Q&A Hero

Q: Yellow light is viewed by reflection from a thin vertical soap film. Let be the wavelength of the light within the film. Why is there a large dark space at the top of the film?A) no light is transmitted through this part of the filmB) the film thickness there is /4C) the light reflected from exactly one of the two surfaces undergoes a 180ï‚°phase changeD) the film is too thick in this region for thin film formulas to applyE) the reflected light is in the infrared

Q: Red light is viewed through a thin vertical soap film. At the third dark area shown, the thickness of the film, in terms of the wavelength within the film, is:

Q: A soap film is illuminated by white light normal to its surface. The index of refraction of the film is 1.50. Wavelengths of 480 nm and 800 nm and no wavelengths between are intensified in the reflected beam. The thickness of the film is:A) 1.5 x10-5cmB) 2.4 x10-5cmC) 3.6 x10-5cmD) 4.0 x10-5cmE) 6.0 x10-5cm

Q: The three factors that determine the interference of reflected waves from a thin film are: A) incoming wavelength, speed of light in vacuum, thickness of the film B) shifts in wavelength on reflection, path length difference, index of refraction of the film C) incoming wavelength, index of refraction of the external medium, index of refraction of the film D) shifts in wavelength on reflection, index of refraction of the film, speed of light in vacuum E) path length difference, thickness of the film, index of refraction of the film

Q: A glass (n= 1.6) lens is coated with a thin film (n= 1.3) to reduce reflection of certain incident light. If is the wavelength of the light in the film, the least film thickness is:

Q: A lens with a refractive index of 1.5 is coated with a material of refractive index 1.2 in order to minimize reflection. If denotes the wavelength of the incident light in air, what is the thinnest possible such coating?

Q: Three experiments involving a thin film (in air) are shown. If tdenotes the film thickness and denotes the wavelength of the light in the film, which experiments will produce constructive interference as seen by the observer? A) I only B) II only C) III only D) I and III only E) II and III only

Q: Monochromatic light, at normal incidence, strikes a thin film in air. If denotes the wavelength in the film, what is the thinnest film in which the reflected light will be a maximum?

Q: Binoculars and microscopes are frequently made with coated optics by adding a thin layer of transparent material to the lens surface as shown, in order to improve light transmission. One wants: A) constructive interference between waves 1 and 2 B) destructive interference between waves 3 and 4 C) constructive interference between waves 3 and 4 D) the coating to be more transparent than the lens E) the speed of light in the coating to be less than that in the lens

Q: A light wave with an electric field amplitude of 2E0and a phase constant of zero is to be combined with one of the following waves. Which of these combinations produces the least intensity?A) wave A has an amplitude of E0and a phase constant of zeroB) wave B has an amplitude of E0and a phase constant of C) wave C has an amplitude of 2E0and a phase constant of zeroD) wave D has an amplitude of 2E0and a phase constant of E) wave E has an amplitude of 3E0and a phase constant of

Q: A light wave with an electric field amplitude of E0and a phase constant of zero is to be combined with one of the following waves. Which of these combinations produces the greatest intensity?A) wave A has an amplitude of E0and a phase constant of zeroB) wave B has an amplitude of E0and a phase constant of C) wave C has an amplitude of 2E0and a phase constant of zeroD) wave D has an amplitude of 2E0and a phase constant of E) wave E has an amplitude of 3E0and a phase constant of

Q: To obtain an observable double-slit fringe pattern: A) the light must be incident normally on the slits B) the light must be monochromatic C) the light must consist of plane waves D) the light must be coherent E) the screen must be far away from the slits

Q: If two light waves are coherent: A) their amplitudes are the same B) their frequencies are the same C) their wavelengths are the same D) their phase difference is constant E) the difference in their frequencies is constant

Q: In a Young's experiment, it is essential that the two beams: A) have exactly equal intensity B) be exactly parallel C) travel equal distances D) come originally from the same source E) be composed of a broad band of frequencies

