Physics Definitions - Unit 5

Electric field                         Electric fields are created by electric charges.  in an electric field a test charge will experience a force

Define Electric Field Strength        The electric field strength is the force per unit charge experienced by the test charge in the electric field

Describe how electric field Lines represent electric fields         Electric field lines show the direction that a positive test charge would move.  They go away from positive charges and towards negative charges.  If the field lines are close together the Electric field is stronger.  Parallel field lines show the Electric field is uniform 

Select  equation for Electric Field Strength of a point charge   The electric field around a charge Q is radial spreading out in all directions.  The field strength (E=F/q) at distance r from charge Q is given by

Select  equation for uniform Electric Field Strength between parallel charged plates          For parallel plates the electric field is uniform between the plates by considering work done moving between the plates as W=Fd and as W=qV it can be shown that the electric field strength depends only upon the potential difference V and the plate separation d. 

Explain the effect of a uniform electric field on charged particles        A charged particle q experiences a force F=Eq along the direction of the field lines.

Describe similarities and differences between gravitational fields of point masses and electric fields of point charges.

            Both fields fall off as

Both are radial field lines spreading out in all directions

Gravitational fields are always attractive ie towards the mass.

Electric field lines can be towards a positive charge or away from a negative charge

Electric fields act on charges, gravitational fields act on masses.

State and use Flemings left hand rule to determine the force on a current conductor placed at right angles to a magnetic field             .  Left hand.  First Finger field direction from North  to South.  Second finger current direction from + to -.  Thumb force direction.  Note the force is at right angles to the current and the field.

Define magnetic flux density and Tesla   B the magnetic flux density is defined by  ie flux density is the force per unit current per unit length on a current carrying wire at right angles to the magnetic field lines.

 Therefore  ie a Tesla is the flux density when a wire of length one metre carrying a current of one amp at right angles to the field experiences a force of 1 Newton

Analyse the circular orbits of charged particles moving in a plane perpendicular to a uniform magnetic field by relating the magnetic force to the centripetal acceleration it causes. A charge moving in a magnetic field experiences a force at right angles to its velocity.  A force at right angles to its velocity (i) will not change the speed of the particle as no work is done by the force (ii) makes the charge move in a circle. 

The centripetal force  is equal to the magnetic force F=BQv

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