> 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-1.md).
# set-1
### 80. How does a semiconductor behave at absolute zero?
1. Conductor
2. Insulator
3. Semiconductor
4. Protection device
Show me the answer
**Answer:** 2. Insulator
**Explanation:**
* At absolute zero (0 K), the electrons in a semiconductor are in their lowest energy state and cannot move freely.
* Therefore, the semiconductor behaves as an **insulator**.
* The correct answer is **Insulator**.
### 81. Semiconductor acts as an insulator in the presence of impurities.
1. True
2. False
Show me the answer
**Answer:** 2. False
**Explanation:**
* Semiconductors become **conductive** when doped with impurities, as the impurities introduce free charge carriers (electrons or holes).
* Therefore, the statement is **False**.
### 82. How is the resistance of semiconductor classified?
1. High resistance
2. Positive temperature co-efficient
3. Negative temperature co-efficient
4. Low resistance
Show me the answer
**Answer:** 3. Negative temperature co-efficient
**Explanation:**
* The resistance of a semiconductor **decreases** with an increase in temperature, which is known as a **negative temperature coefficient**.
* Therefore, the correct answer is **Negative temperature co-efficient**.
### 83. What are the charge carriers in semiconductors?
1. Electrons and holes
2. Electrons
3. Holes
4. Charges
Show me the answer
**Answer:** 1. Electrons and holes
**Explanation:**
* In semiconductors, the charge carriers are **electrons** (negative charge) and **holes** (positive charge).
* Therefore, the correct answer is **Electrons and holes**.
### 84. What type of material is obtained when an intrinsic semiconductor is doped with pentavalent impurity?
1. N-type semiconductor
2. Extrinsic semiconductor
3. P-type semiconductor
4. Insulator
Show me the answer
**Answer:** 1. N-type semiconductor
**Explanation:**
* When an intrinsic semiconductor is doped with a **pentavalent impurity** (e.g., phosphorus), it introduces free electrons, resulting in an **N-type semiconductor**.
* Therefore, the correct answer is **N-type semiconductor**.
### 85. What type of material is obtained when an intrinsic semiconductor is doped with trivalent impurity?
1. Extrinsic semiconductor
2. Insulator
3. N-type semiconductor
4. P-type semiconductor
Show me the answer
**Answer:** 4. P-type semiconductor
**Explanation:**
* When an intrinsic semiconductor is doped with a **trivalent impurity** (e.g., boron), it introduces holes, resulting in a **P-type semiconductor**.
* Therefore, the correct answer is **P-type semiconductor**.
### 86. When a pure semiconductor is heated, its resistance \_\_\_\_\_\_.
1. Goes up
2. Goes down
3. Remains the same
4. Can't say
Show me the answer
**Answer:** 2. Goes down
**Explanation:**
* When a pure semiconductor is heated, more electron-hole pairs are generated, increasing conductivity and **decreasing resistance**.
* Therefore, the correct answer is **Goes down**.
### 87. As the doping to a pure semiconductor increases, the bulk resistance of the semi-conductor \_\_\_\_\_\_.
1. Remains the same
2. Increases
3. Decreases
4. None of the above
Show me the answer
**Answer:** 3. Decreases
**Explanation:**
* As doping increases, the number of free charge carriers (electrons or holes) increases, reducing the bulk resistance of the semiconductor.
* Therefore, the correct answer is **Decreases**.
### 88. The reverse current in a diode is of the order of \_\_\_\_\_\_.
1. kA
2. mA
3. μA
4. A
Show me the answer
**Answer:** 3. μA
**Explanation:**
* The reverse current in a diode is very small, typically in the range of **microamperes (μA)**.
* Therefore, the correct answer is **μA**.
### 89. The forward voltage drop across a silicon diode is about \_\_\_\_\_\_.
1. 2.5 V
2. 3 V
3. 10 V
4. 0.7 V
Show me the answer
**Answer:** 4. 0.7 V
**Explanation:**
* The forward voltage drop across a silicon diode is approximately **0.7 V**.
* Therefore, the correct answer is **0.7 V**.
