PHY504 Midyear Practice Exam Questions Please keep in mind that you will have 3 hours to complete the January exam, and that it will have 15 questions based on everything we have learned throughout the Geometric Optics unit. There will also be a single question asking you to explain the optics behind a device (similar to what you were asked to do for your project). Background information will be provided about the device to assist you. Finally, please be sure that you have a geometry set as well as a non-graphing SCIENTIFIC calculator and writing implements for your January exam (as none will be provided). These sample questions are provided to help you focus your studies and test yourself. Completing these practice questions is not sufficient preparation for the exam!!

1. Which of the following light phenomena accounts for the colours in a rainbow?   A) Diffraction C) Dispersion B) Diffusion D) Reflection

2. The following diagram depicts a side-view mirror of a car. What type of mirror would produce this effect?   A) Plane C) Converging B) Convex D) Concave

3. Julie came back from the ophthalmologist who told her she is suffering from hyperopia, a condition in which images are formed behind the retina in the eye.

3. Which one of the following correction lenses would help Julie?

4. Haran is manipulating a concave mirror that has a focal length of 10.0 cm. His physics teacher tells him that the difference between do and di is 15.0 cm and that the image is larger than the object and has a negative magnification. Where should Haran place the object to obtain the desired image?   A) do = 15.0 cm and di = 30.0 cm B) do = 30.0 cm and di = 15.0 cm C) do = 5.0 cm and di = -10.0 cm D) do = 10.0 cm and di = -5.0 cm

4. A pinhole camera was set up to view a 5.0 cm matchstick. The distance to the matchstick was twice the depth of the camera. What was the height of the image on the screen?   A) 50.0 cm B) 10.0 cm C) 5.0 cm D) 2.5 cm

6. Which of the following explains why this page (screen) is visible?   A) It is incandescent. B) It emits light. C) It refracts light. D) It reflects light.

7. The four diagrams below show a single ray of light reflected off surfaces of different shapes. All the surfaces are covered with polished metal. Which diagram does not respect the law of reflection?   A) Diagram 1 C) Diagram 3 B) Diagram 2 D) Diagram 4

8. Which illustrations correspond to each of the phenomena listed below? Write the letter of the illustration on the corresponding numbered line of the phenomenon. Phenomena 1. Specular reflection 2. Diffuse reflection 3. Refraction B A B E A C C D E

9. The converging lens of a slide projector has a focal length of 10 9. The converging lens of a slide projector has a focal length of 10.0 cm. This lens is located 4.10 m from a vertical screen. A slide is placed in the projector and the lens is adjusted to produce a clear image on the screen. What is the distance between the lens and the slide?   A) 2.50  10-1 cm B) 1.00  101 cm C) 1.03  101 cm D) 2.38  101 cm

10. A lens system is made up of two lenses cemented together 10. A lens system is made up of two lenses cemented together. The focal lengths of these lenses are 50 cm and -40 cm. What is the optical power of this lens system?   A) -0.50 dioptre B) 0.10 dioptre C) 4.5 dioptres D) 10 dioptres

11. The following diagram shows a concave mirror 11. The following diagram shows a concave mirror. To produce an upright image, where should the object be placed?   A) Point A C) Point C B) Point B D) Point D

What is the purpose of the umbrella-shaped screens? 12. A professional photographer uses umbrella-shaped screens made of aluminum foil and a white screen set up behind the object to be photographed. What is the purpose of the umbrella-shaped screens?   A) They concentrate the light emitted by the camera onto the object to be photographed. B) They reflect the light from the projection lights onto the object so that it is illuminated from all sides. C) They obtain specular reflection of the light emitted by the object. D) They concentrate the reflected light on the photographic equipment.

13. The sextant illustrated below has been set to view the image of only one of the four stars shown in the diagram. Which star can be observed?   A) Star 1 C) Star 3 B) Star 2 D) Star 4

14. A person is walking towards a plane mirror at a speed of 1 m/s 14. A person is walking towards a plane mirror at a speed of 1 m/s. At the same time, the image of this person formed by the mirror is also moving. Which of the following statements is TRUE?   A) The image is approaching the person at a speed of 2 m/s. B) person at a speed of 1 m/s. C) The image is moving from the D)

How will the area of the penumbra on the screen change? A) 15. In a laboratory experiment, the following set up was established. The obstacle was then moved closer to the screen, while the light source remained in the same position. How will the area of the penumbra on the screen change?   A) The area of the penumbra on the screen will decrease. B) the screen will remain the same. C) the screen will increase. D) the screen will first increase then decrease.

16. The following diagram shows a light ray striking a concave spherical mirror.

16. Which of the following diagrams best represents the path of the light ray reflected by the mirror? A) C) B) D)

Symbols:  Represents the driver’s eye.  Represents the students. 17. Using three mirrors, a school bus driver is able to view students leaving the bus. One plane mirror and two convex mirrors are shown in the following diagram. There are 5 students surrounding the bus. Symbols:  Represents the driver’s eye.  Represents the students.  C Represents the centre of curvature. Construct field of vision diagram, identifying the student(s) the driver CANNOT see in the mirrors.

17.

