component 2

Question 1

Efficiency of a system

Answer 1

% efficiency = (useful work out) / (work put in) X 100

Question 2

Potential difference (pd), V

Answer 2

Potential difference is the difference in the amount of energy that charge carriers have between two points in a circuit.

Question 3

Ohm’s law

Answer 3

The current in a metal wire at constant temperature is

proportional to the pd across it.

Question 4

Superconducting transition temperature, Tc

Answer 4

The temperature at which a material, when cooled, loses all its electrical resistance, and becomes super-conducting. Some materials (e.g. copper) never become superconducting however low the temperature becomes.

Question 5

The law of conservation of charge

Answer 5

Electric charge cannot be created or destroyed, (though positive and negative charges can neutralise each other). Charge cannot pile up at a point in a circuit.

Question 6

Emf, E

Answer 6

The emf of a source is the energy converted from some other form (e.g. chemical) to electrical potential energy per coulomb of charge flowing through the source.

Question 7

Capacitor

Answer 7

A capacitor is a pair of conducting plates separated by an insulator. If a potential difference is placed across the plates, they acquire equal and opposite charges.

Question 8

Dielectric

Answer 8

Insulator between the plates of a capacitor, also serving to make the capacitance larger than if there were just empty space.

Question 9

Hooke’s law

Answer 9

The tension in a spring or wire is proportional to its extension from its natural length, provided the extension is not too great (doesn’t exceed elastic limit)

Question 10

Ductile material

Answer 10

A material which can be drawn out into a wire. This implies that plastic strain occurs under enough stress.

Question 11

Elastic limit

Answer 11

This is the point at which deformation ceases to be elastic. For a specimen it is usually measured by the maximum force, and for a material, by the maximum stress, before the strain ceases to be elastic.

Question 12

Brittle material

Answer 12

Material with no region of plastic flow, which, under tension, fails by brittle fracture

Question 13

Newton’s law of gravitation

Answer 13

The gravitational force between two particles is proportional to the product of their masses, m1 and m2, and inversely proportional to their separation squared, r^2

Question 14

Coulomb’s law

Answer 14

The electrostatic force, F, between two small bodies is

proportional to the product of their charges, Q1 and Q2, and inversely proportional to their separation squared, r^2.

Question 15

Electric field strength, E

Answer 15

The force experienced per unit charge by a small positive charge placed in the field. This is a vector quantity.

Question 16

Gravitational field strength, g

Answer 16

The force experienced per unit mass by a mass placed in the field. This is a vector quantity

Question 17

Electric potential, VE

Answer 17

Electric potential at a point is the work done per unit charge in bringing a positive charge from infinity to that point. (scalar)

Question 18

Gravitational potential, Vg

Answer 18

Gravitational potential at a point is the work done per unit mass in bringing a mass from infinity to that point. (scalar)

Question 19

Black Body

Answer 19

A black body is a body (or surface) which absorbs all the electromagnetic radiation that falls upon it. No body is a better emitter of radiation at any wavelength than a black body at the same temperature.

Question 20

Absolute or kelvin temperature

Answer 20

At 0 K (-273.15°C) the energy of particles in a body is the lowest it can possibly be

Question 21

Boyle’s Law

Answer 21

pV is a constant : at constant temperature pressure and volume of a gas are inversely proportional

Question 22

Charles’s Law

Answer 22

V/T is constant : at constant pressure the volume of a gas is directly proportional to temperature

Question 23

Pressure Law

Answer 23

p/T is constant : at a constant volume the pressure of a gas is directly proportional to temperature

Question 24

Brownian Motion

Answer 24

• particles suspended in a fluid move randomly as a result of collisions with fast randomly moving particles
• random motion is where particles have a range of speeds and no preferred direction of movement

Question 25

Kepler’s laws of planetary motion: 1

Answer 25

Each planet moves in an ellipse with the Sun at its focus.

Question 26

Kepler’s laws of planetary motion: 2

Answer 26

The line joining a planet to the centre of the Sun sweeps out equal areas in equal times.

Question 27

Kepler’s laws of planetary motion: 3

Answer 27

T^2, the square of the period of the planet’s motion, is
proportional to r^3, in which r is the semi-major axis of its ellipse. [For orbits which are nearly circular, r may be taken as the mean distance of the planet from the Sun.]

Question 28

Kirchoff’s first law

Answer 28

Kirchhoff’s current law (1st Law) states that current flowing into a node (or a junction) must be equal to current flowing out of it. This is a consequence of charge conservation.

Question 29

Kirchoff’s second law

Answer 29

Kirchhoff’s voltage law (2nd Law) states that the sum of all voltages around any closed loop in a circuit must equal zero. This is a consequence of charge conservation and also conservation of energy.

sum of the EMF’s = sum of PD’s

Question 30

Current

Answer 30

Current is the rate of flow of charge, and travels in the direction that a positive test charge would