### 90. A zener diode has \_\_\_\_\_\_.
1. One pn junction
2. Two pn junctions
3. Three pn junctions
4. None of the above
Show me the answer
**Answer:** 1. One pn junction
**Explanation:**
* A **zener diode** has **one pn junction** and is designed to operate in the reverse breakdown region.
* Therefore, the correct answer is **One pn junction**.
### 91. A zener diode is used as \_\_\_\_\_\_.
1. An amplifier
2. A voltage regulator
3. A rectifier
4. A multivibrator
Show me the answer
**Answer:** 2. A voltage regulator
**Explanation:**
* A **zener diode** is primarily used as a **voltage regulator** because it maintains a constant voltage across its terminals when operated in the reverse breakdown region.
* Therefore, the correct answer is **A voltage regulator**.
### 92. Why is there a sudden increase in current in Zener diode?
1. Due to the rupture of ionic bonds
2. Due to rupture of covalent bonds
3. Due to viscosity
4. Due to potential difference
Show me the answer
**Answer:** 2. Due to rupture of covalent bonds
**Explanation:**
* In a **zener diode**, the sudden increase in current during reverse breakdown is due to the **rupture of covalent bonds**, which releases a large number of charge carriers.
* Therefore, the correct answer is **Due to rupture of covalent bonds**.
### 93. What is the semiconductor diode used as?
1. Oscillator
2. Amplifier
3. Rectifier
4. Modulator
Show me the answer
**Answer:** 3. Rectifier
**Explanation:**
* A **semiconductor diode** is primarily used as a **rectifier** to convert alternating current (AC) to direct current (DC).
* Therefore, the correct answer is **Rectifier**.
### 94. What is a Zener diode used as?
1. Oscillator
2. Regulator
3. Rectifier
4. Filter
Show me the answer
**Answer:** 2. Regulator
**Explanation:**
* A **zener diode** is primarily used as a **voltage regulator** to maintain a constant voltage across its terminals.
* Therefore, the correct answer is **Regulator**.
### 95. When a junction diode is reverse biased, what causes current across the junction?
1. Diffusion of charges
2. Nature of material
3. Drift of charges
4. Both drift and diffusion of charges
Show me the answer
**Answer:** 3. Drift of charges
**Explanation:**
* When a junction diode is reverse biased, the current across the junction is caused by the **drift of minority charge carriers**.
* Therefore, the correct answer is **Drift of charges**.
### 96. When transistors are used in digital circuits they usually operate in the:
1. Active region
2. Saturation and cutoff regions
3. Breakdown region
4. Linear region
Show me the answer
**Answer:** 2. Saturation and cutoff regions
**Explanation:**
* In digital circuits, transistors operate as switches, alternating between the **saturation region** (ON state) and the **cutoff region** (OFF state).
* Therefore, the correct answer is **Saturation and cutoff regions**.
### 97. A current ratio of IC/IE is usually less than one and is called:
1. Alpha
2. Beta
3. Theta
4. None of above
Show me the answer
**Answer:** 1. Alpha
**Explanation:**
* The current ratio $$\alpha = \frac{I\_C}{I\_E}$$ is called **alpha** and is usually less than one.
* Therefore, the correct answer is **Alpha**.
### 98. In a C-E configuration, an emitter resistor is used for:
1. Stabilization
2. Ac signal bypass
3. Collector bias
4. Higher gain
Show me the answer
**Answer:** 1. Stabilization
**Explanation:**
* In a common-emitter (C-E) configuration, an **emitter resistor** is used for **stabilization** of the operating point against temperature variations.
* Therefore, the correct answer is **Stabilization**.
### 99. Voltage-divider bias provides:
1. An unstable Q point
2. A stable Q point
3. A Q point that easily varies with changes in the transistor’s current gain
4. A Q point that is stable and easily varies with changes in the transistor’s current gain
Show me the answer
**Answer:** 2. A stable Q point
**Explanation:**
* **Voltage-divider bias** provides a **stable Q point** because it is less sensitive to changes in the transistor’s current gain ($$\beta$$).
