# Electronic Devices and Circuits Questions and Answers – L-Section Filter

This set of Electronic Devices and Circuits Multiple Choice Questions & Answers (MCQs) focuses on “L-Section Filter”.

1. An L section filter with L=2henry and C= 49µF is used in the output of a full wave single phase rectifier that is fed from a 40-0-40 V peak transformer. The load current is 0.2A. Calculate the output dc voltage.
a) 20.76V
b) 24.46V
c) 34.78V
d) 12.67V

Explanation: Given, VL= 40V.
VDC=2/π*VL=2/π*40=25.46V.

2. Calculate LC for a full wave rectifier which provides 10V dc at 100mA with a maximum ripple of 2%. Input ac frequency is 50Hz.
a) 40*10-6
b) 10*10-6
c) 30*10-6
d) 90*10-6

Explanation: LC=1/6√2ω2ϒ
ω=2πf=314
By putting the values, LC=1/6√2(314)2 0.02=40*10-6.

3. The value of inductance at which the current in a choke filter does not fall to zero is_________
a) peak inductance
b) cut-in inductance
c) critical inductance
d) damping inductance

Explanation: When the value of inductance is increased, a value is reached where the diodes supplies current continuously. This value of inductance is called critical inductance.

4. The condition for the regulation curve in a choke filter is_________
a) LC≥RL/3ω
b) LC≤RL/3ω
c) L≥RL/3ω
d) LC≥RL

Explanation: IDC should not exceed the negative peak of ac component. So, the regulation curve in direct output voltage against load current for a filter is given the relation LC≥RL/3ω.

5. The ripple factor for an l section filter is_______
a) ϒ= 1/6√2ω2LC
b) ϒ= 6√2ω2LC
c) ϒ= 6√3ω2LC
d) ϒ= 1/6√3ω2LC

Explanation: The ripple factor is the ratio of root mean square (rms) value of ripple voltage to absolute value of dc component. It can also be expressed as the peak to peak value.

6. The output dc voltage of an LC filter is_______
a) VDC=2Vm/π + IDCR
b) VDC=Vm/π – IDCR
c) VDC=2Vm/π – 2IDCR
d) VDC=2Vm/π – IDCR

Explanation: The value for VDC is same as that of inductor filter. If inductor has no dc resistance, then VDC=2Vm/π. If R is the series resistance of transformer, then VDC=2Vm/π – IDCR.

7. The rms value of ripple current for an L section filter is_______
a) IRMS=√2/3*XL*VDC
b) IRMS=√2/3*XL*VDC
c) IRMS=√2/3*XL *VDC
d) IRMS=√2/3*XL*VDC

Explanation: The ac current through L is determined primarily by XL=2ωL. It is directly proportional to voltage produced and indirectly proportional to the reactance.

8. What makes the load in a choke filter to bypass harmonic components?
a) capacitor
b) inductor
c) resistor
d) diodes

Explanation: When the capacitor is shunted across the load, it bypasses the harmonic components. This is because it offers low reactance to ac ripple component. In another hand the inductor offers high impedance to harmonic terms.

9. The ripple to heavy loads by a capacitor is_______
a) high
b) depends on temperature
c) low
d) no ripple at all

Explanation: Ripple factor is inversely proportional to load resistance for a capacitor filter.
So, the ripples that are produced are low when the load is high.

10. In a choke l section filter_______
a) the inductor and capacitor are connected across the load
b) the inductor is connected in series and capacitor is connected across the load
c) the inductor is connected across and capacitor is connected in series to the load
d) the inductor and capacitor are connected in series

Explanation: The choke filter is sometimes also called as L section filter because the inductor and capacitor are connected in the shape ’L’ or inverted manner. But several sections of this choke filter are employed to smooth the output curve and make it free from ripples.

Sanfoundry Global Education & Learning Series – Electronic Devices and Circuits.

To practice all areas of Electronic Devices and Circuits, here is complete set of 1000+ Multiple Choice Questions and Answers.

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