# Objective Questions on Electronics | MCQ on Electronics 13

1. An emitter follower has a voltage gain that is

The voltage gain is nothing but the ratio of the output voltage of an amplifier to its input voltage in open circuit condition. An emitter follower has the output voltage that is nearly equal to the input voltage. Hence, the voltage is gain is almost exactly unity.

2. The input impedance of the base of an emitter follower is usually

The input impedance of the emitter follower is given as,
RIN = (β + 1) * [(VBE / IC) + RL]
Since, we know that the β is current gain of the emitter follower and the current gain is very high in the emitter follower circuit. Hence, here the current gain and input impedance are directly proportional to each other. So, the input impedance of an emitter follower is very high.

3. The ac base voltage of an emitter follower is across the

The ac base voltage of an emitter follower is approximately equal to the input voltage in between the base and emitter. But in an emitter follower the input voltage is connected to the series combination of base-emitter terminal and the external emitter resistance. The base-emitter junction acts as a diode and this is called as emitter diode. Hence, we know that the total AC base voltage is the summation of the voltage drop across the emitter diode and the external AC emitter resistance.

4. The output voltage of an emitter follower is across the

In an emitter follower, the load resistance is connected in the output side. So, there is a voltage drop across the load resistance. This voltage drop is nothing but the output voltage of an emitter follower. Hence, it is measured across the load resistance.

5. The input voltage to an emitter follower is usually

Due to the source resistance of the emitter follower there is a small voltage drop across the source resistance. So, rest of the remaining voltage only goes to the input side of emitter follower and hence the input voltage is always less than the generator voltage.

6. In 8085 name the 16 bit registers?

Program Counter (PC) and Stack Pointer (SP) are basically used to hold 16-bit memory addresses. PC stores the 16-bit memory address of the next instruction to be fetched. SP can be used to temporarily store the 16-bit memory address as well as data. So PC & SP are 16-bit registers.

7. What is SIM?

SIM stands for “Set Interrupt Mask” which is handling the interrupts in 8085 microprocessor.

8. Piezoelectric effect is utilized in which of the following filter?

A crystal filter refers to a filter produced by using a quartz crystal unit having a stable frequency and steep resonance characteristics relative to the temperature change. Here, the quartz crystal oscillator is worked on the principle of piezoelectric effect. Hence, this piezoelectric effect is utilized in the crystal oscillator.

9. Frequency of the given waveform is

Since it is a periodic but non alternating waveform hence here the time period is T = 100 msec. f = 1/T = 1/ 100 X 10-3 = 10Hz.

10. In an inductor current cannot change abruptly. Comment on the statement.

Yes, in an inductor, current cannot change abruptly, because the current is opposed by the creation of magnetic field when current flowing in it.

11. A 100 ohm resistor is directly connected across a 80 V battery. What is the power dissipation?

I = V / R = 80 / 100 = 0.8 A.
So power = I2R = 64 W.

12. The set of which logic gates is designated as universal gate?

They are called universal gates because we can be constructed the other gates by using any one of those two gates.

13. The main advantage of Anderson’s bridge over Maxwell bridge is that

In the Anderson’s Bridge, there is no need of standard variable capacitor to obtain the unknown value of inductor. We can use normal fixed value capacitor in this bridge. But, we are using the standard variable capacitor in Maxwell Bridge. So, the cost of the standard variable capacitor is higher than the normal fixed value capacitor. Hence, the circuit construction cost of Anderson’s Bridge is less than the Maxwell Bridge.

14. The effective reactance of an inductive coil

When the frequency of the supply increases in the inductor, the capacitance is formed in between the air-gap of two conductors of that inductor. This capacitance formation is not useful for us. So, it is called as stray capacitance. This stray capacitance produces the opposite reaction to the inductor. Hence, the effective reactance reduces because of this reason.

15. The measurement of a quantity

For example, we used to measure the one meter length by one meter scale. Here, one meter scale is accurately known predefined acceptable standard. But, the one meter length is unknown quantity. Here, we are comparing this unknown quantity (one meter length) with the accurately known predefined acceptable standard (one meter scale) and finally we are concluding that the measurement is finished by this process. This is the perfect example of the term “measurement”.

16. The internal resistance of Weston standard cell is of order of

The internal resistance of an unsaturated western standard cell is typically very less. It is normally less than 1 ohm.

17. The internal resistance of a saturated Weston Cell is of order of a

The internal resistance of a saturated western standard cell is typically high. It is normally between 100 ohms to 850 ohms.

18. Which of the following meter is most suitable for measuring radio frequency currents?

In a thermocouple meter, when the current flows through the heating element, the voltage is developed across the open ends of the thermo couple. When the radio frequency current flows through the heating element, it generates more voltage across the open ends. This output voltage is measured by moving coil DC meter. This output voltage is directly proportional to the heat generation in that element. Hence, the thermocouple meter is most suitable for measuring the radio frequency current.

19. A single phase full bridge inverter can operate in load commutation mode in case load consists of

In a load commutation mode single phase full bridge inverter, if the load is not connected to the inverter, the SCRs would never be tuned off and after half cycle a short circuit would develop through SCR1 and SCR4. If it is not possible to guarantee that a load will always provide the proper counter voltage for commutation. This counter voltage can be provided by the RLC under damped loads for achieving the proper commutation.

20. Schering bridge is used to measure which of the following?

Wien Bridge is used to measure the frequency. Maxwell Bridge and Anderson Bridge are used to find the inductance. Schering Bridge is used to measure the capacitance and Whetstone Bridge and Kelvin Bridge are used to find the resistance.

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