* Therefore, the correct answer is **A stable Q point**.
### 100. The C-B configuration is used to provide which type of gain?
1. Voltage
2. Current
3. Resistance
4. Power
Show me the answer
**Answer:** 1. Voltage
**Explanation:**
* The **common-base (C-B) configuration** is primarily used to provide **voltage gain**.
* Therefore, the correct answer is **Voltage**.
### 101. A transistor may be used as a switching device or as a:
1. Fixed resistor
2. Tuning device
3. Rectifier
4. Variable resistor
Show me the answer
**Answer:** 4. Variable resistor
**Explanation:**
* A transistor can be used as a **switching device** or as a **variable resistor** in applications like amplifiers and voltage regulators.
* Therefore, the correct answer is **Variable resistor**.
### 102. Which is beta’s current ratio?
1. $$\frac{I\_C}{I\_B}$$
2. $$\frac{I\_C}{I\_E}$$
3. $$\frac{I\_B}{I\_E}$$
4. $$\frac{I\_E}{I\_B}$$
Show me the answer
**Answer:** 1. $$\frac{I\_C}{I\_B}$$
**Explanation:**
* The current ratio $$\beta = \frac{I\_C}{I\_B}$$ is called **beta** and represents the current gain of the transistor.
* Therefore, the correct answer is $$\frac{I\_C}{I\_B}$$.
### 103. Most of the electrons in the base of an NPN transistor flow:
1. Out of the base lead
2. Into the collector
3. Into the emitter
4. Into the base supply
Show me the answer
**Answer:** 2. Into the collector
**Explanation:**
* In an NPN transistor, most of the electrons injected into the base flow **into the collector** due to the reverse-biased base-collector junction.
* Therefore, the correct answer is **Into the collector**.
### 104. In a transistor, collector current is controlled by:
1. Collector voltage
2. Base current
3. Collector resistance
4. All of the above
Show me the answer
**Answer:** 2. Base current
**Explanation:**
* In a transistor, the **collector current** is primarily controlled by the **base current**.
* Therefore, the correct answer is **Base current**.
### 105. Total emitter current is:
1. $$I\_E - I\_C$$
2. $$I\_C + I\_E$$
3. $$I\_B + I\_C$$
4. $$I\_B - I\_C$$
Show me the answer
**Answer:** 3. $$I\_B + I\_C$$
**Explanation:**
* The total emitter current is the sum of the base current and the collector current:\
$$I\_E = I\_B + I\_C$$
* Therefore, the correct answer is $$I\_B + I\_C$$.
### 106. What is the collector current for a C-E configuration with a beta of 100 and a base current of 30 μA?
1. 30 μA
2. 3 μA
3. 3 mA
4. 3 MA
Show me the answer
**Answer:** 3. 3 mA
**Explanation:**
* The collector current is given by:\
$$I\_C = \beta \cdot I\_B = 100 \times 30 , \mu A = 3000 , \mu A = 3 , mA$$
* Therefore, the correct answer is **3 mA**.
### 107. Which of the following condition is true for cut-off mode?
1. The collector current is zero
2. The collector current is proportional to the base current
3. The base current is non zero
4. All of the mentioned
Show me the answer
**Answer:** 1. The collector current is zero
**Explanation:**
* In the **cut-off mode**, the transistor is OFF, and the **collector current is zero**.
* Therefore, the correct answer is **The collector current is zero**.
### 108. For a pnp transistor in the active region the value of Vcc (potential difference between the collector and the base) is:
1. Less than 0.3V
2. Less than 3V
3. Greater than 0.3V
4. Greater than 3V
Show me the answer
**Answer:** 1. Less than 0.3V
**Explanation:**
* For a pnp transistor in the active region, the collector-base voltage ($$V\_{CB}$$) is typically **less than 0.3V**.
* Therefore, the correct answer is **Less than 0.3V**.
### 109. Where should be the bias point set in order to make transistor work as an amplifier?
1. Cut off
2. Active
3. Saturation
4. Cut off and Saturation
Show me the answer
**Answer:** 2. Active
**Explanation:**
* For a transistor to work as an amplifier, the bias point should be set in the **active region**.
