Different magnetic fields are present in the two chambers shown - AQA - A-Level Physics - Question 26 - 2018 - Paper 2

In a magnetic field, the radius of the circular path of a charged particle is given by the formula: $r = \frac{mv}{qB}$ where:

• $r$ is the radius of the circular path
• $m$ is the mass of the particle
• $v$ is the velocity of the particle
• $q$ is the charge of the particle
• $B$ is the magnetic field strength.

For the first chamber:

1. Let the mass be $m$, charge be $q$, and the magnetic field strength in the first chamber be $B_1$.
2. The radius $r_1$ is 200 mm (0.2 m) and initial velocity $v_1$ is 80 m s⁻¹. Thus: $0.2 = \frac{m \cdot 80}{qB_1}$

For the second chamber:

1. Let the radius in the second chamber be $r_2$ and the magnetic field strength $B_2$.
2. The radius $r_2$ is 100 mm (0.1 m), and we denote the speed in the second chamber as $v_2$. Thus: $0.1 = \frac{m \cdot v_2}{qB_2}$