Magnetic Fields And Induction and electric and gravitational fields

Question 1

Lenz’s law

Answer 1

Lenz’s law states that the direction of the induced current is always such as to oppose the change that causes the current

Question 2

Root mean square value of alternating current

Answer 2

The value of direct current that would give the same heating effect as the alternating current in the same resistor

Question 3

Faraday’s law

Answer 3

Faraday’s law of electromagnetic induction states that the indices emf in a circuit is equal to the rate of change of flux linkage through the circuit

Question 4

Tesla definition

Answer 4

One Tesla is the magnetic flux density that causes a force of 1N to be exerted on every 1m length of wire carrying 1A of current in a direction that is perpendicular to the field

Question 5

Peak to peak voltage

Answer 5

Maximum on graph to minimum on graph

Question 6

Uses of cyclotron

Answer 6

Particle accelerator
Proton beam therapy
Medical imaging

Question 7

Reasons for inefficiency of transformer and their solutions

Answer 7

Energy lost as heat due to resistance of coils -> use wires with low resistance
Eddy currents flow in solid iron core as core itself is situated in changing magnetic field -> use laminated iron core
Energy loss due to hysteresis when magnetising and demagnetising core -> use soft magnetic material eg iron that is easily magnetised
Energy lost if not all the flux through the primary coil goes through the secondary coil -> wrap secondary coil around primary coil

Question 8

Force field

Answer 8

Region where body experiences non-contact force

Question 9

How do force fields arise?

Answer 9

Interaction of mass
Interaction of Static charge
Interaction between moving charges

Question 10

Similarities between electrostatic and gravitational forces

Answer 10

Inverse square laws
Use of Field lines
Use of potential concept
Équipotentiel surfaces

Question 11

Differences between gravitational and electric fields

Answer 11

Gravitational forces always attract, but charges can repel or attract

Question 12

What is gravity?

Answer 12

Universal attractive force acting between all matter

Question 13

Newton’s law of gravitation

Answer 13

States that there is an attractive force between any two masses which is proportional to the product of the masses and inversely proportional to the square of Their separation

Question 14

Gravitational field strength definition

Answer 14

Force per unit mass

Question 15

Define gravitational potential

Answer 15

The work done in bringing a mass from infinity to that point in the field

Question 16

Is potential a scalar or a vector?

Answer 16

Scalar

Question 17

Équipotentiel definition

Answer 17

Line or surface of equal potential

Question 18

Low orbit satellite uses

Answer 18

Imaging eg spying and weather

Question 19

Advantages of low orbit satellites

Answer 19

Require less powerful transmitters than higher orbit satellites
Cheap to launch
Close enough to see earth’s surface clearly

Question 20

Disadvantage of low orbit satellites

Answer 20

Multiple satellites working together are needed so that all areas of Earth stay connected

Question 21

Features of low orbit satellite

Answer 21

200km above Earth
Polar orbit
Relatively short time period

Question 22

Coulomb’s law

Answer 22

There is a force between two charges which is directly proportional to the product of the charges and inversely proportional to the square of the separation of the charges

Question 23

Electric field strength definition

Answer 23

Force per unit positive charge

Question 24

When charge moves with the field, what does work?

Answer 24

Field does work

Question 25

When charge moves against field, what does work?

Answer 25

Particle

Question 26

Electric potential definition

Answer 26

The potential at a point a distance r from a charge Q is defined as the work done in moving a unit positive charge from infinity to that point in the field

Question 27

One radian

Answer 27

Angle subtended at centre of a circle by an arc that is equal in size to the radius