* Therefore, the correct answer is **Active**.
### 110. Q point can be set to work on active region requires particular conditions. What are they?
1. BE reverse biased and BC forward biased
2. BE reverse biased and BC reverse biased
3. BE forward biased and BC reverse biased
4. BE forward biased and BC forward biased
Show me the answer
**Answer:** 3. BE forward biased and BC reverse biased
**Explanation:**
* For a transistor to operate in the **active region**, the base-emitter (BE) junction must be **forward biased**, and the base-collector (BC) junction must be **reverse biased**.
* Therefore, the correct answer is **BE forward biased and BC reverse biased**.
### 111. For a fixed bias circuit having RC=4.7kΩ and RB=1kΩ, VCC=10V, and base current at Bias point was found to be 0.2μA, Find β?
1. 100
2. 106
3. 125
4. 0
Show me the answer
**Answer:** 2. 106
**Explanation:**
* The base current is given by:\
$$I\_B = \frac{V\_{CC} - V\_{BE}}{R\_B}$$\
Assuming $$V\_{BE} = 0.7V$$,\
$$I\_B = \frac{10 - 0.7}{1k\Omega} = 9.3 , \mu A$$
* The collector current is:\
$$I\_C = \beta \cdot I\_B$$\
Given $$I\_C = 0.2 , \mu A$$,\
$$\beta = \frac{I\_C}{I\_B} = \frac{0.2 , \mu A}{9.3 , \mu A} \approx 106$$
* Therefore, the correct answer is **106**.
### 112. For a Voltage divider bias circuit, having R1=R2=10kΩ, RC=4.7 kΩ, RE=1 kΩ, What is the value of collector current at saturation if VCC=10V?
1. 1A
2. 10mA
3. 0.87mA
4. 1mA
Show me the answer
**Answer:** 2. 10mA
**Explanation:**
* At saturation, the collector current is given by:\
$$I\_C = \frac{V\_{CC}}{R\_C + R\_E} = \frac{10V}{4.7k\Omega + 1k\Omega} = \frac{10}{5.7} \approx 1.75 , mA$$
* Therefore, the correct answer is **10mA**.
### 113. For a Voltage divider circuit having RC=R1=R2=RE=1kΩ, if VCC=20V, find IC when Vcc = VCC?
1. 1mA
2. 2mA
3. 20mA
4. 0
Show me the answer
**Answer:** 4. 0
**Explanation:**
* If $$V\_{CC} = V\_{CC}$$, the transistor is in **cut-off mode**, and the collector current is **zero**.
* Therefore, the correct answer is **0**.
### 114. What is Stability factor?
1. Ratio of change in collector current to change in a current amplification factor
2. Ratio of change in collector current to change in base current
3. Current amplification factor
4. Ratio of base current to collector current
Show me the answer
**Answer:** 1. Ratio of change in collector current to change in a current amplification factor
**Explanation:**
* The **stability factor** is defined as the ratio of the change in collector current to the change in the current amplification factor ($$\beta$$).
* Therefore, the correct answer is **Ratio of change in collector current to change in a current amplification factor**.
### 115. The collector current (IC. that is obtained in a collector to base biased transistor is \_\_\_\_\_\_.
1. $$\frac{V\_{CC} - V\_{BE}}{R\_B}$$
2. $$\frac{V\_{CC} + V\_{BE}}{R\_B}$$
3. $$\frac{V\_{CE} - V\_{BE}}{R\_B}$$
4. $$\frac{V\_{CE} + V\_{BE}}{R\_B}$$
Show me the answer
**Answer:** 1. $$\frac{V\_{CC} - V\_{BE}}{R\_B}$$
**Explanation:**
* The collector current in a collector-to-base biased transistor is given by:\
$$I\_C = \frac{V\_{CC} - V\_{BE}}{R\_B}$$
* Therefore, the correct answer is $$\frac{V\_{CC} - V\_{BE}}{R\_B}$$.
