or with induced coupling. This wastes power, as well as INCREASES the cost and requires HIGHER rated output devices.

The correct option is (B) Class C

Best explanation: Class C amplifier cannot be used for audio frequency amplifiers because of its HIGH DISTORTION.

The correct choice is (a) Class D

The EXPLANATION: Class D amplifiers USE a form of PWM to control the OUTPUT devices. Conduction ANGLE varies with the pulse width and doesn’t depend on the INPUT directly. The analog signal is converted into a stream of pulses representing the signal using a modulation technique.

The correct answer is (d) CLASS B

To explain I would SAY: Class B amplifier has a theoretical EFFICIENCY of 78.5% which higher than Class A while Class D THEORETICALLY have efficiency of 100%.

The correct answer is (a) CLASS A

To elaborate: Class A AMPLIFIER has a theoretical efficiency of 50%. 50% of the ENERGY supplied is a waste.

Right OPTION is (c) DISTORTION

Easy EXPLANATION: The deviation of output from an EXACT copy of INPUT signal with amplification is collectively known as the distortion of the amplifier. They are of a different kind.

Right OPTION is (c) CLASS C

Easy explanation: Class C is the most suitable amplifier TYPE for tuning circuit and radio frequency amplification. It employs filtering and hence the FINAL signal is completely acceptable. Class C amplifiers are quite EFFICIENT than other types.

Right answer is (d) Large input SIGNAL

Explanation: Incorrect BIASING level that is, if biasing level is not properly managed improper GAIN may LEAD to distortion. Non-linear amplification is a COMMON reason for distortion in the case of transistor. If the input signal is large then output exceed the maximum peak of output that can be provided by an amplifier.

The correct OPTION is (a) SHIFT in Q-point

Explanation: If we incorrectly design our amplifier and a change in Q-point occurs, then distortion in the amplifier is observed. ALSO, if we apply too large an input signal, it MAY end up CAUSING distortion.

The CORRECT option is (a) CLIPPING

The best explanation: If amplifier OUTPUT is beyond the maximum value it cannot DISPLAY voltage further than maximum value. This CONSTITUTE clipping. This maximum output value depends on the source voltage(VCC) of the amplifier, and can’t exceed the value.

Right option is (B) Amplitude DISTORTION

The explanation is: If amplifier OUTPUT is beyond MAXIMUM value it cannot display voltage further than maximum value. This CONSTITUTE clipping and creates flat tops in the output wave. This is due to amplitude distortion in the amplifier.

Correct ANSWER is (b) Amplification

Explanation: Due to abnormalities of TRANSISTOR level of amplification VARIES with a frequency which CONSTITUTE frequency distortion.

Correct OPTION is (B) HARMONIC DISTORTION

The explanation is: The distortion happened due to the PRESENCE of harmonic frequencies in output is known as harmonic distortion.

Correct CHOICE is (d) ACTIVE elements

Best explanation: HARMONIC distortion is CAUSED by Active elements in the circuit.

Correct answer is (C) Transistor

Explanation: Harmonic distortion is caused by Active elements in the circuit. HENCE transistor is CAUSING harmonic distortion.

The correct choice is (B) SOUND quality

Easiest 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.

Right answer is (a) AMOUNT of harmonic content present in a signal

To explain I would SAY: 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.

The correct ANSWER is (d) TOTAL HARMONIC distortion

To explain: 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.

Right answer is (c) Non-linearity of amplifier

The 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.

The correct OPTION is (a) Intermodulation distortion

Easy 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.

Right answer is (c) Amount of second harmonics PRESENT in signal

Easiest 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.

Right answer is (a) √(D1^2+D2^2+D3^2+D4^2)

Explanation: RESULTANT HARMONICS is RMS VALUE of INDIVIDUAL harmonics.

Correct option is (d) cold plate

The best I can EXPLAIN: heat sink transfers thermal energy from a high-temperature MEDIUM to a low-temperature medium LIKE AIR, water etc. Usually air is used as a low-temperature medium. If water is used as medium, then it is termed as cold plate.

Correct option is (b) ALUMINUM

To ELABORATE: The thermal conductivity of aluminum is about 235 W/mK; it is the cheapest and lightweight metal. Aluminum HEAT sinks are also CALLED extruded heat sinks because they can be made using the EXTRUSION technique.

Correct choice is (c) Do not possess mechanical components

The explanation: Unlike active heat sink passive heat sink do not possess any mechanical component and are MADE of ALUMINUM finned radiator. Thus these passive heat sinks are cheaper than the active ones and only USE convection to dissipate thermal energy. They are more RELIABLE since they have no moving PARTS but the performance of active sinks is better in dissipating heat.

Right answer is (d) ALUMINUM heat SINK

Explanation: The more durable heat sink AMONG this is aluminum heat sink.

The correct choice is (d) Extrusion heat sink

To explain I would SAY: Aluminum heat sinks are also called as EXTRUDED heat sinks as they can be made using extrusion. Aluminum is the most common heat sink MATERIAL, light in weight and costs less than Cu and other materials, and has RELATIVELY good thermal conductivity.

Correct choice is (a) Stamped heat sink

The BEST explanation: Stamped heat sinks are made of metal that is stamped to FORM a PARTICULAR shape. These are cheaper compared to extruded heat sinks. These are used for low-power APPLICATIONS and hence these are low in PERFORMANCE.

Correct option is (d) None of the mentioned

Easiest explanation: The performance of the heat SINK DEPENDS on the factors like the choice of material, protrusion design, surface treatment and air velocity. The material is PREFERRED to have high conductivity and heat absorption. The shape and design also effect heat FLOW as well as coolant flow in the sink.