set-2

151. A Wien bridge oscillator uses ______ feedback.

1. Only positive

2. Only negative

3. Both positive and negative

4. None of the above

Show me the answer

Answer: 3. Both positive and negative

Explanation:

• A Wien bridge oscillator uses both positive and negative feedback to achieve stable oscillations.

• Therefore, the correct answer is Both positive and negative.

152. The piezoelectric effect in a crystal is ______.

1. A voltage developed because of mechanical stress

2. A change in resistance because of temperature

3. A change in frequency because of temperature

4. None of the above

Show me the answer

Answer: 1. A voltage developed because of mechanical stress

Explanation:

• The piezoelectric effect in a crystal refers to the generation of a voltage when mechanical stress is applied.

• Therefore, the correct answer is A voltage developed because of mechanical stress.

153. If the crystal frequency changes with temperature, we say that crystal has ______ temperature coefficient.

1. Positive

2. Zero

3. Negative

4. None of the above

Show me the answer

Answer: 1. Positive

Explanation:

• If the crystal frequency increases with temperature, it has a positive temperature coefficient.

• Therefore, the correct answer is Positive.

154. The crystal oscillator frequency is very stable due to ______ of the crystal.

1. Rigidity

2. Vibrations

3. Low Q

4. High Q

Show me the answer

Answer: 4. High Q

Explanation:

• The high Q factor of a crystal ensures very stable frequency generation in a crystal oscillator.

• Therefore, the correct answer is High Q.

155. An oscillator differs from an amplifier because it ______.

1. Has more gain

2. Requires no input signal

3. Requires no D.C. supply

4. Always has the same input

Show me the answer

Answer: 2. Requires no input signal

Explanation:

• An oscillator generates its own output signal without requiring an external input signal, unlike an amplifier.

• Therefore, the correct answer is Requires no input signal.

156. For an oscillator to properly start, the gain around the feedback loop must initially be ______.

1. 1

2. Greater than 1

3. Less than 1

4. Equal to attenuation of feedback circuit

Show me the answer

Answer: 2. Greater than 1

Explanation:

• For an oscillator to start, the gain around the feedback loop must initially be greater than 1 to build up oscillations.

• Therefore, the correct answer is Greater than 1.

157. A class A power amplifier uses ______.

1. Two transistors

2. One transistor

3. Three transistors

4. Four transistors

Show me the answer

Answer: 2. One transistor

Explanation:

• A class A power amplifier typically uses one transistor to amplify the entire input signal cycle.

• Therefore, the correct answer is One transistor.

158. The maximum efficiency of resistance loaded class A power amplifier is ______.

1. 5%

2. 35%

3. 25%

4. 50%

Show me the answer

Answer: 3. 25%

Explanation:

• The maximum efficiency of a resistance-loaded class A power amplifier is 25%.

• Therefore, the correct answer is 25%.

159. The maximum efficiency of transformer coupled class A power amplifier is ______.

1. 50%

2. 25%

3. 30%

4. 5%

Show me the answer

Answer: 1. 50%

Explanation:

• The maximum efficiency of a transformer-coupled class A power amplifier is 50%.

• Therefore, the correct answer is 50%.

160. Power amplifiers handle ______ signals compare to voltage amplifiers.

1. Small

2. Large

3. Very small

4. Equal

Show me the answer

Answer: 2. Large

Explanation:

• Power amplifiers handle large signals compared to voltage amplifiers, which handle small signals.

• Therefore, the correct answer is Large.

161. In class A operation, the operating point is generally located ______ of the D.C. load line.

1. At cut off point

2. At the middle

3. At saturation point

4. In active region

Show me the answer

Answer: 2. At the middle

Explanation:

• In class A operation, the operating point is generally located at the middle of the D.C. load line to allow maximum symmetrical swing.

• Therefore, the correct answer is At the middle.

162. A power amplifier has comparatively ______ β.

1. Small

2. Large

3. Very large

4. Same

Show me the answer

Answer: 1. Small

Explanation:

• A power amplifier typically has a small β (current gain) because it is designed to handle large currents and power.

• Therefore, the correct answer is Small.

