Topic 05: Waves and Particle Nature of Light

Question 1

Absorption spectrum

Answer 1

The frequencies at which a certain element absorbs photons at a higher rate as these frequencies correspond to the spacings between energy levels in the element’s atoms

Question 2

Amplitude

Answer 2

The maximum displacement of a vibrating particle or wave from its equilibrium position

Question 3

Angle of incidence

Answer 3

The angle at which a light ray hits a medium. Measured from a line perpendicular to the surface of the medium

Question 4

Angle of reflection

Answer 4

The angle at which a light ray reflects off a surface. Measured from a line perpendicular to the surface of the medium

Question 5

Angle of refraction

Answer 5

The angle at which light rays travel after transferring into a different refractive index material. Measured from a line perpendicular to the surface of the medium

Question 6

Antinode

Answer 6

The point on a stationary wave where the incoming and reflected wave are in phase forming a maximum point

Question 7

Coherence

Answer 7

Waves with the same frequency and constant phase difference

Question 8

Constructive interference

Answer 8

Interference when the two waves are in phase. If the two waves are both at their peak, the addition of the two peaks become large

Question 9

Critical angle

Answer 9

A lens that takes a parallel set of light rays and causes them to meet at a point

Question 10

De Broglie hypothesis

Answer 10

All particles have a wave-like nature and a particle-like nature. The wavelength of a particle is inversely proportional to the particle’s momentum

Question 11

De-excitation

Answer 11

The movement of an electron from a high-energy level to a lower energy level. This occurs in excited atoms over time and causes photons to be released

Question 12

Destructive interference

Answer 12

Interference when the two waves are in antiphase. When one wave is at a peak and one is at a trough, their addition results in a minimum point

Question 13

Diffraction

Answer 13

The spread of a wave as it passes through a gap or over an edge

Question 14

Displacement

Answer 14

The distance and direction that a vibrating particle or wave has travelled from its equilibrium position

Question 15

Diverging lens

Answer 15

A lens that takes a parallel set of light rays and causes them to travel away from each other and not meet

Question 16

Electronvolt

Answer 16

The kinetic energy gained by one electron that is accelerated through a potential difference of 1 volt. Equal to 1.6×10^(−16) J

Question 17

Emission spectrum

Answer 17

When a certain element’s atoms de-excite they move from one energy level to another with a specific energy gap between these levels. This creates a photon of that specific energy at it is the frequencies of these photos that make up the emission spectrum

Question 18

Excitation

Answer 18

The movement of an electron from a low energy level to a higher energy level. This occurs when an other electron or photon transfers energy to an orbital electron, causing it to move to a higher energy level

Question 19

Focal length

Answer 19

The distance from the centre of the lens to the focal point

Question 20

Focal point

Answer 20

The point at which rays of light passing through a lens converge (or appear to converge)

Question 21

Frequency

Answer 21

The number of complete oscillations of a wave (wave cycles) per second

Question 22

Fundamental frequency

Answer 22

The oscillations of an entire object forming the lowest possible frequency for that object. For a string fixed at both ends, this is where there is only a single antinode in the middle of the string

Question 23

Huygen’s principle

Answer 23

Every point on a wavefront can be treated as the point source of a secondary wavelet

Question 24

Ionisation

Answer 24

When an electron is removed from an atom, giving the atom a positive charge

Question 25

In antiphase

Answer 25

When the phase difference between two waves is 180 degrees or π radians

Question 26

In phase

Answer 26

When the phase difference between two waves is 0 degrees or 0 radians

Question 27

Intensity

Answer 27

The power transferred by a wave per unit area

Question 28

Lens power

Answer 28

The inverse of the focal length

Question 29

Longitudinal wave

Answer 29

A wave whose oscillations are parallel to the direction of propagation of the wave (e.g. sound waves)

Question 30

Magnification

Answer 30

The height of an object divided by the height of its image

Question 31

Node

Answer 31

The point on a stationary wave where the incoming and reflected wave are in antiphase, forming a minimum point

