Key Definitions

Question 1

Define EMF.

Answer 1

The amount of electrical energy produced by a battery/source per unit of charge.

Question 2

Define Power.

Answer 2

The rate of transfer of electrical energy to a component per second.

Question 3

Define Resistance.

Answer 3

Potential difference divided by the current, ie. the electrical energy used when a current of 1A moves through a component.

Question 4

Define Potential Difference.

Answer 4

The amount of electrical energy converted or transferred per unit of charge between 2 points.

Question 5

Define Ohm’s law.

Answer 5

The current passing through a conductor is proportional to the voltage as long as the physical conditions remain constant.

Question 6

Define Resistivity.

Answer 6

Resistance in Ohms multiplied by the cross-sectional area in metres squared divided by the length of the object in m.

Question 7

Define Critical/Transition Temperature.

Answer 7

The temperature that below which a superconductor has no resistance, so large currents can pass through it with no energy loss.

Question 8

Define Internal Resistance.

Answer 8

An electrical source or cell’s opposition to the flow of charge through it, defined as the loss of pd per unit current when a current passes through the source/cell.

Question 9

Define Isotope.

Answer 9

Nuclides with the same number of protons but different numbers of neutrons.

Question 10

Define Pair Production.

Answer 10

When a particle and its corresponding antiparticle are produced from a photon with energy greater than the total rest energy of the 2 particles.

Question 11

Define Annihilation.

Answer 11

When a particle and its corresponding anti-particle collide, converting all of their energy and mass into 2 high energy photons.

Question 12

Define Moment.

Answer 12

Force multiplied by perpendicular distance between the pivot point and the line of action of the force.

Question 13

Define Principle of Moments

Answer 13

States that for an object to be in equilibrium, the sum of the anticlockwise moments = the sum of the clockwise moments.

Question 14

When is an object in equilibrium?

Answer 14

When the sum of anticlockwise moments = sum of clockwise moments and all vertical forces cancel and all horizontal forces cancel.

Question 15

Define Couple.

Answer 15

A pair of equal and opposite forces separated by distance, d, acting about point, p: the turning effect at point p is equal to one of the forces multiplied by the perpendicular distance between the forces.

Question 16

Define Centre of Mass.

Answer 16

Where all of an object’s mass appears to act about and moments cancel.

Question 17

Define Newton.

Answer 17

Force required to accelerate 1kg by 1ms^-2

Question 18

Define the Law of Conservation of Energy

Answer 18

Energy is never created or destroyed, just transferred between different types.

Question 19

Define Hooke’s Law.

Answer 19

The extension of a spring is proportional to the force applied to it as long as the limit of proportionality is not exceeded.

Question 20

Define Stress.

Answer 20

Force per unit area.

Question 21

Define Strain.

Answer 21

Ratio of extension to original length.

Question 22

Define Young’s Modulus

Answer 22

Tensile stress divided by tensile strain; the stiffness constant of a material.

Question 23

Define Longitudinal Wave.

Answer 23

A propagating wave with oscillations in the same direction of propagation/energy transfer.

Question 24

Define Transverse Wave.

Answer 24

A propagating wave with oscillations perpendicular to the direction of propagation.

Question 25

Define Stationary Wave.

Answer 25

Formed when 2 waves of similar frequency travelling in opposite direction interfere and the resultant wave is the vector sum of each wave’s displacements at that point by the principle of superposition.

Question 26

Define Diffraction.

Answer 26

Spreading out of a wave when passed through a slit or around an obstacle.

Question 27

Define Coherent.

Answer 27

Same frequency and constant phase difference.

Question 28

Define Constructive Interference.

Answer 28

2 waves intersect and interfere through the principle of superposition and the resultant displacement is the vector sum of the 2 waves’ displacement at the point.

Question 29

What is the difference between single and double slit diffraction?

Answer 29

Single slit: Wide central maxima 2x width of others, and reduction in intensity going away; Double slit: Same width, going out.