# Electronic Devices and Circuits Questions and Answers – Capacitor Filters

This set of Electronic Devices and Circuits Multiple Choice Questions & Answers (MCQs) focuses on “Capacitor Filters”.

1. In a shunt capacitor filter, the mechanism that helps the removal of ripples is_________
a) The current passing through the capacitor
b) The property of capacitor to store electrical energy
c) The voltage variations produced by shunting the capacitor
d) Uniform charge flow through the rectifier

Explanation: Filtering is frequently done by shunting the load with capacitor. It depends on the fact that a capacitor stores energy when conducting and delivers energy during non conduction. Throughout this process, the ripples are eliminated.

2. The cut-in point of a capacitor filter is_________
a) The instant at which the conduction starts
b) The instant at which the conduction stops
c) The time after which the output is not filtered
d) The time during which the output is perfectly filtered

Explanation: The capacitor charges when the diode is in ON state and discharges during the OFF state of the diode. The instant at which the conduction starts is called cut-in point. The instant at which the conduction stops is called cut-out point.

3. The rectifier current is a short duration pulses which cause the diode to act as a_________
a) Voltage regulator
b) Mixer
c) Switch
d) Oscillator

Explanation: The diode permits charge to flow in capacitor when the transformer voltage exceeds the capacitor voltage. It disconnects the power source when the transformer voltage falls below that of a capacitor.

4. A half wave rectifier, operated from a 50Hz supply uses a 1000µF capacitance connected in parallel to the load of rectifier. What will be the minimum value of load resistance that can be connected across the capacitor if the ripple% not exceeds 5?
a) 114.87Ω
b) 167.98Ω
c) 115.47Ω
d) 451.35Ω

Explanation: For a half wave filter,
ϒ=1/2√3 fCRL=1/2√3*50*10-3*RL
RL=103/5√3=115.47Ω.

5. A 100µF capacitor when used as a filter has 15V ac across it with a load resistor of 2.5KΩ. If the filter is the full wave and supply frequency is 50Hz, what is the percentage of ripple frequency in the output?
a) 2.456%
b) 1.154%
c) 3.785%
d) 3.675%

Explanation: For a full wave rectifier, ϒ=1/4√3 fCRL
=1/4√3*50*10-3*2.5
=0.01154. So, ripple is 1.154%.
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6. A full wave rectifier uses a capacitor filter with 500µF capacitor and provides a load current of 200mA at 8% ripple. Calculate the dc voltage.
a) 15.56V
b) 20.43V
c) 11.98V
d) 14.43V

Explanation: The ripple factor ϒ=IL/ 4√3 fCVDC
VDC=200*10-3/ 4√3 *50*500*8
=14.43.

7. The charge (q) lost by the capacitor during the discharge time for shunt capacitor filter.
a) IDC*T
b) IDC/T
c) IDC*2T
d) IDC/2T

Explanation: The ‘T’ is the total non conducting time of capacitor. The charge per unit time will give the current flow.

8. Which of the following are true about capacitor filter?
a) It is also called as capacitor output filter
b) It is electrolytic
c) It is connected in parallel to load
d) It helps in storing the magnetic energy

Explanation: The rectifier may be full wave or half wave. The capacitors are usually electrolytic even though they are large in size.

9. The rms ripple voltage (Vrms) of a shunt filter is_________
a) IDC/2√3
b) IDC2√3
c) IDC/√3
d) IDC√3

Explanation: The ripple waveform will be triangular in nature. The rms value of this wave is independent of slopes or lengths of straight lines. It depends only on the peak value.

10. A shunt capacitor of value 500µF fed rectifier circuit. The dc voltage is 14.43V. The dc current flowing is 200mA. It is operating at a frequency of 50Hz. What will be the value of peak rectified voltage?
a) 18.67V
b) 16.43V
c) 15.98V
d) 11.43V

Explanation: We know, Vm=Vdc+Idc/4fC
=14.43+ {200/ (200*500)} 103
=14.43+2=16.43V.

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