EM Flashcards
Explain the direction of the magnetic force
Using FLEMING LEFT HAND RULE, since current is upwards and magnetic field is into the plane of the paper PERPENDICULAR to the current / velocity (for moving charged particles), direction of magnetic force is to the left of the current
What are the magnetic flux patterns around a straight wire, circular coil, bar magnet and solenoid ?
see S6 in 14A
What is a magnetic field
a region of space where a magnetic force is experienced by a long straight current carrying conductor / moving charged particle / permanent magnet
What does the magnetic field line symbolises ?
the direction of a magnetic field line arrow defines the direction of the magnetic force on a North Pole
What is then magnetic flux density / magnetic field strength ?
is defined as the force per unit length per unit current acting on a long straight current carrying conductor placed perpendicularly to the magnetic field
Definition of a Tesla
The magnetic flux density of the Bfield is one Tesla if a long straight current carrying conductor placed perpendicularly to the Bfield experiences a force per unit length of 1Nm-1 when the current is 1A
Explain the forces of 2 parallel current carrying conductors (in this case both diff directions) wire AB on the left w current moving up and wire CD on the right w current down
gentle reminder spacial arrangement of thumb is impt
using Right Hand Grip Rule, the current in AB produces a magnetic field at CD into the paper. Using Fleming Left Hand Rule, the wire at CD experiences a magnetic force directed away from AB as its current is travelling in a direction perpendicular to the B field. By Newtons 3rd Law OF MOTION, an equal and opposite force is exerted on AB by CD and both wires move away from each other
why is the speed of a charged particle in B field constant when it moves in a circular arc / helical path - learn how to draw (r constant) when e field and b field in same direction and e and b force both affects helical path direction / undeflected ; when velocity changes, shape is a spiral (r changes)
- Direction of motion of velocity is PERPENDICULAR to magnetic FORCE
- No work done by magnetic force (since force must act in direction of force for work to be done) on charged particle (during the circular motion) and kinetic energy and hence speed remains constant
Explain the movement of a moving charge
DONT SAY NO FORCE ACTING IS WRONG
- Magnetic force is acting in a direction perpendicular to velocity
- Hence there is no work done by the magnetic force
- There is constant speed as ke does not change
- FB= BqV, hence magnitude of FB is constant
- FB provides Fc
- Hence magnitude of Fc is aCONSTANT NOT DONT HAVE and there is UNIFORM circular motion
how do we strengthen the magnetic field in a solenoid
Insert a piece of soft iron (with ferrous core) into the solenoid and the resultant magnetic flux density at the poles of the solenoid will be enhanced as the permeability μ0 becomes μIron and B=μ0NI
desirable properties of a ferrous core
- high magnetic permeability
- easily magnetised with low dissipation in energy
- low electrical conductivity to reduce eddy currents
crossed fields in a velocity selector
a setup whereby an E field (f in direction for protons) and B field (f perp to direction) are perpendicular to each other such that they exert equal and opposite forces on a moving charge and hence causes no deflection of the particle (with speed E/B) as it experiences 0 net force
