# Power Electronics Questions and Answers – Filters-2

This set of Power Electronics Multiple Choice Questions & Answers (MCQs) focuses on “Filters-2”.

1. A diode rectifier with a C filter will have average output voltage _______ than that obtained by a rectifier without the C filter.
a) lower than
b) higher than
c) same as
d) none of the mentioned

Explanation: C filter improves the efficiency and eliminates ripples by keeping the output voltage constant.

2. An inductor filter connected in series with a resistive load provides a
a) smoothing of the output voltage waveform
b) smoothing of the input voltage waveform
c) smoothing of the output current waveform
d) smoothing of the input current waveform

Explanation: Filter is always connected to the load side (output). Inductor has the property of keeping the current smooth and constant.

3. In the below given configuration, L is connected as a filter across the R load. The average ammeter current is
a) 2Vm/R
b) 2Vm/πR
c) Vm/πR
d) Vm/R

Explanation: I = Vo/R
Vo = 2Vm/π.

4. The current ripple factor (CRF) is the ratio of
a) Average value/RMS value
b) RMS value/Average value
c) Average value/Maximum value
d) Maximum value/RMS value

Explanation: CRF = Ir/Io.

5. In case of an L filter, the ripple current increases with
c) increase in the value of L
d) ripple current never increases

Explanation: When the load is reduced the resistance R is increased & ripple current increases.
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6. In case of a C filter, if R (load resistance) is increased
a) ripple factor is reduced
b) ripple factor is increased
c) ripple factor is not affected
d) increases noise in the circuit

Explanation: The time constant RC is increased therefore the ripple factor is reduced.

7. When a certain type of filter is connected across the R load, of a full wave bridge diode biased rectifier the following output current waveform is obtained. The filter connected is most likely a
a) L filter
b) C filter
c) LC filter
d) None of the above mentioned

Explanation: The above waveform is that of the output current. The peak per half cycle is on the right, hence it is more likely to be an L filter.

8. C filters are suitable for ___________ load resistances and L filters are suitable for _____________ load resistances.
a) low, low
b) high, high
c) high, low
d) low, high

Explanation: In case of L filter, if R is lowered, the time constant (L/R) increases, therefore ripple factor reduces. In case of a C filter, the time constant RC is increased, therefore, ripple factor is reduced.

9. An LC filter will have ripple factor value___________ (For the same value of L & C)
a) lower than that obtained by L filter but higher than that obtained by C filter
b) lower than that obtained by C filter but higher than that obtained by L filter
c) lower than that obtained by either L or C filter
d) higher than that obtained by either L or C filter

Explanation: Simply, an LC filter combines both the advantages of L and C filters.

10. In a single-phase full wave rectifier ___________ order harmonics are the most dominant
a) first
b) second
c) third
d) fourth

Explanation: The output voltage is given by,
Vo = (2Vm/π) – (4Vm/3π)cos 2ωt – (4Vm/15π)cos 4ωt . . . .
Hence the other values after the second factor (4Vm/3π) become very very small hence they can be eliminated.

Sanfoundry Global Education & Learning Series – Power Electronics.

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