Fields And Their Consequences

Question 1

What is back EMF?

Answer 1

An emf generated by the coil in an AC generator that acts against the potential difference that has been supplied to the motor.

Question 2

What is capacitance?

Answer 2

The charge stored per unit pd in a capacitor?

Question 3

What is a capacitor?

Answer 3

An electrical component that stores charge. A parallel-plate capacitor is made of two parallel conducting plates with an insulator between them (dielectric).

Question 4

What is Coulomb’s Law?

Answer 4

The size of the forced that acts between two point changes is proportional to the product of their charges and inversely proportional to the square of their separation. It is attractive for opposite charges and repulsive for like charges.

Question 5

What is a cyclotron?

Answer 5

A particle accelerator made up of two 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 6

What does dielectric mean?

Answer 6

An insulating material placed between the two plates of a capacitor in order to increase the amount of charge it can store.

Question 7

What is an electrical conductor?

Answer 7

A material that contains freer electrons that are able to move throughout the material and carry charge.

Question 8

What is an electrical insulator?

Answer 8

A material that does not contain any free electrons. All electrons in an insulator are part of the individual atoms that make it up.

Question 9

What is an electric field?

Answer 9

A region surrounding a charged object which causes a force to be exerted on any charged object placed within the field.

Question 10

What is electric field strength?

Answer 10

The force per unit positive charge exerted on a charged object p;aced at that point in the field. This is a vector acting in the same direction as the force on a positive charge.

Question 11

What is electric potential?

Answer 11

The work done per unit charge on a positive test charge in bringing it from infinity to that point in the field.

Question 12

What is electromagnetic induction?

Answer 12

When an emf is induces in a wire/conducting rod when it is moved relative to the magnetic field.

Question 13

What is equipotential?

Answer 13

A surface of constant potential. No work is done by the field when an object moves along an equipotential.

Question 14

What is escape velocity?

Answer 14

A surface of constant potential. No work is done by the field when an object moves along an equipotential.

Question 15

What is escape velocity?

Answer 15

The minimum velocity required by an object to be able to escape a gravitational field of a mass when projected vertically from its surface.

Question 16

What is Faraday’s Law?

Answer 16

The magnitude of the induced emf is equal to the rate of change of flux linkage through the circuit.

Question 17

What is a field line/line of force?

Answer 17

A line representing the path that a North Pole (magnetic field), positive charge (electric field) or mass (gravitational field) would take when placed in the field.

Question 18

What is a force field?

Answer 18

An area in which an object will experience a non-contact force.

Question 19

What is a geostationary satellite?

Answer 19

A satellite that orbits above the equator with a 24 hour period, so it will always remain above the same position on the Earth. They orbit approximately 36,000km above the surface of the Earth.

Question 20

What is a gravitational field?

Answer 20

A regional surrounding a mass in which any other object with mass will experience an attractive force.

Question 21

What is gravitational field strength?

Answer 21

The force per unit mass exerted on a small test mass placed within the field.

Question 22

What is gravitational potential energy?

Answer 22

The component of an object’s energy due to its position in a gravitational field.

Question 23

What is Kepler’s Third Law?

Answer 23

The square of an object’s orbital period (T) is directly proportional to the cube of its orbital radius.

Question 24

What is Lenz’s Law?

Answer 24

An induced current is always in a direction so as to oppose the change that caused it.

Question 25

What is a magnetic field?

Answer 25

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

Question 26

What is magnetic flux?

Answer 26

A value which describes the magnetic field or field lines passing through an area. It is the product of magnetic flux density and the perpendicular area it passes through.

Question 27

What is magnetic flux density?

Answer 27

The force per unit current per unit length on a current-carrying wire placed at 90° to the field lines. Sometimes also referred to as the magnetic field strength.

Question 28

What is magnetic flux linkage?

Answer 28

The magnetic flux multiplied by the number of turns, N, of the coil.

Question 29

What is the motor effect?

Answer 29

When a current-carrying wire is placed within a magnetic field (non-parallel to the field lines) and experiences a force perpendicular to both the wire and the field lines.

Question 30

What is the permittivity of free space?

Answer 30

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

Question 31

What does polarised mean?

Answer 31

An atom/molecule becomes polarised when an external electric field causes the negative electron cloud to be shifted in the opposite direction to the positive nucleus - the charges are pulled in opposite directions. (This is what happens to the molecules of the dielectric in a capacitor).

Question 32

What is potential gradient?

Answer 32

The change of potential per metre at a point in the field.

Question 33

What is the radial field?

Answer 33

A field in which the field lines are all directed towards a single point (e.g. the centre of a planet or a point charge).

Question 34

What is relative permittivity?

Answer 34

The ratio of charge stored in a capacitor with the dielectric to charge stored without the dielectric. Also sometimes referred to as the dielectric constant.

Question 35

What is a step-down transformer?

Answer 35

A device made of two insulated wires coiled around an iron core in which the output voltage is smaller than the input outage due to the secondary coil having fewer turns than the primary coil.

Question 36

What is a step-up transformer?

Answer 36

A device made of two insulated wires coiled around an iron core in which the output voltage is greater than the input voltage due to the secondary coil having more turns than the primary coil.

Question 37

What is the synchronous orbit?

Answer 37

An orbit in which the period of the orbit is equal to the rotational period of the object that it is orbiting.

Question 38

What is the time constant?

Answer 38

The time taken for a capacitor to discharge 37% of its initial charge. The time constant is equal to the product of the capacitance and the resistance of the fixed resistor (that the capacitor is being discharged through).

Question 39

What is a uniform field?

Answer 39

A field in which all of the field lines are parallel and equally spaced - field strength is equal in all areas of the field.