
- AThe rms current in circuit (b) can be larger than that in (a)
- BThe rms current in figure (a) is always equal to that in figure (b)
- CThe rms current in circuit (b) can never be larger than that in (a)
- DAt resonance, current in (b) is less than that in (a)
View written solutionFree
Correct answer: C
Let the two figures be the standard AC circuits:
- (a): a series circuit connected to an AC source
- (b): a parallel circuit connected to an AC source
We compare their rms currents drawn from the source.
1. Current in series circuit (a)
For a series circuit, the impedance is
Hence the rms current is
Since
we get
with equality at resonance:
So at resonance,
which is maximum for the series circuit.
2. Current in parallel circuit (b)
For a parallel circuit, source current is found from admittance:
Thus rms current drawn from source is
Since
we get
with equality at resonance.
At resonance,
so
which is minimum for the parallel circuit.
3. Comparison of and
From above,
Therefore,
for all frequencies, and equality holds only at resonance.
So:
- circuit (b) can be larger than circuit (a) away from resonance
- they are not always equal
- circuit (b) can never be larger is false
- at resonance, they are equal, not less
4. Check each option
Option A
The rms current in circuit (b) can be larger than that in (a)
This is true because away from resonance,
Option B
The rms current in figure (a) is always equal to that in figure (b)
This is false. They are equal only at resonance.
Option C
The rms current in circuit (b) can never be larger than that in (a)
This is false.
Option D
At resonance, current in (b) is less than that in (a)
This is false because at resonance,
5. Final answer
The correct option is:
6. Comparison with stored answer
Stored correct answer:
Our derived answer is , so the stored answer does not match the physics of standard series and parallel circuits. In fact, the comparison shows:
not the reverse.
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