Paper 2 Magnetic Force Drills

Q1 Force on a Wire

A straight wire of length $0.080\mathrm{m}$ carries current $3.5\mathrm{A}$ perpendicular to a uniform magnetic field of flux density $0.42\mathrm{T}$.

1. Calculate the force on the wire. [2]
2. State how the force changes if the wire is turned parallel to the field. [1]
3. State the rule used to find force direction. [1]

Q2 Charged Particle in a Magnetic Field

An electron enters a uniform magnetic field of flux density $0.030\mathrm{T}$ with speed $4.0\times 10^6\mathrm{m}{\mathrm{s}}^{-1}$ perpendicular to the field. Take $e=1.60\times 10^{-19}\mathrm{C}$ and $m_e=9.11\times 10^{-31}\mathrm{kg}$.

1. Calculate the magnetic force magnitude. [2]
2. Calculate the radius of the circular path. [3]
3. Explain why the electron speed remains constant. [2]

Q3 Velocity Selector

Crossed electric and magnetic fields have $E=6.0\times 10^4\mathrm{V}{\mathrm{m}}^{-1}$ and $B=0.20\mathrm{T}$.

1. Calculate the speed of particles that pass through undeflected. [2]
2. Explain why particles with a different speed are deflected. [2]