current carrying wire experiences a force when its current is flowing perpendicularly to the direction of a magnetic field. similarly → a beam of moving charged particles would also experience a force when a magnetic field is applied perpendicularly to the beam of particles.
 |  |
|---|---|
| - this diagram shows the force acting on a positively charged particle → as it moves through a magnetic field. - the magnetic field shown is acting into the plane of the paper. - the direction of current is same as direction of motion of the charge, since charge is positive. - as the charge enters magnetic field, the direction of force on the charge is given by Fleming’s left hand rule and is perpendicular to the path of travel. - the resultant path is circular, with the force acting towards the centre of the circle. | - this diagram shows the force acting on a negatively charged particle in the same magnetic field. - in this case → direction of current is opposite to direction of motion of the charge. - using Fleming’s left hand rule → we can determine the motion as the charge enters the magnetic field. - direction of force on the charge is again perpendicular to the direction of travel, but in the opposite direction to that of previous diagram. - the resultant path is circular, with the force acting towards the centre of the circle. |
similar to a the current carrying conductor, the force acting on a charged particle:
- increases when the charge on the particle increases
- increases when the magnetic field increases
- is in the opposite direction if the particle is oppositely charged.
- is in the opposite direction if the direction of magnetic field or velocity of charged particle is reversed.
Important
- The current direction is the same as the direction of motion for a positive charge
- But for a negative charge, current is in the opposite direction
Important
conditions required for particle to experience a force in magnetic field
- particle must be charged (+ve or -ve)
- particle must be moving, and not be parallel to magnetic field