1. The Effect Of A Magnetic Field On Charged Particles

2. Extract From Specification
Moving charges in a magnetic field
Force on charged particles moving in a magnetic field.
F = B Q v, when the field is perpendicular to velocity.
Circular path of particles; application in devices such as the cyclotron.

3. deflecting charged particles
Electric currents are no more than flows of charged particles in conductors, so it is no surprise that magnetic fields can deflect the paths of moving charged particles. S
Thrust
Field + N
Current

4. deflecting charged particles
When negatively charged particles flow, the conventional current is in the opposite direction. S
Field - N
Current
Thrust

5. deflecting charged particles
The effect on a particle with a steady velocity is to push it in a circular path at right angles to the field. The path returns to a straight line when it emerges from the field S v - - N F
This has the implication that
Energy is not transferred by the field to the particle as the force on the particle is always at right angles to the direction of its travel. This always the case in circular motion. (However later we will see that accelerating electrons always emit some electromagnetic radiation. radiation)

6. The charge on the particle is q and its mass is mv r
The force towards the centre is also given by
Because the particle is undergoing circular motion, the force towards the centre is:
B = magnetic flux density (T)
q is the charge (C) on the particle. (If the particle is an electron this symbol is written as e)
v is the velocity of the particle (ms-1)

7. Electrons are deflected by a magnetic field within an evacuated tube.
High Voltage + -
Heated Cathode(-)

8. The Thompson Tube

10. The mass spectrometer

11. The mass spectrometer Can be used to identify different isotopes.
(in the simplest case H-1 and H-2) + + n
Both ions have a charge of +1 but one has more mass than the other.
If a mixed sample is injected into a magnetic field, the less massive ion will be deflected most.