Transformers & LC Oscillations — MH-CET Physics MCQs with Solutions
Free MH-CET Physics Transformers & LC Oscillations MCQs with step-by-step solutions (20 questions). Part of AC Circuits. Practise online on Prepizo — no login needed.
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Questions with solutions
Q1 — Transformers & LC Oscillations · easy · theory
A transformer works on the principle of:
A. Self induction
B. Mutual induction ✓ Correct
C. Eddy current damping
D. Electrostatic induction
Solution: The alternating flux produced by the primary links the secondary and induces an EMF in it.
Q2 — Transformers & LC Oscillations · easy · theory
For an ideal transformer, the ratio of secondary to primary voltage equals:
A. The ratio of secondary to primary current
B. The ratio of primary to secondary turns
C. The ratio of secondary to primary turns ✓ Correct
D. Unity always
Solution: $\dfrac{V_s}{V_p} = \dfrac{N_s}{N_p}$, since both windings link the same flux per turn.
Q3 — Transformers & LC Oscillations · medium · theory
For an ideal transformer with no losses:
A. $V_pV_s = I_pI_s$
B. $V_pI_s = V_sI_p$
C. $V_pI_p = V_sI_s$ ✓ Correct
D. $V_p = V_s$ always
Solution: Power in equals power out, so raising the voltage necessarily lowers the current in the same proportion.
Q4 — Transformers & LC Oscillations · easy · theory
In a step-up transformer:
A. The voltage is increased and the current is correspondingly decreased ✓ Correct
B. Both voltage and current are decreased
C. Both voltage and current are increased
D. The voltage is decreased and the current increased
Solution: Energy conservation forbids increasing both; a step-up transformer has more secondary turns than primary.
Q5 — Transformers & LC Oscillations · medium · theory
Which of the following is NOT a source of energy loss in a transformer?
A. The resistance of the load connected to the secondary ✓ Correct
B. Eddy current loss in the core
C. Copper loss in the windings
D. Hysteresis loss in the core
Solution: Energy delivered to the load is the useful output, not a loss; the other three are genuine internal losses.
Q6 — Transformers & LC Oscillations · medium · theory
A transformer cannot operate on a direct current supply because:
A. A steady current produces no change of flux, so no EMF is induced ✓ Correct
B. DC cannot flow through a copper winding
C. The turns ratio would become zero
D. DC would burn out the core immediately
Solution: Induction requires a changing flux, which only an alternating current can provide.
Q7 — Transformers & LC Oscillations · medium · theory
In an LC oscillator, the energy:
A. Remains entirely in the capacitor
B. Shuttles back and forth between the electric field of the capacitor and the magnetic field of the inductor ✓ Correct
C. Is steadily dissipated as heat in the capacitor
D. Is converted into mechanical energy
Solution: In an ideal lossless circuit the total energy stays constant while its form alternates twice each cycle.
Q8 — Transformers & LC Oscillations · medium · theory
The frequency of oscillation of an ideal LC circuit is:
A. $\dfrac{1}{\sqrt{LC}}$
B. $2\pi\sqrt{LC}$
C. $\dfrac{\sqrt{LC}}{2\pi}$
D. $\dfrac{1}{2\pi\sqrt{LC}}$ ✓ Correct
Solution: It is the same as the resonant frequency of a series LCR circuit, since the resistance does not enter.
Q9 — Transformers & LC Oscillations · medium · numerical
A transformer has $100$ primary turns and $500$ secondary turns. With $220\text{ V}$ applied to the primary, the secondary voltage is:
A. $1100\text{ V}$ ✓ Correct
B. $44\text{ V}$
C. $220\text{ V}$
D. $2200\text{ V}$
Solution: $V_s = V_p\dfrac{N_s}{N_p} = 220 \times \dfrac{500}{100} = 1100\text{ V}$.
Q10 — Transformers & LC Oscillations · easy · numerical
A transformer has a turns ratio of $1 : 10$. With $200\text{ V}$ on the primary, the secondary voltage is:
A. $200\text{ V}$
B. $2000\text{ V}$ ✓ Correct
C. $20\text{ V}$
D. $100\text{ V}$
Solution: $V_s = 200 \times 10 = 2000\text{ V}$ — a step-up transformer.
