SPH4U - Physics for University
Test 5 - Unit 4
Waves
Multiple Choice - ***Circle one choice for each question.***
1. (10 points) [K, T]
(a) Which of the following is not a category used to describe waves?
A. Transverse
B. Mechanical
C. Longitudinal
D. Energetic
(b) Electromagnetic waves are a special category of waves that do not require .
A. energy to propagate
B. a medium to propagate
C. a vacuum to propagate
D. a slit for diffraction
(c) The refractive index is a ratio that measures .
A. The change in velocity of a wave between mediums
B. The angle at which a wave will bend
C. The wavelength of an incidence wave
D. The velocity of light in a vacuum
(d) Perfect is achieved when two waves are out of phase with each other (peak to trough).
A. constructive interference
B. constructive diffraction
C. destructive interference
D. destructive refraction
(e) The photoelectric effect depends on which wave characteristic?
A. Frequency.
B. Amplitude.
C. Velocity.
D. Intensity.
(f) Which of the following processes is achieved bypassing light through a filter?
A. Scattering of white light.
B. Polarization.
C. Thin film interference.
D. Reflection.
(g) π shift results from which of the following scenarios?
A. Refraction in a medium that decreases wave speed.
B. Refraction in a medium that increases wave speed.
C. Reflection off a medium that would have increased wave speed.
D. Reflection off a medium that would have decreased waves speed.
(h) Which of the following theories explains why light can produce an interference pattern in a singleslit exper- iment.
A. Einsteins’ theory of wave/particle duality .
B. Newtons’ theory of corpuscles.
C. Huygens’ theory of wavelets.
D. Snells’ law.
(i) Which of the following is NOT a method of polarization?
A. Scattering
B. Diffraction
C. Double refraction
D. Reflection
(j) is a product of thin film interference
A. Iridescence
B. White light scattering
C. Single slit diffraction
D. Polarization
Short Answers - ***Give complete answers, SHOW ALL OF YOUR WORK, don’t forget to use GRASP - Given, Required, Analysis, Solve, Paraphrase.***
2. (10 points) [A, T] In water where light can not pass through, dolphins will resort to echolocation as a sense rather than eyesight.
(a) In air where nair = 1.00, the speed of sound is measured as 380m/s. If nwater is 1.33, calculate the new speed of sound. (3 pts)
(b) The dolphin uses its’ echolocation to judge the distance of a fish nearby. A wave is sent out and received again in 0.008s, calculate the distance of the fish from the dolphin (4 pts)
(c) The frequency of the wave emitted by the dolphin is at 255khz, what is the wavelength? (3 pts)
3. (10 points) [C,A, T] A wave passes from air into ethyl alcohol (n = 1.36) at an angle of incidence 37。.
(a) Using the template provided below, draw the expected refraction of the wave. (Include the following infor- mation: the normal line, and wave fronts to represent the wavelength) (2 pts)
(b) If the initial wavelength of the wave is 940nm, calculate both the angle of refraction and the new wavelength.
(4 pts)
(c) In this instance, the refraction is not perfect and there is partial reflection.
i) In the space below, calculate and justify the angle of reflection. (2 pts)
ii) Using the information given within this question, what do we know about the phase of thereflected wave?
(2 pts)
4. (15 points) [K, A] When light passes through a narrow opening or around an obstacle, we often see diffraction.
(a) A wave of light with λ 0.82cm passes through an opening with an aperture of 0.6cm. Will there be noticeable diffraction? (2 pts)
(b) A second slit is introduced and a pattern emerges containing lines of constructive and destructive interference. In the space below, explain how the following pattern is generated: (2 pts)
Constructive interference
Destructive interference
(c) If the distance between the two slits is 0.045m, determine the angle θ of a point where both waves meet at the 3rd anti-nodal line. (4 pts)
(d) Calculate the difference in path-length between the two waves at the 3rd anti-nodal line. (2 pts)
5. (15 points) [K, C] In the late 1800s/early 1900s, scientists witnessed a new phenomenon known as the photoelec- tric effect. This would lead to the theory of wave-particle duality.
Scientist Heinrich Hertz was the first to witness the photoelectric effect - he found, when experimenting with UV rays, that when shone on a metal sheet, electrons would begin to escape.
(a) With the understanding of classical wave theory, explain what Hertz was expecting to see in his experiment with amplitude of waves? (Hint: Energy is directly proportional to amplitude) (4 pts)
(b) To his surprise Hertz found amplitude would not trigger the photoelectric effect. He found however, that a variation in wavelength would. This would be built upon later by Einstein who gave his relationship as E = hf.
i) Explain why varying wavelength would trigger the photoelectric effect. (Answer using the relationship between wavelength and frequency). (2 pts)
ii) Explain how waves above a threshold frequency cause the electrons to escape. (4 pts)
(c) It was determined through the electron double slit experiment that quantum matter (like electrons and pho- tons) had properties of both waves and particles. A limitation in measuring quantum matter is the observer effect - in the space below, explain the observer effect. (5 pts)
6. (10 points) [K, T] Some sunglasses allow for reduction in intensity of light by using a polarizing filter.
(a) If light arrives at the glasses with an intensity of 145cd, at an angle of 20。. Calculate the new intensity through polarised glasses. (Note: the SI unit for light intensity is Candela (cd)) (2 pts)
(b) An analyser is used to test light for polarization - explain how an analyser is used. (3 pts)
(c) In the space below, explain how light reflecting off a new medium can be polarised. (3 pts)
(d) Light travels through glass (nglass = 1.52) andreflects off of water (nwater = 1.33), calculate the angle needed for perfect polarization (also known as Brewster’s angle). (2 pts)
7. (10 points) [K, A] When passing light waves through a single slit, it was found that an interference pattern is still generated.
(a) The single slit interference was explained by Huygens and his theory of wavelets. In the space below, explain how the wavelet theory can create a single wave interference pattern. (4 pts)
(b) A light source has a wavelength of 550nm, and passes through a slit with an aperture of 5μm. Calculate the thickness of the first order bright fringe in degrees. (3 pts).
(c) Calculate the distance (△y) between the 1st and 2nd order bright fringes if the screen that the pattern is projected onto is 1.2cm away. (3 pts).
8. (10 points) [C,A, T] Oil slicks are an example a phenomenon known as thin film interference.
(a) Explain how partial reflection and partial refraction lead to thin film interference. (4 pts)
(b) The thickness of the film dictates whether light waves will interfere in a constructive or destructive way. Explain how this is the case. (3 pts)
(c) A wave of light with wavelength 484nm enters from the gasoline medium (ngasoline = 1.40) into a water medium (nwater = 1.33). Calculate the new wavelength. (3 pts)
(d) Will constructive interference happen at whole or partial integers of the wavelength in this example? Justify your answer. (2 pts)
(e) What are the three smallest thicknesses of water that will results in constructive interference? (3 pts).
9. (10 points) [A, T] A general rule states that the resolution of an interference pattern increases with the number of slits used. This leads to the use of a diffraction grating in most laboratory settings.
(a) A wave of light is passed through a diffraction grating (300lines/cm) with a 3rd order maxima at an angle of 23。. Calculate the wavelength. (3 pts)
(b) Calculate the frequency of the wave in part a. (Note: assume the light is travelling in air with a velocity of c). (2 pts)
(c) When white light is used in a diffraction grating, we get white light scattering into a rainbow at each maxima.
Explain how a diffraction grating creates the rainbow spectrum pattern seen in the image below. (3 pts)
(d) Explain why there is no rainbow scattering at the 0 order maxima. (2 pts)