# Comparing Charged Particles in Magnetic Fields to Electric Fields

This is part of the HSC Physics course under the topic Charged Particles, Conductors and Electric and Magnetic Fields.

### HSC Physics Syllabus

• compare the interaction of charged particles moving in magnetic fields to:

the interaction of charged particles with electric fields
other examples of uniform circular motion (ACSPH108)

### Charged Particle in Electric Field vs Magnetic Field

This video compares the interaction of charged particles moving in magnetic fields to that with electric fields.

### Comparison to Electric Fields

 Similarities Differences ·      Direction depends on nature of charge i.e. positive or negative ·      Magnitude of force is proportional to charge (q) of the particle and field strength (E and B) ·      Both are relatively greater than gravitational force. In other words, gravitational force is negligible when a particle is within either an electric or magnetic field ·      Type of force acting on the charged particle is different. Electrostatic force and magnetic force in electric and magnetic fields respectively ·      Stationary particle experiences force in an electric field but none in a magnetic field ·      Interaction with magnetic field can cause uniform circular motion ### Comparison to Other Uniform Circular Motion

So far, we have seen circular motion in examples such as:

• car driving around a curved path

• satellite/planets orbiting in space

• rollercoaster travelling around a 360º track

In these cases, the centripetal force is always supplied by a different force. For example, whilst the magnetic force drives circular motion for moving charges, friction does so for cars driving around bends.

The equations used to calculate these forces are also different. For example, the gravitational force in the circular motion of planets and satellites are calculated by:

$$F_g=\frac{GMm}{r^2}$$

However, all features of uniform circular motion are shared, including:

• direction of centripetal force is towards the centre of the motion
• linear velocity of the charged particle is constant in magnitude and orthogonal to the centripetal force
• the charged particle will continue to undergo circular motion as no additional work is required (W = 0)

Previous section: ﻿Charged Particles in Magnetic Fields