7.0 Fields And Their Consequences

Question 1

Direction of field lines

Answer 1

From north to south or positive to negative

Question 2

What are field lines

Answer 2

A visual representation of a fields direction and strength

Question 3

What is potential energy in a field

Answer 3

The potential energy is the mass or charge has due to its position in a field

Question 4

What is gravitational potential

Answer 4

The work done per unit mass to move a small test mass from infinity to a point in a gravitational field

Question 5

Why is gravitational potential zero at infinity

Answer 5

At infinite, the grav field becomes negligible, so the work done to move the test charge is zero

Question 6

What is gravitational potential difference

Answer 6

The difference in gravitational potential between two points in the grav field

Question 7

What is an equipotential surface in gravitational fields

Answer 7

Surfaces in a field where all points have the same gravitational potential

Question 8

Properties of equipotential surfaces

Answer 8

No work is done to move along them and they are always perpendicular to field lines

Question 9

What is significant about the negative in the grav potential equation

Answer 9

shows that the potential is always negative, as gravitational forces always attract

Question 10

relation of orbital period and speed to radius

Answer 10

the square of the period if directly proportional to the cube of the radius

Question 11

What is the total energy of an orbiting body

Answer 11

it is always negative. the more negative, the lower the orbit

Question 12

What is escape velocity

Answer 12

The minimum speed an object must have to leave a grav field without requiring additional energy

Question 13

What must occur for escape in grav fields

Answer 13

the objects total energy must reach zero

Question 14

Letter for central body in grav fields

Answer 14

M

Question 15

Letter for object in grav fields

Answer 15

m

Question 16

What is a synchronous orbit

Answer 16

An orbit of period of that of the rotational period of the body it orbits

Question 17

Characteristics of synchronous orbits

Answer 17

Object remains fixed relative to a point on the central mass

Question 18

Conditions for a synchronous orbit

Answer 18

planet must have a fixed rotational period, orbital period = rotational period, must be circular

Question 19

What is LEO

Answer 19

Low Earth Orbit. Between 200 - 2000 km

Question 20

Uses of LEO

Answer 20

Observation, scientific research, communication, surveillance

Question 21

Use of geostationary orbits

Answer 21

communication and weather monitoring

Question 22

Define coulomb’s law

Answer 22

The magnitude of the force between two point charges is directly proportional to the product of the charges and inversely proportional to the square of the distance between

Question 23

What is the permittivity of free space

Answer 23

the value of the absolute dielectric permittivity of a vacuum

Question 24

When calculating force between charges, what can we do

Answer 24

Treat air as a vacuum

Question 25

Where is charge concentrated in a charged sphere

Answer 25

Radiating out from the centre

Question 26

Compare the magnitude of gravitational and electrostatic forces between subatomic particles

Answer 26

The electrostatic force is much greater than the gravitational force. Grav can be considered negligable in electrostatic calculation

Question 27

Define electric field strength

Answer 27

the intensity of an electric field at a particular point

Question 28

Define absolute electric potential

Answer 28

The work done per unit charge to move a small test charge from infinity to a point in an electric field

Question 29

Why is electric potential zero at infinity

Answer 29

At infinite, the electric field becomes negligible, so the work done to move the test charge is zero

Question 30

What is electric potential difference

Answer 30

The difference in electric potential between two points in the electric field

Question 31

What is an equipotential surface in electric fields

Answer 31

Surfaces in a field where all points have the same electric potential

Question 32

Define capacitance

Answer 32

The charge stored per unit potential difference

Question 33

What is a dielectric

Answer 33

an electrical insulator that can be polarised by an applied electric field

Question 34

How do dielectrics work

Answer 34

When in a field, the polarised molecules in the material rotating slightly to the opposite orientation to the field, creating another field that opposes the original one

Question 35

What is the dielectric constant

Answer 35

How many times more efficient the dielectric is at storing charge than a vacuum

Question 36

What is relative permittivity

Answer 36

the factor with which the electric field is decreased relative to vacuum

Question 37

What is the area below a charge - pd graph

Answer 37

The energy stored by the capacitor

Question 38

What is the time constant

Answer 38

RC

Question 39

What is the time to halve of a charged capacitor

Answer 39

0.69RC

Question 40

What is the force on a current carrying wire in a mag field

Answer 40

F = BIL when perpendicular to current

Question 41

Fleming's left hand rule

Answer 41

Thumb: Motion, Index finger: Field, Middle finger: Current

Question 42

What is magnetic flux density

Answer 42

The strength of a magnetic field defined by the density of field lines

Question 43

Definition of the tesla

Answer 43

The flux density that causes a force of 1 N on a 1 m wire carrying a current of 1 A at right angles to the field

Question 44

What is the force on a charged particle moving in a mag field

Answer 44

F = BQv when field if perpendicular to velocity

Question 45

Direction of positively charged particle in mag field

Answer 45

With field lines

Question 46

Direction of negatively charged particle in mag field

Answer 46

Against field lines

Question 47

Uses of mag fields

Answer 47

Circular path in cyclotron

Question 48

Define magnetic flux

Answer 48

The number of field lines passing through a region of space

Question 49

Define magnetic flux linkage

Answer 49

The magnetic flux for a multiple turn coil

Question 50

What is electromagnetic induction

Answer 50

The process where an emf is induced from a change in flux on the material

Question 51

Define Faraday's law

Answer 51

The magnitude of the induced e.m.f is directly proportional to the rate of change in magnetic flux linkage

Question 52

Define Lenz's law

Answer 52

The induced e.m.f acts in such a direction to produce effects that oppose the change causing it

Question 53

Applications of electromagnetic induction

Answer 53

Electric generators, Induction motors, Induction cooking

Question 54

What are sinusoidal voltages and currents

Answer 54

The voltage and current of AC. Where they oscillate periodically

Question 55

What is root mean square of the current and voltage

Answer 55

The average current and voltage of the AC graph

Question 56

What is the UK mains voltage

Answer 56

230V

Question 57

What is a transformer used for

Answer 57

To change the voltage of an AC

Question 58

What is a step up transformer

Answer 58

Increases voltage by having more secondary coils

Question 59

What is a step down transformer

Answer 59

decreases voltage by having less secondary coils

Question 60

Production of eddy currents in a transformer

Answer 60

due to changing magnetic flux, free electrons in the iron move due to the induced emf, creating a current

Question 61

Causes of inefficiencies in a transformer

Answer 61

Resistance in wires, induced eddy currents, poor insulation

Question 62

Reducing inefficiencies in a transformer

Answer 62

Laminating core, use soft iron, use thick wires