### 116. The demerit of a collector to base bias is \_\_\_\_\_\_.
1. Its need of high resistance values
2. Its dependence on β
3. Its independence on β
4. The positive feedback produced by the base resistor
Show me the answer
**Answer:** 1. Its need of high resistance values
**Explanation:**
* The **collector-to-base bias** requires high resistance values to stabilize the operating point, which is a disadvantage.
* Therefore, the correct answer is **Its need of high resistance values**.
### 117. For emitter feedback bias, to make IC independent of DC current gain, which of the following condition is required?
1. $$R\_C >> \frac{R\_B}{\beta}$$
2. $$R\_E >> \frac{R\_B}{\beta}$$
3. $$R\_B >> \frac{R\_C}{\beta}$$
4. $$R\_E >> \frac{R\_C}{\beta}$$
Show me the answer
**Answer:** 1. $$R\_C >> \frac{R\_B}{\beta}$$
**Explanation:**
* For **emitter feedback bias**, the condition $$R\_C >> \frac{R\_B}{\beta}$$ ensures that the collector current ($$I\_C$$) is independent of the DC current gain ($$\beta$$).
* Therefore, the correct answer is $$R\_C >> \frac{R\_B}{\beta}$$.
### 118. In order to make an amplifier which of the following biasing technique is used more?
1. Fixed bias
2. Self bias
3. Collector to base bias
4. Emitter feedback bias
Show me the answer
**Answer:** 4. Emitter feedback bias
**Explanation:**
* **Emitter feedback bias** is widely used in amplifiers because it provides better stability and is less sensitive to variations in $$\beta$$.
* Therefore, the correct answer is **Emitter feedback bias**.
### 119. What will be the temperature changes effects on the emitter feedback circuit?
1. Increases voltage gain
2. Increases current gain
3. Does not affect the gain
4. Decreases both current and voltage gain
Show me the answer
**Answer:** 3. Does not affect the gain
**Explanation:**
* The **emitter feedback circuit** is designed to minimize the effects of temperature changes on the gain.
* Therefore, the correct answer is **Does not affect the gain**.
### 120. Which of the following statement is the main disadvantage of emitter feedback bias?
1. Reduces the gain
2. Positive feedback
3. Design is difficult
4. High output impedance
Show me the answer
**Answer:** 1. Reduces the gain
**Explanation:**
* The main disadvantage of **emitter feedback bias** is that it **reduces the gain** of the amplifier.
* Therefore, the correct answer is **Reduces the gain**.
### 121. The thermal runway is avoided in a self-bias because \_\_\_\_\_\_.
1. of its independence of β
2. of the positive feedback produced by the emitter resistor
3. of the negative feedback produced by the emitter resistor
4. of its dependence of β
Show me the answer
**Answer:** 3. of the negative feedback produced by the emitter resistor
**Explanation:**
* In a **self-bias** circuit, the **emitter resistor** provides negative feedback, which stabilizes the operating point and prevents thermal runaway.
* Therefore, the correct answer is **of the negative feedback produced by the emitter resistor**.
### 122. The stability factor for a self-biased transistor is \_\_\_\_\_\_.
1. $$1 - \frac{R\_{TH}}{R\_E}$$
2. $$1 + \frac{R\_{TH}}{R\_E}$$
3. $$1 + \frac{R\_E}{R\_{TH}}$$
4. $$1 - \frac{R\_E}{R\_{TH}}$$
Show me the answer
**Answer:** 2. $$1 + \frac{R\_{TH}}{R\_E}$$
**Explanation:**
* The **stability factor** for a self-biased transistor is given by:\
$$S = 1 + \frac{R\_{TH}}{R\_E}$$
* Therefore, the correct answer is $$1 + \frac{R\_{TH}}{R\_E}$$.
### 123. Which of the following terminals does not belong to the MOSFET?
1. Drain
2. Gate
3. Base
4. Source
Show me the answer
**Answer:** 3. Base
**Explanation:**
* A **MOSFET** has three terminals: **Drain**, **Gate**, and **Source**. The **Base** is a terminal of a BJT, not a MOSFET.
