> For the complete documentation index, see [llms.txt](https://nec-license.gitbook.io/books/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://nec-license.gitbook.io/books/1.-concept-of-basic-electrical-and-electronics-engineering/mcqs/mcqs-on-basic-electronics/set-2.md).
# 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**.