Physics Unit 5 A2 OCR A revision
- Created by: Abbi
- Created on: 09-06-10 14:11
Physics Revision Unit 5
Electric and Magnetic Fields
Electric Fields:
Oppositely charged particles attract
Charged object in electric field – experience force
Coulomb’s Law: F = (kQ1Q2)/r2 where k = 1/4pie epsilom
Force on Q1 is equal and opposite to force on Q2
F = EQ
E in direction the positive charge would move in NC-1
Electric Field Strength is the force per unit charge
In a radial field E is inversely proportional to r2
Area under an E vs r graph is the electric potential
Field strength is the same everywhere in a uniform field
E=V/d E in Vm-1
Charged particle in uniform field – experiences a constant force parallel to the electric field lines
Positively charged- force in same direction as field lines
Particle accelerates at constant rate- Newton’s 2nd
Particle’s velocity has component at right angles to the field lines – particle will have uniform velocity – Newton’s 1st
Combined effect of constant acceleration and constant velocity at right angles is a parabola
Similarities between gravitational and electric fields:
· Both force per unit something
· Both inverse square laws
· Point mass/charge creates radial field
Differences:
· G force attractive. E force either attractive or repulsive
· Objects can be shielded from electric fields, not G fields
· Medium affects size of electric forces not G forces
Magnetic Fields:
Region where a force is exerted on magnetic materials
Field lines
North to south
Closer lines = stronger field
When current flows in wire – magnetic field around wire
Direction of magnetic field around a current-carrying wire can be worked out using the right-hand rule. Thumb current, fingers field.
Single coil or solenoid field
Current carrying wire in external magnetic field – fields interact
Form stretched catapult effect where flux lines are closer together
Cause force
Current parallel to flux lines – no force
Direction of the force is always perpendicular to both the current direction and the magnetic field – Fleming’s left hand rule. First = field, second = current, thumb = force/motion
F = Bil
Magnetic field strength – the force on one meter of wire carrying a current of one amp at right angles to the magnetic field
Also called flux density and measured in teslas, T
1 tesla = Wb/m2
Vector quantity
F = BIl sinθ
Charged Particles in Magnetic Fields:
Electric current – flow of negatively charged electrons
Affected by magnetic fields so current carrying wire experiences a force
I = qv/l
F = Bqv
Force on a moving charge in a magnetic field is always perpendicular to its direction of travel
Condition for circular motion
Effect used in particle accelerators, which use magnetic fields to accelerate particles to very high energies along circular paths
The radius of curvature of a path of a charged particle moving through a magnetic field gives you information about the particle’s charge and mass meaning you can identify different particles by studying how they…
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