Electric and Magnetic Fields Flashcards
What is V?
Electric potential
E=V/d what is V?
Potential Difference
In E = V/d, what is E?
Electric potential energy
What is electric potential?
Work done per unit charge in bringing up a small positive test charge from infinity to that point by any path.
How to work out magnetic field in a wire with concentric circles?
Right hand grip rule
Two methods of producing a uniform electric field?
Passing current through a solenoid (uniform at centre), two opposite magnetic poles close together
Southish coil direction of current?
Clockwise
Northish coil direction of current?
Anticlockwise
Which type of current is the split ring commutator for?
Direct current
Which type of current is are the slip rings for?
Alternating current
Which particle in a field can be modelled using projectile motion?
Charged particle in an electric field
Which particle in a field can be modelled using circular motion?
Charged particle in a magnetic field.
What is the Faraday-Neuman Law?
The size of e.m.f induced is directly proportional to the rate of cutting flux/change of flux linked
What is Lenz’ Law?
The direction of the induced e.m.f is so as to oppose the effect inducing it.
Which law proves conservation of charge?
Kirchoff’s First Law
For magnetic flux through a coil (BANcosx), which angle?
cos angle between magnetic field line and normal to plane of coil
What kind of current do cells and batteries supply?
Direct current
What is a positron?
Mass same as electron, charge of +e
In a transformer, which quantity is basically the same for all coils?
Magnetic flux
In a transformer, which coil has the greatest magnetic flux density?
Coil with least turns
In a transformer, which coil has the greatest magnetic flux linkage?
Coil with most turns
What is Coulomb’s Law?
any two point charges exert electrostatic force on each other that is directly proportional to the product of their charges and inversely proportional to separation squared
What is an electric field?
a region where a charged object will experience a force at a distance
What is electric field strength?
the force experienced per unit positive charge
What does it mean to “ignore edge effects”?
Assume field is uniform, lines are straight and parallel
What is a magnetic field?
the region surrounding a magnet or current carrying conductor in which magnetic objects experience a force
In F=BILsinx, what is x?
Angle between field line and direction of current
What is Φ?
flux - no. field lines, measured in Webers
What is Ψ?
Flux linkage - the amount of field passing through a coil with N turns, measured in Wb-turns.
How does a particle moving faster affect r?
r is bigger
How does a more massive particle affect r?
r is bigger
How does a stronger magnetic field affect r?
r is smaller
How does a greater charge on the particle affect r?
r is smaller
How can we show that time period is independent of particle’s velocity?
Eliminate r from equation for time period (2πr/v)
Which directions do the fields go in a velocity selector?
Electric field is perpendicular to motion, and magnetic field is either in or out of page
Why is a large e.m.f induced when a solenoid is switched off?
Coil is linked with its own magnetic field. When current is switched off, magnetic field collapses in a very short time and induces large e.m.f in opposite direction.
How to increase efficiency of a transformer?
Use low resistance windings, laminated iron to minimise induced eddy currents, use soft iron as it is easy to de/magnetise
What is a search coil?
coil of insulated wire connected to galvanometer
What are three differences between electric and gravitational fields?
Electric forces can be attractive/repulsive, gravitational fields are always attractive, objects can be shielded from electric fields, size of electric force depends on medium between charges, gravitational force makes no difference
What is magnetic flux density?
The force on one metre of wire carrying a current of one amp at right angles to the magnetic field
What is a Weber?
A change in flux linkage of one weber per second will induce an e.m.f. of one volt
State and explain a factor that might affect the tensile strength of an ionic material.
Ionic separation because this affects breaking force.
What is the kinetic energy of a particle being accelerated through an electric field?
VQ