163. A class A power amplifier is sometimes called ______ amplifier.

1. Reciprocating

2. Single - ended

3. Symmetrical

4. Differential

Show me the answer

Answer: 2. Single - ended

Explanation:

• A class A power amplifier is sometimes called a single-ended amplifier because it uses a single transistor to amplify the entire input signal cycle.

• Therefore, the correct answer is Single - ended.

164. When no signal is applied, the approximate collector efficiency of class A power amplifier is ______.

1. 25%

2. 10%

3. 0%

4. 50%

Show me the answer

Answer: 3. 0%

Explanation:

• When no signal is applied, the collector efficiency of a class A power amplifier is 0% because no useful power is delivered to the load.

• Therefore, the correct answer is 0%.

165. The maximum A.C. power output from a class A power amplifier is 10 W. What should be the minimum power rating of the transistor used?

1. 20W

2. 5 W

3. 25W

4. 50W

Show me the answer

Answer: 1. 20W

Explanation:

• The minimum power rating of the transistor should be at least twice the maximum A.C. power output to handle peak power demands.

• Therefore, the correct answer is 20W.

166. The most costly coupling is ______ coupling.

1. Transformer

2. Impedance

3. RC

4. Direct

Show me the answer

Answer: 1. Transformer

Explanation:

• Transformer coupling is the most costly due to the complexity and cost of the transformer.

• Therefore, the correct answer is Transformer.

167. Where does the Q point lie for class B amplifier?

1. Active

2. Cut off

3. Saturation

4. Between saturation and active

Show me the answer

Answer: 2. Cut off

Explanation:

• In a class B amplifier, the Q point lies at cut off to allow each transistor to conduct for only half of the input signal cycle.

• Therefore, the correct answer is Cut off.

168. What happens when class B amplifier is in a quiescent state?

1. No current flows through the transistor

2. Maximum current flows through the transistor

3. Half of the maximum current flows through the transistor

4. Quarter of the maximum current flows

Show me the answer

Answer: 1. No current flows through the transistor

Explanation:

• In the quiescent state of a class B amplifier, no current flows through the transistor because the Q point is at cut off.

• Therefore, the correct answer is No current flows through the transistor.

169. What is the value of the maximum efficiency of the class B amplifier?

1. 25%

2. 35%

3. 35% to 50%

4. 50% to 70%

Show me the answer

Answer: 4. 50% to 70%

Explanation:

• The maximum efficiency of a class B amplifier is 50% to 70%, depending on the design and load conditions.

• Therefore, the correct answer is 50% to 70%.

170. What kind of design is used to avoid transformer usage?

1. High resistance

2. Matched load

3. Complementary symmetry

4. Capacitive Model

Show me the answer

Answer: 3. Complementary symmetry

Explanation:

• Complementary symmetry design is used to avoid the need for a transformer in class B amplifiers.

• Therefore, the correct answer is Complementary symmetry.

171. What is cross over distortion?

1. Effect occurred during switching of transistor after every half cycle

2. Distortion occurred due to resistors

3. Distortion occurred due to Capacitors

4. Distortion occurred due to Inductors

Show me the answer

Answer: 1. Effect occurred during switching of transistor after every half cycle

Explanation:

• Cross over distortion occurs during the switching of transistors in a class B amplifier when one transistor turns off and the other turns on.

• Therefore, the correct answer is Effect occurred during switching of transistor after every half cycle.

172. How to avoid cross over distortion?

1. By using more resistance

2. By using more capacitance

3. By using more Inductance

4. By shifting the Q point above cut off

Show me the answer

Answer: 4. By shifting the Q point above cut off

Explanation:

• Cross over distortion can be avoided by shifting the Q point slightly above cut off, which is done in class AB amplifiers.

• Therefore, the correct answer is By shifting the Q point above cut off.

173. For a Class B amplifier, the utilized load power is 300W and the Dc power is 500W, find efficiency.

1. 30%

2. 60%

3. 90%

4. 100%

Show me the answer

Answer: 2. 60%

Explanation:

• The efficiency is given by: $\eta = \frac{\text{Load Power}}{\text{DC Power}} \times 100 = \frac{300}{500} \times 100 = 60\%$

• Therefore, the correct answer is 60%.

