waves and particle nature of light

Question 1

Amplitude

Answer 1

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

Question 2

Angle of incidence

Answer 2

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

Question 3

Angle of reflection

Answer 3

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

Question 4

Angle of refraction

Answer 4

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 5

Antinode

Answer 5

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

Question 6

Coherence

Answer 6

Waves with the same frequency and constant phase difference.

Question 7

Constructive interference

Answer 7

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

Question 8

Converging lens

Answer 8

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

Question 9

Critical angle

Answer 9

The angle of incidence when the angle of refraction is exactly 90 degrees It is when
the refracted ray travels along the boundary line.

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 1.6x10-16 J.

Question 17

Excitation

Answer 17

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

Question 18

Focal length

Answer 18

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

Question 19

Focal point

Answer 19

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

Question 20

Frequency

Answer 20

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

Question 21

Fundamental frequency

Answer 21

The oscillation 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 22

Huygen’s principle

Answer 22

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

Question 23

Ionisation

Answer 23

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

Question 24

Anti-phase

Answer 24

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

Question 25

In-phase

Answer 25

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

Question 26

Intensity

Answer 26

The power transferred by a wave per unit area.

Question 27

Lens power

Answer 27

The inverse of the focal length.

Question 28

Longitudinal waves

Answer 28

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

Question 29

Node

Answer 29

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

Question 30

One to one interaction

Answer 30

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

Question 31

Path difference

Answer 31

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 32

Period

Answer 32

The time taken for a wave to complete one full cycle.

Question 33

Phase difference

Answer 33

The difference in phase if the phase of 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 34

Photoelectric effect

Answer 34

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 35

Polarised wave

Answer 35

A wave whose oscillations have been restricted to the same plane

Question 36

Principle axis

Answer 36

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

Question 37

Progressive wave

Answer 37

A wave that transfers energy from one point to another.

Question 38

Progressive wave

Answer 38

A wave that transfers energy from one point to another.

Question 39

Pulse echo technique

Answer 39

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 40

Real image

Answer 40

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

Question 41

Refraction

Answer 41

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

Question 42

Refractive index

Answer 42

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 43

Snell's law

Answer 43

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

Question 44

Stationary wave

Answer 44

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 45

Superposition

Answer 45

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 46

Threshold frequency

Answer 46

The minimum frequency of light needed to cause electrons to be emitted in the photoelectric effect regardless of the intensity.

Question 47

Total internal reflection

Answer 47

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

Question 48

Transverse wave

Answer 48

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

Question 49

Ultrasound

Answer 49

Sound waves with a frequency greater than 20 kHz.

Question 50

Virtual image

Answer 50

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

Question 51

wavefront

Answer 51

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

Question 52

Wavelength

Answer 52

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

Question 53

Wave speed

Answer 53

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 (3x10^8 m/s)