Fields

Question 1

Describe Newton’s law in words.

Answer 1

• Force due to gravity is always attractive
• Force due to gravity is directly proportional to product of 2 masses
• Force due to gravity is inversely proportional to the square of the distances between centres of mass

Question 2

Define gravitational field strength of a point

Answer 2

The gravitational force per unit mass experienced by a test mass placed at that point.

Question 3

Electric Field

Answer 3

A region in space where a charged particle will experience a force.

Question 4

Electric Field Line

Answer 4

Direction that a positive test charge will accelerate.

Question 5

Permittivity of free space

Answer 5

A measure of the ability of a vacuum to allow an electric field to pass through it.

Question 6

Electric Potential Energy

Answer 6

The work done by an external force in bringing the charge from infinity to that point in the field.

Question 7

Electric Potential

Answer 7

Work done per unit charge on a positive test charge in moving the charge from infinity to that point

Question 8

Lines of equipotential

Answer 8

Line joining points of equal potential, which are at right angles to field lines.

Question 9

Magnetic Field

Answer 9

A region surrounding a magnet or current carrying wire that will exert a force on any other magnet or current carrying wire within it.

Question 10

Motor Effect

Answer 10

When a current carrying wire is placed perpendicular to a magnetic field and experiences a force perpendicular to both the wire and the field line.

Question 11

Magnetic Flux Density

Answer 11

Magnetic flux per unit area.

Question 12

When does F=BIL apply

Answer 12

When the wire is perpendicular to the magnetic field.

Question 12

Direction of field lines of bar magnet

Answer 12

North to south.

Question 13

Tesla

Answer 13

The flux density that produces a force of 1N in a wire of length 1m with 1A of current.

Question 14

Circular motion equation

Answer 14

r = mv/Bq

Question 15

Cyclotron

Answer 15

A particle accelerator made up of 2 D shaped electrodes positioned opposite each other. The electric field changes direction each time a particle moves from one electrode to the other causing the particle to accelerate.

Question 16

Weber

Answer 16

The magnetic flux through a surface if a magnetic field of flux 1T exists perpendicular to an area of 1m^2.

Question 17

Magnetic Flux Linkage

Answer 17

The product of the number of turns of the coil and the magnetic flux linking each turn in Webers.

Question 18

Electromagnetic Induction

Answer 18

When an emf is induced in a wire when it is moved relative to a magnetic field. Perpendicular motion induces greatest emf.

Question 19

Induced emf

Answer 19

The induction of an emf by way of cutting a magnetic field with an electric conductor.

Question 20

Faraday’s Law

Answer 20

Induced emf is directly proportional to to the rate of change of magnetic flux linkage.

Question 21

Lenz’s Law

Answer 21

The direction of the induced emf is such that it will oppose the change that is producing it.

Question 22

Transformer

Answer 22

A device that can change the potential difference of an alternating current. Made from 2 coils of wire, a primary and secondary coil. The coils are wound around an iron core.

Question 23

Step up/down transformer

Answer 23

A device made of 2 insulated wires coiled around an iron core in which the output voltage is greater/smaller than the input voltage, due to secondary coil having more/less coils than primary coil.

Question 24

Eddy current

Answer 24

Emf induced in the core of a transformer due to changing magnetic field. Current flows in the transformer core as it is made from conducting material.

Question 25

Transformer core

Answer 25

Provides greater increase of magnetic flux linkage.

Question 26

Transformer Laminations

Answer 26

Laminations are made from thin insulator which reduces eddy currents. Thin laminations of iron are used so smaller emf induced in core.

Question 27

Gravitational Potential Energy

Answer 27

The work done by an external force in bringing a mass from infinity to that point.

Question 28

Gravitational Potential

Answer 28

The work done per unit mass by an external force in bringing a mass from infinity to that point.

Question 29

Uniform gravitational field change in potential

Answer 29

delta V = g * delta h

Question 30

GPE in a non uniform field

Answer 30

E = (-GMm / r)

Question 31

Geostationary Orbit

Answer 31

-Orbits around the equator -Always stays above the same point above Earth -Orbits in same direction as Earth rotates -Orbital time period of 24 hours

Question 32

Geostationary orbit use

Answer 32

Telecommunications

Question 33

Low polar orbit

Answer 33

-Orbits above poles -Orbits much closer to Earth -Orbital time period of 90 - 105 minutes -High resolution pictures due to close distance

Question 34

Low polar orbit uses

Answer 34

-Spying -Weather forecasting

Question 35

Kepler's Third Law

Answer 35

The square of the time period of a body in a circular orbit is directly proportional to the cube of the radius of its orbit.

Question 36

Capacitor

Answer 36

An electrical component that stores charge. A parallel plate capacitor is made of 2 parallel conducting plates with an insulating dielectric between them.

Question 37

Dielectric

Answer 37

An insulating material between the 2 plates of a capacitor. The dielectric increases the amount of charge the plates can store. When the voltage becomes too high, electrons jump between the plates through the dielectric. Oiled paper is a common dielectric used in capacitors.

Question 38

Capacitance

Answer 38

The amount of charge that a capacitor stores for each volt of potential difference between the plates. C= Q/V

Question 39

Farad

Answer 39

The capacitance of a capacitor in which 1 Coulomb of charge causes a potential difference of 1 Volt.