Q: One of the two slits in a Young's experiment is painted over so that it transmits only one-half the intensity of the other slit. As a result: A) the fringe system disappears B) the bright fringes get brighter and the dark ones get darker C) the fringes just get dimmer D) the dark fringes just get brighter E) the dark fringes get brighter and the bright ones get darker

Q: In a Young's double-slit experiment, a thin sheet of mica is placed over one of the two slits. As a result, the center of the fringe pattern (on the screen) shifts so that the center is now occupied by what was the30thdark band. The wavelength of the light in this experiment is 480 nm and the index of the mica is 1.60. The mica thickness is: A) 0.009 mm B) 0.012 mm C) 0.014 mm D) 0.024 mm E) 0.062 mm

Q: Light from a small region of an ordinary incandescent bulb is passed through a yellow filter and then serves as the source for a Young's double-slit experiment. Which of the following changes would cause the interference pattern to be more closely spaced? A) Use slits that are closer together B) Use a light source of lower intensity C) Use a light source of higher intensity D) Use a blue filter instead of a yellow filter E) Move the light source further away from the slits

Q: Light from a point source X contains only blue and red components. After passing through a mysterious box, the light falls on a screen. Red and blue hands are observed as shown. The box must contain: A) a lens B) a mirror C) a prism D) a double slit E) a blue and red filter

Q: In an experiment to measure the wavelength of light using a double slit, it is found that the fringes are too close together to easily count them. To spread out the fringe pattern, one could: A) halve the slit separation B) double the slit separation C) double the width of each slit D) halve the width of each slit E) none of these

Q: In a Young's double-slit experiment, the slit separation is doubled. This results in: A) an increase in fringe intensity B) a decrease in fringe intensity C) a halving of the wavelength D) a halving of the fringe spacing E) a doubling of the fringe spacing

Q: In a Young's double-slit experiment, the separation between slits is d and the screen is a distance D from the slits. D is much greater than dand is the wavelength of the light. The number of bright fringes per unit length on the screen is:

Q: In a Young's double-slit experiment, light of wavelength 500 nm illuminates two slits which are separated by 1 mm. The separation between adjacent bright fringes on a screen 5 m from the slits is: A) 0.10 cm B) 0.25 cm C) 0.50 cm D) 1.0 cm E) none of the above

Q: In a Young's double-slit experiment, the slit separation is doubled. To maintain the same fringe spacing on the screen, the screen-to-slit distance Dmust be changed to: A) D/2 B) C) D) 2D E) 4D

Q: A monochromatic light source illuminates a double slit and the resulting interference pattern is observed on a distant screen. Let dbe the center-to-center slit spacing, athe individual slit width, Dthe screen-to-slit distance, and â„“ the adjacent dark line spacing in the interference pattern. The wavelength of the light is then: A) B) C) da/D D) E)

Q: Waves from two slits are in phase at the slits and travel to a distant screen to produce the second minimum of the interference pattern. The difference in the distance traveled by the wave is: A) half a wavelength B) a wavelength C) three halves of a wavelength D) two wavelengths E) three wavelengths

Q: Waves from two slits are in phase at the slits and travel to a distant screen to produce the third bright fringe of the interference pattern. The difference in the distance traveled by the waves is: A) half a wavelength B) a wavelength C) three halves of a wavelength D) two wavelengths E) three wavelengths

Q: In a Young's double-slit experiment the center of a bright fringe occurs wherever waves from the slits differ in the distance they travel by a multiple of: A) a fourth of a wavelength B) a half a wavelength C) three-fourths of a wavelength D) a wavelength E) none of the above

Q: The reason there are two slits, rather than one, in a Young's experiment is: A) to increase the intensity B) one slit is for frequency, the other for wavelength C) to create a path length difference D) one slit is for fields, the other is for fields E) two slits in parallel offer less resistance

Q: The phase difference between the two waves which give rise to a dark spot in a Young's double-slit experiment is (where m= integer):

Q: Two point sources, vibrating in phase, produce an interference pattern in a ripple tank. If the frequency is increased by 20%, the number of nodal lines: A) is increased by 20% B) is increased by 40% C) remains the same D) is decreased by 20% E) is decreased by 40%

