CAIE A-Level Physics 20.3.2 Using F = BQv sin θ

Practise calculating magnetic force on moving charges with F = BQv sin theta, rearranging the relationship and interpreting force direction and magnitude.

Exam points

calculate force on a moving charge using F = BQv sin theta
rearrange the equation to determine B, Q, v or angle and use consistent units
interpret the direction and magnitude of force for charged particles

[Maximum number: 2]

A uniform magnetic field is now applied in the region of the electric field in Fig. 5.1, so that the electron in (b)(iii) travels undeviated through the region.

Determine the flux density B of the uniform magnetic field. Give a unit with your answer.
B= unit

E q=B q v

C1

$\begin{aligned} B =E / v=\left(6.4 \times 10^{3}\right) /\left(2.6 \times 10^{7}\right) =2.5 \times 10^{-4} \mathrm{~T} \end{aligned}$

A1

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20.3.2—F = BQv sin θ question 1