1 of 14 CT0pt-1 A ray of light is bent when it passes from water to air. airwaterThis is an example of: A) Huygen's Principle B) Snell's Law C) The superposition principle D) The lens equation Answer: Snell's Law CT0pt -2. A man is looking in a mirror and he sees his face just filling the mirror. The man now moves back, away from the mirror, watching his reflection. As he moves back, he sees the image of his face.. A) continues to just fill the mirror B) becomes smaller than the frame of the mirror C) become larger than the frame of the mirror. Answer: From the man's point of view, his image always just fills the mirror. From his point of view, both the mirror frame and the (virtual) image get smaller by the same amount as he moves away. If he doubles the distance L to the mirror, he is also doubling the distance 2L to his image. 12/9/2009 Phys1120 Concept Tests 12/9/20092 of 14 Man Virtual Image CT0pt -3 A ray of light passes through 3 regions labeled I, II, and III, as shown. How do the indices of refraction of regions I and III compare? A) nI > nIII B) nI < nIII C) nI = nIII D) Impossible to tell. Answer: nI < nIII. In refraction, the ray always gets bent toward the normal in the medium with the larger n. The presence of medium II in between I and III has no effect on the final ray's angle. If you shrink region II to a smaller slab, none of the angles change. So you can shrink II down to zero thickness and ignore it. III III25°35°25°40°12/9/2009 Phys1120 Concept Tests 12/9/20093 of 14 CT0pt -4. A ray of light passes thru a sheet of glass which is thick at the bottom and thin at the top. Which way is the ray traveling after it has passed through the glass? A) bent toward the thin end B) undeviated (goes straight thru) C) bent toward the thick end A)B)air, n=1C)glass, n=1.5 Answer: the ray is bent away from the thin end, toward the thick end. On entering the glass, the ray is bent toward the normal (since the ray is always bent toward the normal in the higher-n material). On exiting, it is bent away from the normal. Both refractions, bend the ray away from the thicker end. 12/9/2009 Phys1120 Concept Tests 12/9/20094 of 14 CT0pt -5. A light ray passes from air to glass (smaller n to larger n) as shown. Which way does the ray travel in the glass? A)air, n=1B)C)glass, n=1.5D) Answer: C CT0pt -6. A light ray inside glass is totally internally reflected from an air-glass interface as shown. The air surrounding the glass is replaced with water. With the same light ray in the glass, the total internal reflection will now... A) definitely not occur. B) definitely occur. C) not enough information to know Answer: not enough information to know. Whether total internal reflection will occur depends on the angle of incidence AND on the relative indices of refraction of the glass and water. The critical angle is given by: 0gcw1wcgnsin nsin90 nnsinn−θ= =⎛⎞θ=⎜⎟⎜⎟⎝⎠w airglass12/9/2009 Phys1120 Concept Tests 12/9/20095 of 14 CT0pt -7. A converging lens has a focal length f = 20cm when it is in air. The lens is made of glass with index of refraction nglass = 1.6. When the lens is placed in water (nwater = 1.33), the focal length of the lens is.. .. A) Unchanged. B) greater, f > 20 cm. C) smaller, f < 20cm, but still positive D) negative. Answer: greater, f > 20cm. The rays of light are bent when they pass from the medium (air or water) into the glass according to Snell's law. The amount of bending (the change in the angle, ∆θ) depends on the change in the index of refraction, ∆n. Bigger change in n means bigger change in angle, ∆θ, that is, more bending. If the lens is immersed in a fluid with the same n as the glass, then there is no refraction: ∆n = 0, ∆θ = 0. When the lens is in air the change in n is ∆n = 1.6 – 1 = 0.6. When the lens is in water, the change in n is ∆n = 1.6 – 1.33 = 0.27. Smaller ∆n in the water means less bending, a longer focal length f. rays in water (less bending of ray, longer fraysin air CT0pt -8. A bundle of parallel rays approaches the eye and some of the rays enter the eye's pupil, as shown below. No other rays enter the eye. What does the eye see? A) A single point of light, surrounded by blackness. Eye B) A uniformly illuminated wall of light, like a white wall. C) Many scattered points of light, like stars in the night sky. D) None of these 12/9/2009 Phys1120 Concept Tests 12/9/20096 of 14 Answer: A single point of light, surrounded by blackness. A point source at infinity makes a parallel bundle of rays. The lens of the eye focuses these rays onto a point on the retina, and the brain perceives a point of light. CT0pt -9 Two point sources of light are imaged onto a screen by a converging lens as shown. The images are labeled 1 and 2. A mask is used to cover up the left half of the lens, as shown. What happens to the images on the screen when the mask is inserted over the left half the lens? 1 A) Image 1 vanishes B) Image 2 vanishes C) Something else happens. Answer: Something else happens. Both images dim somewhat but neither disappears. Rays from each source cover the entire lens. When half the lens is covered, half the rays from each source are blocked, but the other half get through, producing a dimmed image. 2screenlensmask12/9/2009 Phys1120 Concept Tests 12/9/20097 of 14 CT0pt -10 A converging lens focuses the light from a nearby point source onto an image, as shown. The "focal point" of a lens is the point on the optic axis, one focal length f from the lens. Where is the focal point of this lens? A) between the lens and the image B) at the image C) further from the lens than the image. Answer: the focal point is between the image and the lens. The focal point is where parallel rays (along the optic axis) would focus. A ray hitting the edge of the lens will be bent by same angle α , regardless of the incoming angle. So when the object moves (from infinity) toward the lens, the image moves away from the lens, but the focal point remains stationary by definition. objectimageA) B) C)lensα α, same angle12/9/2009 Phys1120 Concept Tests 12/9/20098 of 14 CT0pt -11. An object is placed is placed near a diverging lens, but the object is further from the lens than the absolute value of the focal length of the lens. The image formed is.. A) Real B)
View Full Document
Unlocking...