Q: In a Young's double-slit experiment the center of a bright fringe occurs wherever waves from the slits differ in phase by a multiple of:

Q: Two light waves are initially in phase and have the same wavelength, 470 nm. They enter two different media of identical lengths of 2.50 m. If n1= 1.2 and n2= 1.5, what is the effective phase difference of the waves when they exit the media? A) 0 rad B) 0.6 rad C) 1.6 rad D) 3.7 rad E) 10 rad

Q: The light waves represented by the three rays shown in the diagram all have the same frequency. 4.7 wavelengths fit into layer 1, 3.2 wavelengths fit into layer 2, and 5.3 wavelengths fit into layer 3. Rank the layers according to the speeds of the waves, least to greatest. A) 1, 2, 3 B) 2, 1, 3 C) 3, 1, 2 D) 3, 2, 1 E) 1, 3, 2

Q: If the wavelength of a particular beam of light in vacuum is , and the index of refraction of a material is n, what is the wavelength of the light in the material?

Q: When light travels from one medium into a different medium with a different index of refraction, A) the frequency, wavelength, and speed all change. B) the frequency and wavelength change but the speed stays the same. C) the speed and wavelength change but the frequency stays the same. D) the speed and frequency change but the wavelength stays the same. E) only the speed changes; the frequency and the wavelength stay the same.

Q: If the speed of light is c, and the index of refraction of a material is n, what is the speed of light in the material? A) c B) c/n C) nc D) n E) n/c

Q: Interference of light is evidence that: A) the speed of light is very large B) light is a transverse wave C) light is electromagnetic in character D) light is a wave phenomenon E) light does not obey conservation of energy

Q: Units of "optical path length" are:A) m-1B) mC) m/sD) Hz/mE) m/Hz

Q: Consider (I) the law of reflection and (II) the law of refraction. Huygens' principle can be used to derive: A) only I B) only II C) both I and II D) neither I nor II E) the question is meaningless because Huygens' principle is for wave fronts whereas both I and II concern rays

Q: Huygens' construction can be used only: A) for light B) for an electromagnetic wave C) if one of the media is vacuum (or air) D) for transverse waves E) for all of these and other situations

Q: A "wave front" is a surface of constant: A) phase B) frequency C) wavelength D) amplitude E) speed

Q: The objective lens of the Yerkes telescope (the largest functioning refracting telescope in the world) has a focal length of 19.4 m. If its eyepiece has a focal length of 2.5 cm, what is the magnitude of its magnification? A) 7.8 B) 13 C) 130 D) 780 E) cannot be calculated without knowing the length of the telescope

Q: In a compound microscope, the objective has a focal length of 1.0 cm, the eyepiece has a focal length of 2.0 cm, and the tube length is 25 cm. What is the magnitude of the overall magnification of the microscope? A) 25 B) 50 C) 100 D) 250 C) 310

Q: Consider the following four statements concerning a compound microscope: I. Each lens produces an image that is virtual and inverted. II. The objective lens has a very short focal length. III. The eyepiece is used as a simple magnifying glass. IV. The objective lens is convex and the eyepiece is concave. Which two of the four statements are correct? A) I, II B) I, III C) I, IV D) II, III E) II, IV

Q: Letfoandfebe the focal lengths of the objective and eyepiece of a compound microscope. In ordinary use, the object: A) is less thanfofrom the objective lens B) is more thatfofrom the objective C) produces an intermediate image which is slightly more thanfefrom the eyepiece D) produces an intermediate image which is 2feaway from the eyepiece E) produces an intermediate image which is less thanfofrom the objective

Q: A magnifying glass has a focal length of 15 cm. If the near point of the eye is 25 cm from the eye the angular magnification of the glass is about: A) 0.067 B) 0.33 C) 0.5 D) 0.67 E) 1.7

Q: The Sun subtends 0.5°as seen from the Earth. Its image, using a 1.0-m focal length lens, is about:A) 10 cmB) 2 cmC) 1 cmD) 5 mmE) 1 mm

