Particles and Waves Part 2 (inverse square law, wave particle duality, interference, refraction) Flashcards
What characteristic of waves is shown in this diagram?
Interference
What is the definition of absolute refractive index of a medium (or material)?
Absolute refractive index is the ratio of speed of light in a vacuum to speed of light in the medium.
Explain what is shown in this picture.
This is destructive interference.
Two waves meet at a point exactly out-of-phase (crest meets trough, and trough meets crest) to form a wave of reduced amplitude.
(if both waves are the same amplitude then the new amplitude will be zero)
Waves from two coherent sources arrive at points P0 and P1.
P0 is the same distance from both sources.
What name is given to point P0 ?
The central maximum.
(m = 0)
When light passes from a material into one with a lower refractive index (e.g. glass to air), what happens to its speed?
When light passes from a material into one with a lower refractive index (e.g. glass to air), its speed increases.
The diagram shows refraction of different colours (frequencies).
What conclusion can be drawn about the relationship between frequency and refractive index?
Violet light has a higher frequency than red.
Violet light is refracted by a greater angle than red.
The higher the frequency, the greater the refractive index.
What is the unit for refractive index (n)?
There are no units for refractive index.
It is purely a ratio (should be a number >1).
A ray of light, inside a block of glass, hits the surface of the glass.
The angle is greater than the critical angle.
What will happen to the ray of light?
The ray of light will be totally internally reflected.
What does the symbol f0 represent?
f0 represents the threshold frequency - the minimum frequency of radiation required to eject an electron from the surface of a metal.
Waves from two coherent sources meet at point P0, perfectly in phase.
What name is given to point P0 ?
Point P0 is a maximum.
What is the definition of critical angle?
Critical angle is the angle of incidence that results in an angle of refraction of 90° to the normal.
When light passes from a material into one with a lower refractive index (e.g. glass to air), what happens to its frequency?
When light passes from a material into one with a lower refractive index (e.g. glass to air), its frequency remains constant.
When light passes from air (or a vacuum) into a material of a greater refractive index, what happens to its frequency?
When light passes from air (or a vacuum) into a material of a greater refractive index, its frequency remains constant.
What is the unit for wavelength?
The unit for wavelength is metres (m).
A ray of white light is refracted by a prism.
Describe the pattern produced.
A spectrum would be produced.
Red is refracted the least, violet refracted the most.
What characteristic of waves is shown in this diagram?
Reflection
List the different characteristics (or behaviours’) that all waves display
(four possible answers)
- diffraction
- reflection
- refraction
- interference
What is meant by waves which are coherent?
Coherent means that waves have the same frequency, wavelength and velocity, and have a constant phase relationship.
The examples shown are both of coherent waves.
In the diagram, a ray of red light undergoes refraction as it enters a glass block.
Which angles should be used to calculate the refractive index of the glass?
The angles B (air) and E (glass) should be used.
In an experiment to demonstrate the photoelectric effect, a gold leaf electroscope is negatively charged, and an ultraviolet lamp is directed at a steel cap.
The electroscope does not discharge.
Suggest a change that could be made to the experiment which would cause the electroscope to discharge.
The metal cap of the electroscope could be changed to one with a lower work function than steel (for example, zinc).
Name the three quantities shown in this formula, and give the unit for each one.
I is irradiance (in W m-2)
P is power (in W)
A is area (in m2)
A ray of white light is incident on a diffraction grating.
Describe the pattern that would be produced.
There are several maxima observed.
There is a white central maximum.
There are spectra either side of the central maximum.
In each spectrum, violet is diffracted the least, red is diffracted the most.
In an experiment to demonstrate the photoelectric effect, a gold leaf electroscope is negatively charged, and an ultraviolet lamp is directed at the metal. The electroscope discharges (the gold leaf slowly falls).
A UV lamp with the same frequency, but greater intensity, is now used.
What difference would be observed in the experiment?
Explain your answer.
The gold leaf (in the electroscope) would fall faster.
A UV lamp of greater intensity will emit more photons per second, meaning more electrons per second are ejected from the metal.
Waves from two coherent sources arrive at point P0.
Point P0 is exactly the same distance from sources S1 and S2.
Explain what is happening at P0.
Point P0 is a maximum.
Constructive interference is occurring at P0 because path difference = zero.
The waves are meeting at P0 in phase.
Waves from two coherent sources arrive at point P1.
The distance from S1 to P1 is one whole wavelength less than the distance from S2 to P1.
Explain what is happening at P1.
Point P1 is a maximum.
Constructive interference is occurring at P1 because path difference = λ.
The waves from S1 and S2 meet in phase.
What characteristic of waves is shown in this diagram?
Refraction
The relationship between irradiance and distance is an example of an inverse square law.
What is meant by an ‘inverse square law’ - in this context?
An inverse square law, in this context, means that if the distance is multiplied by 2, the irradiance is divided by 4 (2 squared).
If the distance is multiplied by 10, the irradiance is divided by 100 (10 squared) - and so on.
Explain what is shown in this picture.
This is constructive interference.
Two waves meet at a point exactly in phase (peak meets peak, and trough meets trough) to form a wave of increased amplitude.
Define all symbols in the formulae shown.
n = refractive index
ϴ = angle (in air or in a material)
λ = wavelength (in air or in a material)
v = speed of light (in air or in a material)
In an experiment to demonstrate the photoelectric effect, a gold leaf electroscope is negatively charged, and a red laser is directed at the metal. The electroscope does not discharge.
When the experiment is repeated with a violet laser, the electroscope does discharge.
Explain why this happens.
Violet light has a shorter wavelength / higher frequency than red light.
The photons from the violet laser will have a greater energy than red.
The energy of the photons is given by E = hf.
What characteristic of waves is shown in this diagram?
Diffraction
