IB Physics SL D 3 2 Charge in Magnetic Fields Questions

Calculate magnetic forces on moving charges and use circular-motion relationships to analyse particle paths, radii, frequencies and mass separation.

Exam points

Determine the magnetic force and circular-motion conditions for a charged particle in a uniform magnetic field.
Use qvB=mv²/r to calculate radius, period, frequency, speed or mass-to-charge relationships.
Explain why magnetic force changes direction but not speed or kinetic energy when perpendicular to velocity.

[Maximum number: 4]

(a)

A proton moves on a circular path in a region of uniform magnetic field of magnetic flux density B that is directed into the plane of the page.

[ 4 ]

(i)

On the diagram, draw an arrow to indicate the velocity of the proton at the position shown.

[ 1 ]

(ii)

Show that the frequency of revolution of the proton is given by $f=\frac{e B}{2 \pi m_{\mathrm{p}}}$ .

[ 3 ]

$\begin{aligned} e v B=\frac{m_{\mathrm{p}} v^{2}}{R} f=\frac{1}{T}=\frac{v}{2 \pi R} \end{aligned}$

Both q and e are acceptable for the
charge.

[3]

Algebra leading to required expression $\boldsymbol{<}=\frac{e B}{2 \pi m_{\mathrm{p}}} \boldsymbol{} \boldsymbol{}$

All question bank results loaded

IB Physics SL D 3 2 Charge in Magnetic Fields Questions question 1

Question (a)

Question (i)

Question (ii)