Electromagnetic induction IB DP Physics Study Notes - 2025 Syllabus

Electromagnetic induction IB DP Physics Study Notes

Electromagnetic induction IB DP Physics Study Notes at IITian Academy focus on specific topic and type of questions asked in actual exam. Study Notes focus on IB Physics syllabus with Students should understand

magnetic flux Φ as given by Φ = BA cos θ
that a time-changing magnetic flux induces an emf ε as given by Faraday’s law of induction ε = -N ΔΦ/Δt
that a uniform magnetic field induces an emf in a straight conductor moving perpendicularly to it as given by ε = BvL
that the direction of induced emf is determined by Lenz’s law and is a consequence of energy conservation

Standard level and higher level: There is no standard level content.
Additional higher level: 6 hours

IB DP Physics 2025 -Study Notes -All Topics

Electromotive Force (emf)

Consider the magnetic field (B-field) provided by a horseshoe magnet (a curved bar magnet).
If we place a stationary charge $ q $ within the B-field, it will feel no magnetic force.
Yet if we project the charge $ q $ through the B-field with a velocity $ v $, it will feel a force:

Example:

What is the magnetic force on a charge of $ 2.0 \times 10^{-6} \, \text{C} $ moving at $ 4.0 \times 10^3 \, \text{m/s} $ perpendicular to a magnetic field of strength $ 0.25 \, \text{T} $?

▶️ Answer/Explanation

Using $ F = qvB $, since $ \sin 90^\circ = 1 $:

$ F = (2.0 \times 10^{-6})(4.0 \times 10^3)(0.25) = \boxed{2.0 \times 10^{-3} \, \text{N}} $

Induced Electromotive Force (emf)

If the north pole of a magnet is suddenly thrust through a looped conductor, a current is created.
Current travels through the circuit only while the magnet is moving through the loop. ✅
Current direction depends on which direction the magnet is being moved. ✅

Relative motion between a conductor and a B-field induces emf. This is the principle behind electricity generation using turbines.

Example:

Show that the emf $ \varepsilon $ induced in a straight conductor of length $ \ell $ moving at velocity $ v $ through a magnetic field of strength $ B $ is $ \varepsilon = Bv\ell $.

▶️ Answer/Explanation

We know $ F = qvB $, and $ F = qE = \frac{qV}{\ell} $. Equating:

$ \frac{qV}{\ell} = qvB \Rightarrow V = Bv\ell = \boxed{\varepsilon} $

Magnetic Flux

When a loop lies in the same plane as the B-field, few field lines pass through → No current induced.
Magnetic flux $ \Phi = BA \cos \theta $

Example:

A magnetic field of strength $ 0.20 \, \text{T} $ passes through a loop of area $ 0.05 \, \text{m}^2 $ at an angle of $ 60^\circ $. Find the magnetic flux.

▶️ Answer/Explanation

$ \Phi = B A \cos \theta = 0.20 \times 0.05 \times \cos 60^\circ = \boxed{5.0 \times 10^{-3} \, \text{Wb}} $

Magnetic Flux Density

Magnetic flux density: $ B = \frac{\Phi}{A \cos \theta} $
Magnetic flux is measured in webers (Wb), $ 1 \, \text{Wb} = 1 \, \text{T·m}^2 $

Example:

A coil has an area $ A = 0.1 \, \text{m}^2 $ and lies in a magnetic flux of $ \Phi = 3 \times 10^{-3} \, \text{Wb} $ at $ \theta = 0^\circ $. Find the flux density $ B $.

▶️ Answer/Explanation

$ B = \frac{\Phi}{A \cos \theta} = \frac{3 \times 10^{-3}}{0.1 \times 1} = \boxed{0.03 \, \text{T}} $

Magnetic Flux Linkage

Flux linkage $ N\Phi = NBA\cos\theta $
Induced emf occurs only when flux changes.

Example:

A coil with $ N = 200 $ turns has an area of $ 0.02 \, \text{m}^2 $ and lies in a $ 0.3 \, \text{T} $ field at angle $ 0^\circ $. Find the flux linkage.

▶️ Answer/Explanation

$ \Phi = B A \cos\theta = 0.3 \times 0.02 \times 1 = 6.0 \times 10^{-3} \, \text{Wb} $

$ N\Phi = 200 \times 6.0 \times 10^{-3} = \boxed{1.2 \, \text{Wb-turns}} $

Faraday’s Law & Lenz’s Law

Faraday’s law: $ \varepsilon = -\frac{d(N\Phi)}{dt} $
Lenz’s law: The direction of induced emf opposes the change in flux.

Example:

Flux through a coil of 50 turns changes from 0.10 Wb to 0 in 0.20 s. Find the average emf induced.

▶️ Answer/Explanation

$ \varepsilon = -\frac{\Delta(N\Phi)}{\Delta t} = -\frac{50 \times (0 – 0.10)}{0.20} = \boxed{25 \, \text{V}} $

Question

A coil X is connected to a cell and a switch that is initially open. Coil Y has its plane parallel to X. X and Y have a common axis.

When the switch is closed a force F acts on Y due to X. What is the variation with time of F and what is the direction of F?

▶️Answer/Explanation

Ans D

Question

The coil of a direct current electric motor is turning with a period $T$. At $t=0$ the coil is in the position shown in the diagram. Assume the magnetic field is uniform across the coil.

Which graph shows the variation with time of the force exerted on section $\mathrm{XY}$ of the coil during one complete turn?

▶️Answer/Explanation

Ans:A

Electromagnetic induction IB DP Physics Study Notes

Electromagnetic induction IB DP Physics Study Notes - 2025 Syllabus