Electric and Magnetic Fields

Question 1

What is V?

Answer 1

Electric potential

Question 2

E=V/d what is V?

Answer 2

Potential Difference

Question 3

In E = V/d, what is E?

Answer 3

Electric potential energy

Question 4

What is electric potential?

Answer 4

Work done per unit charge in bringing up a small positive test charge from infinity to that point by any path.

Question 5

How to work out magnetic field in a wire with concentric circles?

Answer 5

Right hand grip rule

Question 6

Two methods of producing a uniform electric field?

Answer 6

Passing current through a solenoid (uniform at centre), two opposite magnetic poles close together

Question 7

Southish coil direction of current?

Answer 7

Clockwise

Question 8

Northish coil direction of current?

Answer 8

Anticlockwise

Question 9

Which type of current is the split ring commutator for?

Answer 9

Direct current

Question 9

Which type of current is are the slip rings for?

Answer 9

Alternating current

Question 10

Which particle in a field can be modelled using projectile motion?

Answer 10

Charged particle in an electric field

Question 11

Which particle in a field can be modelled using circular motion?

Answer 11

Charged particle in a magnetic field.

Question 12

What is the Faraday-Neuman Law?

Answer 12

The size of e.m.f induced is directly proportional to the rate of cutting flux/change of flux linked

Question 13

What is Lenz’ Law?

Answer 13

The direction of the induced e.m.f is so as to oppose the effect inducing it.

Question 14

Which law proves conservation of charge?

Answer 14

Kirchoff’s First Law

Question 15

For magnetic flux through a coil (BANcosx), which angle?

Answer 15

cos angle between magnetic field line and normal to plane of coil

Question 16

What kind of current do cells and batteries supply?

Answer 16

Direct current

Question 17

What is a positron?

Answer 17

Mass same as electron, charge of +e

Question 18

In a transformer, which quantity is basically the same for all coils?

Answer 18

Magnetic flux

Question 19

In a transformer, which coil has the greatest magnetic flux density?

Answer 19

Coil with least turns

Question 20

In a transformer, which coil has the greatest magnetic flux linkage?

Answer 20

Coil with most turns

Question 21

What is Coulomb’s Law?

Answer 21

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

Question 22

What is an electric field?

Answer 22

a region where a charged object will experience a force at a distance

Question 23

What is electric field strength?

Answer 23

the force experienced per unit positive charge

Question 24

What does it mean to “ignore edge effects”?

Answer 24

Assume field is uniform, lines are straight and parallel

Question 25

What is a magnetic field?

Answer 25

the region surrounding a magnet or current carrying conductor in which magnetic objects experience a force

Question 26

In F=BILsinx, what is x?

Answer 26

Angle between field line and direction of current

Question 27

What is Φ?

Answer 27

flux - no. field lines, measured in Webers

Question 28

What is Ψ?

Answer 28

Flux linkage - the amount of field passing through a coil with N turns, measured in Wb-turns.

Question 29

How does a particle moving faster affect r?

Answer 29

r is bigger

Question 30

How does a more massive particle affect r?

Answer 30

r is bigger

Question 31

How does a stronger magnetic field affect r?

Answer 31

r is smaller

Question 32

How does a greater charge on the particle affect r?

Answer 32

r is smaller

Question 33

How can we show that time period is independent of particle’s velocity?

Answer 33

Eliminate r from equation for time period (2πr/v)

Question 34

Which directions do the fields go in a velocity selector?

Answer 34

Electric field is perpendicular to motion, and magnetic field is either in or out of page

Question 35

Why is a large e.m.f induced when a solenoid is switched off?

Answer 35

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.

Question 36

How to increase efficiency of a transformer?

Answer 36

Use low resistance windings, laminated iron to minimise induced eddy currents, use soft iron as it is easy to de/magnetise

Question 37

What is a search coil?

Answer 37

coil of insulated wire connected to galvanometer

Question 38

What are three differences between electric and gravitational fields?

Answer 38

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

Question 39

What is magnetic flux density?

Answer 39

The force on one metre of wire carrying a current of one amp at right angles to the magnetic field

Question 40

What is a Weber?

Answer 40

A change in flux linkage of one weber per second will induce an e.m.f. of one volt

Question 41

State and explain a factor that might affect the tensile strength of an ionic material.

Answer 41

Ionic separation because this affects breaking force.

Question 42

What is the kinetic energy of a particle being accelerated through an electric field?

Answer 42

VQ