Q11 — Transformers & LC Oscillations · hard · numerical
An ideal transformer takes $5\text{ A}$ at $220\text{ V}$ and delivers $1100\text{ V}$. The secondary current is:
A. $1\text{ A}$ ✓ Correct
B. $25\text{ A}$
C. $5\text{ A}$
D. $0.2\text{ A}$
Solution: $I_s = \dfrac{V_pI_p}{V_s} = \dfrac{220 \times 5}{1100} = 1\text{ A}$.
Q12 — Transformers & LC Oscillations · medium · numerical
A step-down transformer has $1000$ primary and $100$ secondary turns. With $2200\text{ V}$ applied, the secondary voltage is:
A. $110\text{ V}$
B. $2200\text{ V}$
C. $220\text{ V}$ ✓ Correct
D. $22000\text{ V}$
Solution: $V_s = 2200 \times \dfrac{100}{1000} = 220\text{ V}$.
Q13 — Transformers & LC Oscillations · easy · numerical
A transformer takes $1000\text{ W}$ and delivers $900\text{ W}$. Its efficiency is:
A. $90\%$ ✓ Correct
B. $100\%$
C. $10\%$
D. $111\%$
Solution: Efficiency $= \dfrac{\text{output}}{\text{input}} \times 100 = \dfrac{900}{1000} \times 100 = 90\%$.
Q14 — Transformers & LC Oscillations · medium · numerical
An ideal transformer has a turns ratio $\dfrac{N_s}{N_p} = 20$. If the primary current is $10\text{ A}$, the secondary current is:
A. $2\text{ A}$
B. $10\text{ A}$
C. $0.5\text{ A}$ ✓ Correct
D. $200\text{ A}$
Solution: Current is inversely proportional to turns: $I_s = \dfrac{10}{20} = 0.5\text{ A}$.
Q15 — Transformers & LC Oscillations · hard · numerical
An LC circuit has $L = 1\text{ H}$ and $C = 1\,\mu\text{F}$. Its frequency of oscillation is approximately:
A. $318\text{ Hz}$
B. $50\text{ Hz}$
C. $1000\text{ Hz}$
D. $159\text{ Hz}$ ✓ Correct
Solution: $f = \dfrac{1}{2\pi\sqrt{LC}} = \dfrac{1}{2\pi \times 10^{-3}} \approx 159\text{ Hz}$.
Q16 — Transformers & LC Oscillations · hard · numerical
An LC circuit has $L = 2\text{ mH}$ and $C = 5\,\mu\text{F}$. Its frequency of oscillation is approximately:
A. $10^4\text{ Hz}$
B. $159\text{ Hz}$
C. $100\text{ Hz}$
D. $1592\text{ Hz}$ ✓ Correct
Solution: $f = \dfrac{1}{2\pi\sqrt{2 \times 10^{-3} \times 5 \times 10^{-6}}} = \dfrac{1}{2\pi \times 10^{-4}} \approx 1592\text{ Hz}$.
Q17 — Transformers & LC Oscillations · medium · numerical
A transformer steps $240\text{ V}$ down to $12\text{ V}$. Its turns ratio $N_p : N_s$ is:
A. $12 : 240$
B. $20 : 1$ ✓ Correct
C. $2 : 1$
D. $1 : 20$
Solution: $\dfrac{N_p}{N_s} = \dfrac{V_p}{V_s} = \dfrac{240}{12} = 20$.
Q18 — Transformers & LC Oscillations · medium · numerical
An ideal transformer delivers $1100\text{ V}$ at $1\text{ A}$. The power drawn from the primary is:
A. $1100\text{ W}$ ✓ Correct
B. $1000\text{ W}$
C. $5500\text{ W}$
D. $220\text{ W}$
Solution: An ideal transformer has no losses, so the input power equals the output power $1100 \times 1 = 1100\text{ W}$.
Q19 — Transformers & LC Oscillations · medium · numerical
If the capacitance of an LC oscillator is made four times as large, its frequency:
A. Doubles
B. Halves ✓ Correct
C. Remains unchanged
D. Becomes four times
Solution: $f \propto \dfrac{1}{\sqrt{C}}$, so quadrupling $C$ halves the frequency.
Q20 — Transformers & LC Oscillations · medium · numerical
A transformer has $200$ primary and $50$ secondary turns. With $240\text{ V}$ applied, the secondary voltage is:
A. $960\text{ V}$
B. $120\text{ V}$
C. $60\text{ V}$ ✓ Correct
D. $240\text{ V}$
Solution: $V_s = 240 \times \dfrac{50}{200} = 60\text{ V}$.