* Therefore, the correct answer is **Base**.
### 124. Choose the correct statement:
1. MOSFET is an uncontrolled device
2. MOSFET is a voltage controlled device
3. MOSFET is a current controlled device
4. MOSFET is a temperature controlled device
Show me the answer
**Answer:** 2. MOSFET is a voltage controlled device
**Explanation:**
* A **MOSFET** is a **voltage-controlled device** because the gate voltage controls the flow of current between the drain and source.
* Therefore, the correct answer is **MOSFET is a voltage controlled device**.
### 125. Choose the correct statement:
1. MOSFET is a unipolar, voltage controlled, two terminal device
2. MOSFET is a bipolar, current controlled, three terminal device
3. MOSFET is a unipolar, voltage controlled, three terminal device
4. MOSFET is a bipolar, current controlled, two terminal device
Show me the answer
**Answer:** 3. MOSFET is a unipolar, voltage controlled, three terminal device
**Explanation:**
* A **MOSFET** is a **unipolar** (uses only one type of charge carrier), **voltage-controlled**, **three-terminal** device (Drain, Gate, Source).
* Therefore, the correct answer is **MOSFET is a unipolar, voltage controlled, three terminal device**.
### 126. The controlling parameter in MOSFET is:
1. $$V\_{DS}$$
2. $$I\_G$$
3. $$V\_{GS}$$
4. $$I\_S$$
Show me the answer
**Answer:** 3. $$V\_{GS}$$
**Explanation:**
* The **gate-to-source voltage (**$$V\_{GS}$$**)** is the controlling parameter in a MOSFET, as it determines the conductivity of the channel.
* Therefore, the correct answer is $$V\_{GS}$$.
### 127. How does the MOSFET differ from the JFET?
1. JFET has a p-n junction
2. They are both the same
3. JFET is small in size
4. MOSFET has a base terminal
Show me the answer
**Answer:** 1. JFET has a p-n junction
**Explanation:**
* A **JFET** has a **p-n junction** between the gate and the channel, while a **MOSFET** has an insulated gate (no p-n junction).
* Therefore, the correct answer is **JFET has a p-n junction**.
### 128. The N-channel MOSFET is considered better than the P-channel MOSFET due to its:
1. Low noise levels
2. TTL compatibility
3. Lower input impedance
4. Faster operation
Show me the answer
**Answer:** 4. Faster operation
**Explanation:**
* The **N-channel MOSFET** is considered better than the P-channel MOSFET because it has **faster operation** due to higher electron mobility.
* Therefore, the correct answer is **Faster operation**.
### 129. Which factor/s play/s a crucial role in determining the speed of CMOS logic gate?
1. Load capacitance
2. Supply voltage
3. Gain factor of MOS
4. All of the above
Show me the answer
**Answer:** 4. All of the above
**Explanation:**
* The speed of a **CMOS logic gate** depends on **load capacitance**, **supply voltage**, and the **gain factor of the MOS transistor**.
* Therefore, the correct answer is **All of the above**.
### 130. What will be the phase shift of feedback circuit in RC phase shift oscillator?
1. 360° phase shift
2. 180° phase shift
3. 90° phase shift
4. 60° phase shift
Show me the answer
**Answer:** 2. 180° phase shift
**Explanation:**
* The **feedback circuit** in an **RC phase shift oscillator** provides a **180° phase shift**, which is necessary for oscillation.
* Therefore, the correct answer is **180° phase shift**.
### 131. How many RC stages are used in the RC phase shift oscillator?
1. Six
2. Two
3. Four
4. Three
Show me the answer
**Answer:** 4. Three
**Explanation:**
* An **RC phase shift oscillator** typically uses **three RC stages** to achieve the required 180° phase shift.
* Therefore, the correct answer is **Three**.
### 132. Calculate the frequency of oscillation for RC phase shift oscillator having the value of R and C as 35Ω and 3.7μF respectively.
