IB Physics HL D.4.3 Motional emf Question Bank

Practise IB Physics HL D.4.3 by applying motional emf concepts to exam-style physics questions.

[Maximum number: 3]

A conducting rod of length L is moved with speed v at right angles to a uniform magnetic field of flux density B. The field is directed into the plane of the page.

Figure for Question D.4.3 (HL)—Motional emf question 1 — IB Physics HL

Show, using Faraday's law or otherwise, that the potential difference, V, established between the ends of the rod is V=v B L.

ALTERNATE 1

In time $\Delta t$ , rod moves a distance $v \Delta t$

Flux increases by $B(L v \Delta t)^{}$

«By Faraday» induced emf is the rate of change of flux: $\frac{B L v \Delta t}{\Delta t}$

«=BLv»

ALTERNATE 2

<<From $\varepsilon=-\frac{N \Delta \Phi}{\Delta t} \gg$

Recognition that $\Phi=B A$

Recognition that N = 1

Recognition that $\frac{\Delta A}{\Delta t}=L v \vee$

<<Leading to V=vBL OR $\varepsilon=\mathrm{BLv}>$

ALTERNATE 3

«In steady state» electrons stop drifting and so net force is zero q v B=q E

Substitution of $E=\frac{V}{L}$ to get result

ALT 1: Correct MP2 scores MP1

ALT2:

V and $\varepsilon$ are interchangeable. Ignore negative sign.

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D.4.3 (HL)—Motional emf question 1