1 of 14 CT0pt 1 A ray of light is bent when it passes from water to air air water This is an example of A Huygen s Principle C The superposition principle Answer Snell s Law B Snell s Law D The lens equation 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 2009 2 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 I II III 25 35 40 25 A nI nIII B nI nIII 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 C nI nIII D Impossible to tell 12 9 2009 Phys1120 Concept Tests 12 9 2009 3 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 C bent toward the thick end B undeviated goes straight thru air n 1 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 A B C 12 9 2009 Phys1120 Concept Tests 12 9 2009 A B C D 4 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 air n 1 glass n 1 5 air glass 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 n n sin g w 0 c 1 n sin 90 w n w n g c sin 12 9 2009 Phys1120 Concept Tests 12 9 2009 5 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 C smaller f 20cm but still positive B greater f 20 cm 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 depends on the change in the index of refraction n Bigger change in n means bigger change in angle 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 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 f rays in 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 Eye A A single point of light surrounded by blackness 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 2009 6 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 2 screen lens mask 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 12 9 2009 Phys1120 Concept Tests 12 9 2009 7 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 object A B C image lens 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 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 …