174. What is the conduction angle for Class B push-pull amplifier?

1. 0°

2. 90°

3. 180°

4. 270°

Show me the answer

Answer: 3. 180°

Explanation:

• In a class B push-pull amplifier, each transistor conducts for 180° of the input signal cycle.

• Therefore, the correct answer is 180°.

175. A power transistor is a ______.

1. Three layer, three junction device

2. Three layer, two junction device

3. Two layer, one junction device

4. Four layer, three junction device

Show me the answer

Answer: 2. Three layer, two junction device

Explanation:

• A power transistor is a three-layer, two-junction device (e.g., NPN or PNP).

• Therefore, the correct answer is Three layer, two junction device.

176. For a power transistor, if base current IB is increased keeping Vcc constant; then ______.

1. Ic increases

2. Ic decreases

3. Ic remains constant

4. Ic changes sinusoidal

Show me the answer

Answer: 1. Ic increases

Explanation:

• In a power transistor, increasing the base current ($I_B$) while keeping $V_{CC}$ constant causes the collector current ($I_C$) to increase.

• Therefore, the correct answer is Ic increases.

177. Insulated-gate bipolar transistor (IGBT) has combinational advantages of ______.

1. BJTs and SITs

2. BJTs and MOSFETs

3. SITs and MOSFETs

4. FETs and BJTs

Show me the answer

Answer: 2. BJTs and MOSFETs

Explanation:

• An IGBT combines the advantages of BJTs (high current handling) and MOSFETs (high input impedance).

• Therefore, the correct answer is BJTs and MOSFETs.

178. A Gate Turn Off (GTO) can be turned on by applying ______.

1. Positive gate signal

2. Positive drain signal

3. Positive source signal

4. Negative source signal

Show me the answer

Answer: 1. Positive gate signal

Explanation:

• A GTO can be turned on by applying a positive gate signal.

• Therefore, the correct answer is Positive gate signal.

179. The turn on time of an SCR with inductive load is 20 μs. The pulse train frequency is 2.5 KHz with a mark/space ratio of 1/10, and then SCR will ______.

1. Turn On

2. Not turn on

3. Turn on if inductance is removed.

4. Turn on if pulse frequency is increased to two times

Show me the answer

Answer: 1. Turn On

Explanation:

• With a pulse train frequency of 2.5 KHz and a mark/space ratio of 1/10, the SCR will turn on because the pulse duration is sufficient to trigger the SCR.

• Therefore, the correct answer is Turn On.

180. What are the three terminals of a power MOSFET called?

1. Collector, emitter, Gate

2. Drain, source, gate

3. Collector, emitter, base

4. Drain, emitter, base

Show me the answer

Answer: 2. Drain, source, gate

Explanation:

• A power MOSFET has three terminals: Drain, Source, and Gate.

• Therefore, the correct answer is Drain, source, gate.

181. A thyristor can be termed as ______.

1. AC switch

2. DC switch

3. Wave switch

4. Square wave switch

Show me the answer

Answer: 2. DC switch

Explanation:

• A thyristor is primarily used as a DC switch because it can control DC power by turning on and off.

• Therefore, the correct answer is DC switch.

182. In a series R-L-C circuit at resonance ______.

1. $\omega LC = 1$

2. $\omega L^2 C^2 = 1$

3. $\omega^2 LC = 1$

4. $\omega^2 L^2 C = 1$

Show me the answer

Answer: 3. $\omega^2 LC = 1$

Explanation:

• At resonance in a series R-L-C circuit, the condition is: $\omega^2 LC = 1$

• Therefore, the correct answer is $\omega^2 LC = 1$.

183. The power factor of a series R-L-C circuit at its half-power points is ______.

1. Unity

2. Lagging

3. Leading

4. Lagging or leading

Show me the answer

Answer: 4. Lagging or leading

Explanation:

At the half-power points of a series R-L-C circuit, the power factor can be either lagging or leading, depending on whether the frequency is below or above resonance. Therefore, the correct answer is Lagging or leading.