Electric and Magnetic Fields Flashcards
(38 cards)
What is an inverse square law?
The electrostatic force between two charged spherical objects
What happens between two like and opposite charges
Like- repels opposite- attract
What is electric field strength and units? and what type of unit
E, at a point is the force per unit charge at that point Nc^-1, vector
Talk about field lines
The close they are, the stronger the field, they point towards the negative charge
Which direction is the field around a negative point charge directed
Inwards towards the charge, and around a spherical positive charge distribution it is directed radially outwards
What is an example of a non radial field and where is it found
Uniform electric field, it is found in the space between two parallel plates when there is a potential difference applied between the plates
What is a capacitor
A device that stores energy by separating charge. Placing charge on the capacitor in a potential difference
Units of capacitance? And what is definition.
A farad, 1F, 1CV^-1, it is a huge unit and normally ranges from mewf to pf. Amount of charge stored per volt. C=Q/V
When is a capacitor fully charged
When the potential difference across it becomes equal to the emf of the source
E
Energy is stored in the capacitor because work is done as charge moves through the net potential difference in the circuit. This becomes electrostatic potential energy
How do we measure the work done
The shaded area under the graph of potential difference between the plates v against the charge on the plates q. Area of triange half base times height so w=0.5QV and using C=Q/V you can change to different formulas when you make q and v subjects.
How do you discharge a capacitor? and what happens
Move the switch, as the charge decreases, so does the potential difference across the capacitor and hence also the current
What is the discharging process an example of?
Exponential decay
What is RC
Time constant of the circuit
What does a wire carrying a current have around it and what happens when wire is wound into a long solenoid.
a circular magnetic field and when wound into a long solenoid there is a uniform field inside . Parallel equally spaced field lines
What are lines representing the magnetic field called
lines of magnetic flux
3 things about the lines
Arrows indicate the forces that would act on a magnetic north pole
The lines are continuous and must not cross each other
The closer the lines, the stronger the magnetic field
What do the number of lines passing through a unit area perpendicular to the field represent
the flux density beta, and is measured in tesla, T. Flux omega is measured in webers, wb.
When will there be a maximum force in f=bilsintheta and what is the magnetic field strength B defined as?
when the current is at right angles to the direction of the field, the force on one metre of wire carrying a current of one amp at right angles to the magnetic field.
Charged particle beams- A charge q, moving with speed v through a magnetic field also experiences a magnetic force F, as long as there is a component of the field perpendicular to the direction of charge movement.
Again, when max force?
Maximum force will be when the charge movement is ar right angles to the direction of the field. F=BQvSintheta
When is an emf generated
When any conductor experiences a changing magnetic flux
What causes the changing magnetic flux
May be due to relative movement between the conductor and a magnetic field (dynamo effect).
Or because the conductor is in a region of varying magnetic field strength (the transformer effect)
What is flux linkage
For a conducting coil, the size of the effect increases with increasing turns of wire, knows as flux linkage.
N Omega, where n is the number of turns. The flux through the coil depends upon the angle of the normal to the plan of the coil to the field direction.
What is Faraday’s law
States that the magnitude of the emf, is directly proportional to the rate of change of flux linkage.