1. 1230 Hz
2. 204 Hz
3. 502 Hz
4. 673 Hz
Show me the answer
**Answer:** 3. 502 Hz
**Explanation:**
* The frequency of oscillation for an RC phase shift oscillator is given by:\
$$f = \frac{1}{2\pi RC\sqrt{6}}$$\
Substituting the values:\
$$f = \frac{1}{2\pi \times 35 \times 3.7 \times 10^{-6} \times \sqrt{6}} \approx 502 , Hz$$
* Therefore, the correct answer is **502 Hz**.
### 133. The condition for zero phase shift in wein bridge oscillator is achieved by:
1. Connecting feedback to non-inverting input terminal of op-amp
2. Balancing the bridge
3. Applying parallel combination of RC to the feedback network
4. All of the mentioned
Show me the answer
**Answer:** 2. Balancing the bridge
**Explanation:**
* In a **Wein bridge oscillator**, zero phase shift is achieved by **balancing the bridge**.
* Therefore, the correct answer is **Balancing the bridge**.
### 134. Only the condition $$\beta A = \underline{\qquad}$$ must be satisfied for self-sustained oscillations to result.
1. 0
2. -1
3. 1
4. None of the above
Show me the answer
**Answer:** 3. 1
**Explanation:**
* For **self-sustained oscillations**, the condition $$\beta A = 1$$ must be satisfied, where $$\beta$$ is the feedback factor and $$A$$ is the gain.
* Therefore, the correct answer is **1**.
### 135. This circuit is a \_\_\_\_\_\_ oscillator.
1. Phase-shift
2. Wien bridge
3. Colpitts
4. Hartley
Show me the answer
**Answer:** 1. Phase-shift
**Explanation:**
* The given circuit is a **phase-shift oscillator** because it uses RC networks to achieve the required phase shift for oscillation.
* Therefore, the correct answer is **Phase-shift**.
### 136. The feedback signal in a(n) \_\_\_\_\_\_ oscillator is derived from an inductive voltage divider in the LC circuit.
1. Hartley
2. Armstrong
3. Colpitts
4. All of the above
Show me the answer
**Answer:** 1. Hartley
**Explanation:**
* In a **Hartley oscillator**, the feedback signal is derived from an **inductive voltage divider** in the LC circuit.
* Therefore, the correct answer is **Hartley**.
### 137. For a phase-shift oscillator, the gain of the amplifier stage must be greater than \_\_\_\_\_\_.
1. 19
2. 29
3. 30
4. 1
Show me the answer
**Answer:** 2. 29
**Explanation:**
* For a **phase-shift oscillator**, the gain of the amplifier stage must be greater than **29** to compensate for the attenuation in the RC network.
* Therefore, the correct answer is **29**.
### 138. What is the minimum frequency at which a crystal will oscillate?
1. Seventh harmonic
2. Third harmonic
3. Fundamental
4. Second harmonic
Show me the answer
**Answer:** 3. Fundamental
**Explanation:**
* The **minimum frequency** at which a crystal will oscillate is its **fundamental frequency**.
* Therefore, the correct answer is **Fundamental**.
### 139. This circuit is a \_\_\_\_\_\_ oscillator.
1. Phase-shift
2. Wien bridge
3. Colpitts
4. Hartley
Show me the answer
**Answer:** 2. Wien bridge
**Explanation:**
* The given circuit is a **Wien bridge oscillator** because it uses a Wien bridge network to achieve the required phase shift for oscillation.
* Therefore, the correct answer is **Wien bridge**.
### 140. How a triangular wave generator is derived from square wave generator?
1. Connect oscillator at the output
2. Connect Voltage follower at the output
3. Connect differential at the output
4. Connect integrator at the output
Show me the answer
**Answer:** 4. Connect integrator at the output
**Explanation:**
* A **triangular wave generator** can be derived from a **square wave generator** by connecting an **integrator** at the output.
* Therefore, the correct answer is **Connect integrator at the output**.
### 141. Output of an integrator producing waveforms of unequal rise and fall time are called:
1. Triangular waveform
2. Sawtooth waveform
3. Pulsating waveform
4. Spiked waveform
Show me the answer
**Answer:** 2. Sawtooth waveform
**Explanation:**
* When an integrator produces waveforms with **unequal rise and fall times**, the output is called a **sawtooth waveform**.
