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IBDP Physics- D.4 Induction- IB Style Questions For HL Paper 1A -FA 2025

IBDP Physics HL Paper 1 -FA 2025- All Chapters

Question 

A conducting ring is perpendicular to a uniform magnetic field directed out of the page.

The magnitude of the magnetic field strength increases. What are the direction of the conventional current induced in the ring and the net magnetic force on the ring?

 Current induced in the ringMagnetic force on the ring
(A)clockwisezero
(B)counter-clockwisezero
(C)clockwisenon-zero
(D)counter-clockwisenon-zero
▶️ Answer/Explanation

Correct Answer: \( \boxed{\mathrm{A}} \)

The magnetic field is directed out of the page and its magnitude is increasing. By Lenz’s law, the induced current produces a magnetic field that opposes the increase in magnetic flux.

Therefore, the induced magnetic field must be directed into the page.

Using the right-hand grip rule, a magnetic field directed into the page is produced by a clockwise conventional current.

Thus, the induced current is clockwise.

For a uniform magnetic field, the magnetic forces acting on opposite elements of the circular ring are equal in magnitude and opposite in direction. Their vector sum is therefore zero.

Hence, the net magnetic force on the ring is zero.

Therefore,

\( \boxed{\text{clockwise current, zero net force}} \)

Hence, the correct answer is \( \boxed{\mathrm{A}} \).

Question 

The graph shows how the magnetic flux linked through a conducting coil varies with time. The coil has only one turn.

F

What is the maximum emf induced in the coil?

(A) \(0.40\,\mathrm{V}\)
(B) \(1.0\,\mathrm{V}\)
(C) \(2.0\,\mathrm{V}\)
(D) \(4.0\,\mathrm{V}\)
▶️ Answer/Explanation

Correct Answer: \( \boxed{\mathrm{C}} \)

Faraday’s law of electromagnetic induction gives

\(\mathcal{E}=-N\frac{\Delta\Phi}{\Delta t}\)

The magnitude of the induced emf is therefore equal to the magnitude of the gradient of the magnetic flux-time graph.

From \(t=0\) to \(t=4\,\mathrm{s}\), the flux changes from \(0\) to \(4\,\mathrm{Wb}\), giving

\(\left|\mathcal{E}\right|=\frac{4}{4}=1.0\,\mathrm{V}\)

From \(t=4\,\mathrm{s}\) to \(t=8\,\mathrm{s}\), the flux is constant, so the induced emf is zero.

From \(t=8\,\mathrm{s}\) to \(t=10\,\mathrm{s}\), the flux decreases from \(4\,\mathrm{Wb}\) to \(0\,\mathrm{Wb}\). Therefore,

\(\left|\mathcal{E}\right|=\frac{4}{2}=2.0\,\mathrm{V}\)

The maximum induced emf is therefore

\( \boxed{\mathcal{E}_{\mathrm{max}}=2.0\,\mathrm{V}} \)

Hence, the correct answer is \( \boxed{\mathrm{C}} \).

Question

Which law is equivalent to the law of conservation of energy?
A. Coulomb’s law
B. Ohm’s law
C. Newton’s first law
D. Lenz’s law
▶️ Answer/Explanation
Detailed solution

Lenz’s law states that the direction of an induced emf and the resulting current is such that it opposes the change in magnetic flux that produces it.

This opposition ensures that energy is not created from nothing. Any induced current requires work to be done by an external agent, and this work is converted into electrical energy.

If the induced current were to assist the change in flux rather than oppose it, energy would be produced without any external work, violating the law of conservation of energy.

Therefore, Lenz’s law is a direct consequence of the law of conservation of energy.

✅ Answer: (D)

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