Question 32

One-to-one interaction

Answer 32

When one photon transfers all of its energy to a single electron in a photoelectric process

Question 33

Path difference

Answer 33

For two waves starting from different points and arriving at the same point, the path difference is the difference in the length travelled by each wave, measured in metres

Question 34

Period

Answer 34

The time taken for a wave to complete one full cycle

Question 35

Phase

Answer 35

If the full cycle of a wave (peak to peak) is represented on a circle with the first peak at 0° (0 radians), the trough at 180° (π radians) and the next peak at 360° (2π radians), the phase is where on that circle the wave is at a given point in space and time. Measured in radians or degrees

Question 36

Phase difference

Answer 36

The difference in phase if the phase of the two waves is determined at a single point in time, measured in radians or degrees. It can be seen as the amount by which one wave lags behind another

Question 37

Photoelectric effect

Answer 37

When light of a high enough energy shone on a metal surface causes electrons to be emitted. The electrons are given enough kinetic energy by the photons to overcome the attractive force of the ions in the metal

Question 38

Polarised wave

Answer 38

A wave whose oscillations have been restricted to the same plane

Question 39

Principal axis

Answer 39

A passing through the centre of the lens. Passing through the axis of the lens where it is thinnest

Question 40

Progressive wave

Answer 40

A wave that transfers energy from one point to another

Question 41

Pulse-echo technique

Answer 41

An ultrasound technique used for imaging of objects, notably in medical imaging. Short pulses of ultrasound are sent through a medium and their reflections recorded

Question 42

Real image

Answer 42

Where rays of light have actually converged to produce an image and can be projected onto a screen

Question 43

Refraction

Answer 43

When a wave changes speed when it crosses the boundary into a new medium

Question 44

Refractive index

Answer 44

A measure of how much the speed of light changes between two different media. If one media is a vacuum, then the absolute refractive index is found. For two different non-vacuum materials, the relative refractive index is found

Question 45

Snell’s law

Answer 45

The relative refractive index can be found from the ratio of the sines of the angles of incidence and refraction

Question 46

Snell’s law

Answer 46

The relative refractive index can be found from the ratio of the sines of the angles of incidence and refraction

Question 47

Stationary wave

Answer 47

A wave that stores energy instead of transferring it. A common example is a string fixed at both ends. They are formed by a wave propagating and being reflected so that it comes into superposition with itself

Question 48

Stationary wave

Answer 48

A wave that stores energy instead of transferring it. A common example is a string fixed at both ends. They are formed by a wave propagating and being reflected so that it comes into superposition with itself

Question 49

Superposition

Answer 49

When two waves meet at the same point in space, their displacements combine and the total displacement at that point becomes the sum of the individual displacements at that point. Also referred to as interference

Question 50

Threshold frequency

Answer 50

The minimum frequency of light needed to cause electrons to be emitted in the intensity

Question 51

Total internal reflection

Answer 51

When the angle of incidence is greater than the critical angle and the ray reflects at the surface and remains within the medium

Question 52

Transverse wave

Answer 52

A wave whose oscillations are perpendicular to the propagation of the wave (e.g. electromagnetic waves)

Question 53

Ultrasound

Answer 53

Sound waves with a frequency greater than 20 kHz

Question 54

Virtual image

Answer 54

When rays of light only appear to have converged and cannot be projected onto a screen

Question 55

Wavefront

Answer 55

The surface made up of all the points of the wave that are in phase with each other

Question 56

Wavelength

Answer 56

The distance between two identical points on a wave. Typically measured peak to peak or trough to trough

Question 57

Wave speed

Answer 57

The distance travelled by a wave per second. The product of the frequency and the wavelength. For an electromagnetic wave in a vacuum, this is always equal to c (3×10^8 ms^(-1))

Question 58

Work function

Answer 58

The minimum energy required to just liberate an electron from the surface of a metal