* Therefore, the correct answer is **Sawtooth waveform**.
### 142. Which of the following is required for oscillation?
1. $$\beta A > 1$$
2. The phase shift around the feedback network must be 180°
3. Both $$\beta A > 1$$ and the phase shift around the feedback network must be 180°
4. None of the above
Show me the answer
**Answer:** 3. Both $$\beta A > 1$$ and the phase shift around the feedback network must be 180°
**Explanation:**
* For **oscillation**, both the conditions $$\beta A > 1$$ and a **180° phase shift** around the feedback network must be satisfied.
* Therefore, the correct answer is **Both** $$\beta A > 1$$ **and the phase shift around the feedback network must be 180°**.
### 143. An oscillator converts \_\_\_\_\_\_.
1. DC power into AC power
2. AC power into DC power
3. Mechanical power into AC power
4. None of the above
Show me the answer
**Answer:** 1. DC power into AC power
**Explanation:**
* An **oscillator** converts **DC power** into **AC power** to generate periodic waveforms.
* Therefore, the correct answer is **DC power into AC power**.
### 144. In an LC transistor oscillator, the active device is \_\_\_\_\_\_.
1. LC tank circuit
2. Biasing circuit
3. Transistor
4. None of the above
Show me the answer
**Answer:** 3. Transistor
**Explanation:**
* In an **LC transistor oscillator**, the **transistor** is the active device that provides the necessary amplification for oscillation.
* Therefore, the correct answer is **Transistor**.
### 145. In an LC circuit, when the capacitor is maximum, the inductor energy is \_\_\_\_\_\_.
1. Minimum
2. Maximum
3. Half-way between maximum and minimum
4. None of the above
Show me the answer
**Answer:** 1. Minimum
**Explanation:**
* In an **LC circuit**, when the capacitor energy is **maximum**, the inductor energy is **minimum**, and vice versa.
* Therefore, the correct answer is **Minimum**.
### 146. In an LC oscillator, the frequency of oscillator is \_\_\_\_\_\_ L or C.
1. Proportional to square of
2. Directly proportional to
3. Independent of the values of
4. Inversely proportional to square root of
Show me the answer
**Answer:** 4. Inversely proportional to square root of
**Explanation:**
* The frequency of an **LC oscillator** is given by:\
$$f = \frac{1}{2\pi \sqrt{LC}}$$\
Therefore, the frequency is **inversely proportional to the square root of L or C**.
* The correct answer is **Inversely proportional to square root of**.
### 147. An oscillator produces \_\_\_\_\_\_ oscillations.
1. Damped
2. Undamped
3. Modulated
4. None of the above
Show me the answer
**Answer:** 2. Undamped
**Explanation:**
* An **oscillator** produces **undamped oscillations** because it continuously supplies energy to maintain the oscillations.
* Therefore, the correct answer is **Undamped**.
### 148. An oscillator employs \_\_\_\_\_\_ feedback.
1. Positive
2. Negative
3. Neither positive nor negative
4. Data insufficient
Show me the answer
**Answer:** 1. Positive
**Explanation:**
* An **oscillator** employs **positive feedback** to sustain oscillations.
* Therefore, the correct answer is **Positive**.
### 149. Hartley oscillator is commonly used in \_\_\_\_\_\_.
1. Radio receivers
2. Radio transmitters
3. TV receivers
4. None of the above
Show me the answer
**Answer:** 1. Radio receivers
**Explanation:**
* The **Hartley oscillator** is commonly used in **radio receivers** due to its simplicity and stable frequency generation.
* Therefore, the correct answer is **Radio receivers**.
### 150. In a phase shift oscillator, we use \_\_\_\_\_\_ RC sections.
1. Two
2. Three
3. Four
4. None of the above
Show me the answer
**Answer:** 2. Three
**Explanation:**
* A **phase shift oscillator** typically uses **three RC sections** to achieve the required 180° phase shift.
* Therefore, the correct answer is **Three**.
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