This set of Analog Circuits Multiple Choice Questions & Answers (MCQs) focuses on “Resistance Level”.

1. What is quiescent point or Q-point?

a) Operating point of device

b) The point at which device have maximum functionality

c) The point at which current equal to voltage

d) The point of V-I graph where slope is 0.5

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Explanation: Quiescent point of a device represents operating point of a device. For a diode quiescent point is determined by constant DC current through the diode. The Q-point is the DC voltage or current at a specified terminal of an active device with no input applied. A bias circuit is used to supply this steady voltage/current.

2. The reciprocal of slope of current-voltage curve at Q-point gives _____________

a) AC resistance

b) Nominal resistance

c) Maximum dynamic resistance

d) Minimum impedance

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Explanation: Reciprocal of slope of I-V graph at q-point gives AC or dynamic resistance. The inverse of slope will be change in voltage by change in current which is known as dynamic resistance.

3. As the slope of I-V graph at the Q point increases, AC resistance will _____________

a) Increase

b) Decrease

c) Either increase or decrease

d) Neither increase nor decrease

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Explanation: Slope of I-V graph at q-point is reciprocal of dynamic or AC resistance. Therefore, as slope increases resistance decreases.

4. Static resistance of a diode is ____________

a) Resistance at the q-point, ΔV_{D}/ΔI_{D}

b) Maximum AC resistance

c) Minimum AC resistance

d) Resistance at operating point, V_{D}/I_{D}

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Explanation: Static or DC resistance of a diode is the resistance offered by a diode at its q-point. DC resistance represents steady state. That is, it is calculated by treating current and voltage as constants.

5. Average AC resistance and dynamic resistance are ____________

a) Always Equal

b) Never equal

c) Both represents same quantity

d) Calculated from V-I graph

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Explanation: Average AC resistance and dynamic or AC resistance are not exactly the same. They both measure the resistance in different ways. AC resistance is slope of the tangent of the curve of characteristic graph at Q-point. But average AC resistance is measured by measuring the slope of straight line between the limits of operation.

6. After cut-in voltage AC resistance of diode ____________

a) Slightly decreases

b) Decreases exponentially

c) Slightly increases

d) Increases exponentially

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Explanation: After cut-in voltage current exponentially increases with small increase in voltage. This will considerably reduce resistance.

7. DC resistance of diode is measured at ____________

a) Knee current

b) Cut-in voltage

c) Q-point

d) Reverse breakdown point

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Explanation: Static or DC resistance of a diode is the resistance offered by a diode at its q-point. DC resistance represents steady state. That is, it is calculated by treating current and voltage as constants.

8. Determine DC resistance of a diode described by characteristic graph at I_{D} = 10mA.

a) 90 Ω

b) 111.1 Ω

c) 101.0 Ω

d) 100 Ω

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Explanation: Static or DC resistance is the resistance of a diode at its operating point.

That is DC resistance = 0.9/10mA = 0.9×1000/10 = 90Ω.

9. For a diode, at 10mA DC resistance is 70Ω. The voltage corresponding to 10mA will be ____________

a) 0.5V

b) 0.6V

c) 0.7V

d) 0.8V

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Explanation: Static or DC resistance is the resistance of a diode at its operating point.

Resistance = voltage/current

Therefore, voltage = current x resistance = 10mA x70 =0.7V

10. Calculate the DC resistance of diode at VD= -10V from the characteristic graph given below.

a) 1MΩ

b) 10MΩ

c) 15MΩ

d) 5MΩ

View Answer

Explanation: Static or DC resistance is the resistance of a diode at its operating point.

Static resistance at -10V = 10V/current at -10V =10/1µA =10MΩ.

**Sanfoundry Global Education & Learning Series – Analog Circuits.**

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