Q: The two lenses shown are illuminated by a beam of parallel light from the left. Lens B is then moved slowly toward lens A. The beam emerging from lens B is: A) initially parallel and then diverging B) always diverging C) initially converging and finally parallel D) always parallel E) initially converging and finally diverging

Q: In a two lens microscope, the intermediate image is: A) virtual, erect and magnified B) real, erect and magnified C) real, inverted and magnified D) virtual, inverted and reduced E) virtual, inverted and magnified

Q: Which of the following is NOT correct for a simple magnifying glass? A) the image is virtual B) the image is erect C) the image is larger than the object D) the object is inside the focal point E) the lens is diverging

Q: Which instrument uses a single converging lens with the object placed just inside the focal point? A) Camera B) Compound microscope C) Magnifying glass D) Overhead projector E) Telescope

Q: An ordinary magnifying glass in front of an erect object produces an image that is: A) real and erect B) real and inverted C) virtual and inverted D) virtual and erect E) none of these

Q: A converging lens of focal length 20 cm is placed in contact with, and to the left of, a diverging lens of focal length 30 cm. If an object is placed 40 cm to the left of the converging lens, the total magnification is:A) -3.0B) -1.5C) -1.0D) 2.0E) 3.0

Q: Two thin lenses (focal lengthsf1andf2) are in contact. Their equivalent focal length is:A) f1+f2B) f1f2/(f1+f2)C) 1/f1+ 1/f2D) f1-f2E) f1(f1-f2)/f2

Q: A converging lens of focal length 20 cm is placed in contact with a diverging lens of focal length 30 cm. The focal length of this combination is:A) +60 cmB) +25 cmC) +12 cmD) +10 cmE) -10 cm

Q: An object is 20 cm to the left of a lens of focal length +10 cm. A second lens, of focal length +12.5 cm, is 30 cm to the right of the first lens. The distance between the original object and the final image is: A) 0 cm B) 28 cm C) 50 cm D) 100 cm E) infinite

Q: A converging lens is symmetric; its curved sides have radii of 50 cm. If the focal length is to be 80 cm, what should the index of refraction be? A) 0 B) 0.3 C) 0.6 D) 1.3 E) 1.6

Q: A plano-convex glass (n= 1.5) lens has a curved side whose radius is 50 cm. If the image size is to be the same as the object size, the object should be placed at a distance from the lens of: A) 50 cm B) 100 cm C) 200 cm D) 340 cm E) 400 cm

Q: An erect object is 2f in front of a convex lens of focal lengthf.The image is: A) real, inverted, magnified B) real, erect, same size C) real, inverted, same size D) virtual, inverted, reduced E) real, inverted, reduced

Q: The object-lens distance for a certain converging lens is 400 mm. The image is three times the size of the object. To make the image five times the size of the object, the object-lens distance must be changed to: A) 360 mm B) 540 mm C) 600 mm D) 720 mm E) 960 mm

Q: A camera with a lens of focal length 6.0 cm takes a picture of a 1.4-m man standing 11 m away. The height of the image is about: A) 0.39 cm B) 0.77 cm C) 1.5 cm D) 3.0 cm E) 6.0 cm

Q: Let pdenote the object-lens distance and ithe image-lens distance. The image produced by a lens of focal lengthf has a height that can be obtained from the object height by multiplying it by: A) p/i B) i/p C) f/p D) f/i E) i/f

Q: An object is 30 cm in front of a converging lens of focal length 10 cm. The image is: A) real and larger than the object B) real and the same size than the object C) real and smaller than the object D) virtual and the same size than the object E) virtual and smaller than the object

Q: An erect object is placed on the central axis of a thin lens, further from the lens than the magnitude of its focal length. The magnification is +0.4. This means: A) the image is real and erect and the lens is a converging lens B) the image is real and inverted and the lens is a converging lens C) the image is virtual and erect, and the lens is a diverging lens D) the image is virtual and erect, and the lens is a converging lens E) the image is virtual and inverted and the lens is a diverging lens

