Definitons Electrons, waves and photons

Question 1

coulomb

Answer 1

the charge transferred by a 1 ampere current in one second

Question 2

volt

Answer 2

1 joule per coulomb

Question 3

ohm

Answer 3

the resistance when 1 volt of potential difference produces 1 ampere of current

Question 4

kilowatt-hour (kW h)

Answer 4

the energy transferred by a 1 kW device in a time of 1 hour

Question 5

electronvolt (eV)

Answer 5

the energy transferred by an electron travelling through a potential difference of 1 V

Question 6

electric current

Answer 6

flow of charge per unit time

Question 7

number density

Answer 7

the number of charged particles per unit volume

Question 8

resistance

Answer 8

p.d/current

Question 9

resistivity

Answer 9

(Resistance x cross sectional area) / length

Question 10

power

Answer 10

work done per unit time

Question 11

potential difference

Answer 11

energy transferred per unit charge from electrical energy into other forms (e.g. light or heat)

Question 12

electromotive force

Answer 12

energy transferred per unit charge into electrical energy from other forms (e.g. chemical)

Question 13

internal resistance

Answer 13

Some energy is lost as heat in the battery; it behaves as if it has an internal resistance

Question 14

terminal p.d.

Answer 14

the potential difference measured across the terminals of an e.m.f. source

Question 15

displacement

Answer 15

distance moved from equilibrium of a point on a wave

Question 16

amplitude

Answer 16

maximum displacement

Question 17

wavelength

Answer 17

the distance between two adjacent peaks and troughs

Question 18

period

Answer 18

the time taken for one complete oscillation of a particle

Question 19

phase difference

Answer 19

the fraction of a cycle (measured in degrees) between the oscillations of two particles

Question 20

path difference

Answer 20

the difference in the distances travelled by two waves from coherent sources at a particular point

Question 21

frequency

Answer 21

number of wavelengths passing a point per unit time

Question 22

speed of a wave

Answer 22

distance travelled by the wave per unit time

Question 23

work function

Answer 23

minimum energy to release an electron from the surface of a metal

Question 24

threshold frequency

Answer 24

the minimum frequency of electromagnetic radiation that will release an electron from the surface of a metal

Question 25

Conventional current

Answer 25

moves from positive to negative terminals of battery

Question 26

electron flow

Answer 26

moves from negative to positive terminals of battery

Question 27

Kirchoff’s first law

Answer 27

sum of current into a junction equals the sum of current out; charge is conserved

Question 28

Kirchoff’s second law

Answer 28

sum of e.m.f.s around a loop = sum of p.d.s around the same loop; energy is conserved

Question 29

mean drift velocity

Answer 29

the average speed of charged particles along the length of a conductor

Question 30

Ohm’s law

Answer 30

for a metallic conductor at a constant temperature, the voltage is proportional to the current

Question 31

progressive wave

Answer 31

Waves that transfer energy away from a source without transfering material as a result of osicllations.

Question 32

stationary wave

Answer 32

superposition of 2 progressive waves with the same wavelength, moving in opposite directions

Question 33

longitudinal wave

Answer 33

Osscilation moving paralel to the direction the wave is travelling in

Question 34

transverse wave

Answer 34

Osscilation moving perpendicular to the direction the wave is travelling in

Question 35

refraction

Answer 35

the change in direction of a wave as it crosses an interface between two materials where its speed changes

Question 36

diffraction

Answer 36

wavefronts spread out after passing through a gap or around an obstacle

Question 37

intensity

Answer 37

the rate of flow of energy per unit area at right angles to the direction of travel of the wave. Measured in Wm^-3

Question 38

plane polarised wave

Answer 38

a transverse wave that vibrates in one plane only

Question 39

superposition

Answer 39

When 2 or more waves of the same type meet, the resultant wave can be found by adding the displacments of the individual waves

Question 40

interference

Answer 40

Superposition of coherent waves so there’s a change in overall displacement

Question 41

constructive interference

Answer 41

when two waves reinforce to give increased amplitude

Question 42

destructive interference

Answer 42

when two waves cancel to give reduced amplitude

Question 43

coherence

Answer 43

constant phase difference between waves

Question 44

node

Answer 44

where the amplitude is always zero

Question 45

antinodes

Answer 45

where the amplitude of the standing wave takes the maximum possible value

Question 46

photon

Answer 46

a packet of energy

Question 47

photoelectric effect

Answer 47

instantaneous emission of electrons from a metal surface when photons are incident on the surface