Photons And Electrons

Question 1

Pulse

Answer 1

a single disturbance that travels through a medium

Question 2

Transverse pulse

Answer 2

displacement of particles in medium is perpendicular to direction of pulse movement.

Question 3

Equilibrium/rest position

Answer 3

position of particles when no disturbance is passing over it

Question 4

Amplitude

Answer 4

magnitude of maximum displacement of particle from rest position

Question 5

Crest

Answer 5

top of pulse

Question 6

Pulse speed

Answer 6

distance travelled by crest per unit time.

Question 7

Factors affecting pulse speed

Answer 7

• depends only on properties of medium (density, tension etc.)
• does not depend on properties of pulse (amplitude, pulse length)

Question 8

Types of interference

Answer 8

• constructive interference
• destructive interference

Question 9

Wave

Answer 9

a series of disturbances that travel through a medium.

Question 10

Transverse wave

Answer 10

• vibration of particles in the medium is perpendicular to direction of motion of wave
• maximum and minimum positions on a transverse wave are called crests and troughs
• amplitude is the magnitude of maximum displacement from the equilibrium or rest position
• particle has completed 1 oscillation when in the same position and has the same motion as when it started

Question 11

Period (T)

Answer 11

time required to complete one full oscillation.

Question 12

Frequency (f)

Answer 12

number of oscillations per second (Hz).

Question 13

Factors affecting wave speed

Answer 13

• wave speed is not affected by properties of the wave (e.g. period, frequency, wavelength, amplitude)
• wave speed is affected by properties of the medium, (e.g. density)

Question 14

Longitudinal wave

Answer 14

the continuous propagation of disturbances through a medium, in which the particles of the medium oscillate in a direction parallel to the direction of motion of the wave.

Question 15

Compression

Answer 15

a place where the particles in the medium are packed closely together.

Question 16

Rarefaction

Answer 16

a place where the particles in the medium are stretched far apart.

Question 17

Wavelength

Answer 17

shortest distance between two successive points in phase.

Question 18

Pitch

Answer 18

describes how high or low a sound is, it depends on the frequency of the wave.
high pitch = high frequency
low pitch = low frequency

audible sound - within human hearing range
infrasound - below audible sound
ultrasound - above audible sound

Question 19

Electromagnetic waves

Answer 19

all travel at the speed of light, c, where c = 3,0×108 m⋅s−1 (in a vacuum)

Question 20

Types of electromagnetic waves

Answer 20

From lowest wavelength / highest E and f:
- gamma rays
- X-rays
- ultraviolet
- visible light (violet ~ 400nm ; red ~ 700nm)
- infrared
- microwaves
- radio waves

Question 21

Photon

Answer 21

a “parcel” of light with a quantum of energy

Question 22

Energy of a photon

Answer 22

is directly proportional to frequency of light.

Question 23

The hydrogen emission spectrum

Answer 23

blue - 434nm
blue-green - 486nm
red - 656nm

each coloured line:
- represents light with a single, unique wavelength and frequency
- contains photons with a specific quantum of energy

The dark bands indicate the absence of light at those wavelengths.

Question 24

Photoelectric effect

Answer 24

the process that occurs when light shines on a metal and electrons are ejected
OR
the ejection of electrons from a metal when light above a certain minimum frequency shines on it.

Question 25

Significance of photoelectric effect

Answer 25

it establishes the quantum theory and it illustrates the particle nature of light.

Question 26

Light

Answer 26

can behave as
- waves (e.g. when undergoing interference or diffraction)
- particles

Question 27

The photoelectric effect is proof that light has a particle nature

Answer 27

• light can be considered to be a stream of photons
• 1 e– can only absorb 1 photon
• if the photon has too little energy, no e– will be ejected, no matter how bright the light is

Question 28

Threshold (cut-off) frequency (fo)

Answer 28

the minimum frequency of incident radiation at which electrons will be emitted from a particular metal.

Question 29

Work function (Wo)

Answer 29

the minimum amount of energy needed to emit an electron from the surface of a metal.

Question 30

A metal will not eject e– if

Answer 30

• energy of photons < W0
• frequency of light < f0

Question 31

Force is stronger if

Answer 31

• Wo is bigger
• fo is bigger

Question 32

Absorption of photons

Answer 32

• e– can only absorb one photon
• photon energy, E = hf
• if 0 E < Wo, e– not ejected
• if 0 E = Wo, photon absorbed and photoelectron ejected with Ek = 0
• if 0 E > Wo, excess energy becomes Ek of photoelectron

Question 33

Comparing a brighter light to a dimmer light with the same f

Answer 33

• brighter light contains more photons, ∴ more photoelectrons ejected every second
• same f ∴ photons have same energy, ∴ each photoelectron has same Ek (from bright or dim light)

Question 34

Photoelectric effect theory

Explain why the number of electrons ejected per second
increases with the intensity of the incident radiation provided
the frequency is above the threshold frequency

Question 35

Photoelectric effect theory

Explain why if the frequency of the incident radiation is above
the threshold frequency, then increasing the frequency of the
radiation will increase the maximum kinetic energy of the
ejected electrons

Question 36

Emission spectra theory

Explain the source of atomic emission spectra (of discharge
tubes) and their unique relationship to each element

Relate the lines on the atomic spectrum to electron transitions
between energy levels