18. During an experiment on optical power and lens combinations, Sophie came up with a calculated optical power of 0 dioptres for a set of two lenses. Hassan, her lab partner, concluded that the result could not be possible. Who is right? How would you justify your answer from an optics point of view? Support your answer, in a short written justification, using all three of the following concepts:  optical power  focal length  magnification Optical power is additive so a negative and positive lens could be used to cancel each other out (e.g. 2δ & -2δ). Focal length is not additive and should not be used to determine the combined effect of two lenses. An optical power of zero corresponds to an infinite focal length. See, www.colorado.edu/physics/phys1230/phys1230_fa01/topic27.html

19. Nadia is conducting a physics experiment using a converging lens on an optical bench. The professor has said that the object must be 64.0 cm from the screen. Nadia is told that the focal length of the lens is 12.0 cm How far from the object must Nadia place the lens to obtain a clear and larger image on the screen? Show all your work.

Potentially relevant equations. 19. F = 0.12 m di + do = 0.64 m do = ? Potentially relevant equations.      

19. 𝑑 𝑜 𝑑− 𝑑 𝑜 =𝑓 𝑑− 𝑑 𝑜 + 𝑑 𝑜 =𝑓𝑑 𝑑 𝑜 2 − 0.64 𝑚 𝑑 𝑜 + 0.64 𝑚 0.12 𝑚 =0 𝑑 𝑜 must be between f & 2f, Table 2, p. 114. 𝑑 𝑜 =0.16 𝑚

20. A glass prism with a refractive index of 1 20. A glass prism with a refractive index of 1.5 is used with a light source in the form of an arrow. The light enters the perpendicular prism through the nearest side. Θc = arcsin( 1.0 / 1.5) = 41.8° 45° is greater than Θc, so there is total internal reflection Show the orientation of the arrow as the beam exits the prism. Show all lines.

21. Optical fibers are now widely used in telecommunications 21. Optical fibers are now widely used in telecommunications. Sound waves are transformed into light waves which are then transmitted by optical fibers.   Which light phenomenon makes it possible to use optical fibers for this purpose? Total internal reflection is used so that the light will reflect internally along the length of the optical fiber without losing light via transmission through the walls of the fiber. The outer surface of the fiber is coated with a material that has a lower index of refraction than the core of the fiber.

22. The diagram on the right represents a box through which light is to pass from opening A to opening B. Several small plane mirrors are available. Θi = 45° Θi = 45° Θi = 45° How would you place the mirrors in the box so that the light passes from A to B?   On the diagram in the answer booklet, draw lines to indicate the position of the mirrors and the path of the rays; also specify the values of the angles of incidence. All elements must be included for marks to be allotted.

Calculate the angle between the two refracted rays. 23. The index of refraction for a certain kind of glass is 1.67 for blue light and 1.61 for red light. A beam containing these two colours hits the glass with an angle of incidence of 45°. (Diagram is not drawn to scale.) Θi = 45°, nr = 1.61, Nb = 1.67         Calculate the angle between the two refracted rays.

24. Draw a diagram in the Answer Booklet to show where an object must be placed in order for it to be illuminated by the two rays I1 and I2. Draw the reflected rays.

25. The diagram below represents an object and a converging lens. Knowing the focal point of the lens, state two characteristics of the image formed by this system. Since the focal point is in front of the lens, the lens is diverging or negative lens. It will produce a real, inverted image smaller than the object, p.114.

26. For each of the following diagrams, identify the defect in the eye, if there is one, and indicate the kind of lens needed to correct the defect and restore normal vision. Defect: ____________________ Type of Lens: ___________________________ Hyperopia Diagram 1 Converging Lens Diagram 2 Defect: ____________________ Type of Lens: ___________________________ Emmetropia None Diagram 3 Defect: ____________________ Type of Lens: ___________________________ Myopia Diverging Lens

Potentially relevant equations. 27. A 2.0 cm tall object is located 4.0 cm from a converging lens that has a focal length of 12 cm. What is the magnification of the image?   Potentially relevant equations.         Check Table 2, p. 114

28. A light ray travelling in air enters an unknown substance at an angle of incidence of 40.0°. The angle of refraction is 25.4°. Determine the value of the critical angle for this unknown substance. Show all your work. Θi = 40.0° θR = 25.4° n1 = 1 n2 = ? 40° 25.4° 𝑛 2 = 𝑛 1 sin θ 𝑖 sin θ 𝑅 = 1 sin 40° sin 25.4° =1.50 Θc = arcsin( 1 / 1.50) = 41.8°

29. Illustrated below is the inside of a closed box 29. Illustrated below is the inside of a closed box. There is one hole through which a light ray enters as shown. nair = 1.0 nprism = 1.5 Where should a second hole be placed in order for the light ray to exit the box? You must show the complete path of the light ray to find your answer. Show all your work.

29. nair = 1.0 nprism = 1.5 30° 30° θ 𝑡 = sin −1 1 sin 30° 1.5 =19.5° 70.5° 19.5° θ 𝑡 = sin −1 1 sin 30° 1.5 =19.5°

29. nair = 1.0 nprism = 1.5 Θc = arcsin( 1 / 1.50) = 41.8° 70.5° 40.5° 49.5° 76.9° θ 𝑡 = sin −1 1.5 sin 40.5° 1 =76.9°

30. A candle, AB, is placed in front of a plane mirror 30. A candle, AB, is placed in front of a plane mirror. On the diagram in your Answer Booklet, locate and draw the image of the candle. Using the image of the candle, then draw light rays that show how the eye sees point B on the candle in the mirror. Show all your work.