Q: A 3-cm high object is in front of a thin lens. The object distance is 4 cm and the image distance is "8 cm. The image height is: A) 0.5 cm B) 1 cm C) 1.5 cm D) 6 cm E) 24 cm

Q: In a cinema, a picture 2.5 cm wide on the film is projected to an image 3.0 m wide on a screen which is 18 m away. The focal length of the lens is about: A) 7.5 cm B) 10 cm C) 12.5 cm D) 15 cm E) 20 cm

Q: When a single-lens camera is focused on a distant object, the lens-to-film distance is found to be 40.0 mm. To focus on an object 0.540 m in front of the lens, the film-to-lens distance should be: A) 36.8 mm B) 37.3 mm C) 40.0 mm D) 42.7 mm E) 43.2 mm

Q: The bellows of an adjustable camera can be extended so that the largest film to lens distance is one and one-half times the focal length. If the focal length is 12 cm, the nearest object which can be sharply focused on the film must be what distance from the lens? A) 12 cm B) 24 cm C) 36 cm D) 48 cm E) 72 cm

Q: A hollow lens is made of thin glass as shown. It can be filled with air, water (n= 1.3) or CS2(carbon disulfide, n= 1.6). A beam of parallel light entering the lens will diverge if the lens is filled with: A) air and immersed in air B) air and immersed in water C) water and immersed in CS2 D) CS2and immersed in water E) CS2and immersed in CS2

Q: If the image distance is negative, A) the image is real. B) the image is virtual. C) the lens is converging. D) the object distance must also be negative. E) this is not possible; the image distance must be positive.

Q: Which type(s) of lenses can produce both real and virtual images? A) only diverging lenses B) only converging lenses C) only plane lenses D) both converging and diverging lenses E) neither converging nor diverging lenses

Q: An object is in front of a converging lens, at a distance less than the focal length from the lens. Its image is: A) virtual and larger than the object B) real and smaller than the object C) virtual and smaller than the object D) real and larger than the object E) virtual and the same size as the object

Q: An erect object placed outside the focal point of a converging lens will produce an image that is: A) erect and virtual B) inverted and virtual C) erect and real D) inverted and real E) impossible to locate

Q: Where must an object be placed in front of a converging lens in order to obtain a virtual image? A) At the focal point B) At twice the distance to the focal point C) Anywhere beyond the focal point D) Between the focal point and the lens E) Between the focal point and twice the distance to the focal point

Q: Which of the following five glass lenses is a diverging lens? A) I B) II C) III D) IV E) V

Q: An object faces a spherical refracting surface. If ris negative, A) the surface is convex. B) the surface is concave. C) the image must be real. D) the object distance must be negative. E) this cannot happen; rmust be positive.

Q: A convex spherical refracting surface separates a medium with index of refraction 2 from air. The image of an object outside the surface is real: A) always B) never C) only if it is close to the surface D) only if its distance from the surface is large compared to the radius of curvature E) only if the radius of curvature is small

Q: A convex refracting surface has a radius of 12 cm. Light is incident in air (n= 1) and refracted into a medium with an index of refraction of 2. To obtain light with rays parallel to the central axis after refraction a point source should be placed on the axis: A) 3 cm from the surface B) 6 cm from the surface C) 12 cm from the surface D) 18 cm from the surface E) 24 cm from the surface

Q: A convex refracting surface has a radius of 12 cm. Light is incident in air (n= 1) and refracted into a medium with an index of refraction of 2. Light incident parallel to the central axis is focused at a point: A) 3 cm from the surface B) 6 cm from the surface C) 12 cm from the surface D) 18 cm from the surface E) 24 cm from the surface

Q: A concave spherical surface with radius rseparates a medium with index of refraction 2 from air. As an object in air is moved toward the surface from far away along the central axis, its image: A) changes from virtual to real when it is a distancer/2 from the surface B) changes from virtual to real when it is a distance 2rfrom the surface C) changes from real to virtual when it is a distance r/2 from the surface D) changes from real to virtual when it is a distance 2rfrom the surface E) remains virtual