Physics Principles with Applications

Douglas C. Giancoli

Chapter 23

Light: Geometric Waves - all with Video Answers

Educators

Chapter Questions

Problem 1

(I) Suppose that you want to take a photograph of yourself as you look at your image in a flat mirror 2.5 $\mathrm{m}$ away. For what distance should the camera lens be focused?

Katie Mcalpine

Katie Mcalpine

Numerade Educator

Problem 2

(I) When you look at yourself in a 60 -cm-tall plane mirror, you see the same amount of your body whether you are close to the mirror or far away. (Try it and see.) Use ray diagrams to show why this should be true.

Christopher Provencher

Christopher Provencher

Numerade Educator

Problem 3

(II) Two mirrors meet at a $135^{\circ}$ angle, Fig. $23-47 .$ If light rays strike one mirror at $40^{\circ}$ as shown, at what angle $\phi$ do they leave the second mirror?

Katie Mcalpine

Numerade Educator

Problem 4

(II) A person whose eyes are 1.68 $\mathrm{m}$ above the floor stands 2.20 $\mathrm{m}$ in front of a vertical plane mirror whose bottom edge is 43 $\mathrm{cm}$ above the floor, Fig. $23-48$ . What is the horizontal distance $x$ to the base of the wall supporting the mirror of the nearest point on the floor that can be seen reflected in the mirror?

Katie Mcalpine

Numerade Educator

Problem 5

(II) Suppose you are 90 $\mathrm{cm}$ from a plane mirror. What area of the mirror is used to reflect the rays entering one eye from a point on the tip of your nose if your pupil diameter is 5.5 $\mathrm{mm} ?$

Katie Mcalpine

Numerade Educator

Problem 6

(III) Show that if two plane mirrors meet at an angle $\phi,$ a single ray reflected successively from both mirrors is deflected through an angle of 2$\phi$ independent of the incident angle. Assume $\phi < 90^{\circ}$ and that only two reflections, one from each mirror, take place.

Katie Mcalpine

Numerade Educator

Problem 7

(I) A solar cooker, really a concave mirror pointed at the Sun, focuses the Sun's rays 18.0 $\mathrm{cm}$ in front of the mirror. What is the radius of the spherical surface from which the mirror was made?

Katie Mcalpine

Numerade Educator

Problem 8

(I) How far from a concave mirror (radius 23.0 $\mathrm{cm} )$ must an object be placed if its image is to be at infinity?

Katie Mcalpine

Numerade Educator

Problem 9

(II) If you look at yourself in a shiny Christmas tree ball with a diameter of 9.0 $\mathrm{cm}$ when your face is 30.0 $\mathrm{cm}$ away from it, where is your image? Is it real or virtual? Is it upright or inverted?

Katie Mcalpine

Numerade Educator

Problem 10

(II) A mirror at an amusement park shows an upright image of any person who stands 1.4 $\mathrm{m}$ in front of it. If the image is three times the person's height, what is the radius of curvature?

Katie Mcalpine

Numerade Educator

Problem 11

(II) A dentist wants a small mirror that, when 2.20 $\mathrm{cm}$ from a tooth, will produce a $4.5 \times$ upright image. What kind of mirror must be used and what must its radius of curvature be?

Katie Mcalpine

Numerade Educator

Problem 12

(II) Some rearview mirrors produce images of cars behind you that are smaller than they would be if the
mirror were flat. Are the mirrors concave or convex? What is a mirror's radius of curvature if cars 20.0 $\mathrm{m}$ away appear $0.33 \times$ their normal size?

Katie Mcalpine

Numerade Educator

Problem 13

(II) A luminous object 3.0 $\mathrm{mm}$ high is placed 20.0 $\mathrm{cm}$ from a convex mirror of radius of curvature $20.0 \mathrm{cm} .(a)$ Show by ray tracing that the image is virtual, and estimate the image distance. (b) Show that the (negative) image distance can be computed from Eq. $23-2$ using a focal length of $-10.0 \mathrm{cm} .(c)$ Compute the image size, using Eq. $23-3 .$

Katie Mcalpine

Numerade Educator

Problem 14

(II) You are standing 3.0 $\mathrm{m}$ from a convex security mirror in a store. You estimate the height of your image to be half of your actual height. Estimate the radius of curvature of the mirror.

Bruce Edelman

Numerade Educator

Problem 15

(II) $(a)$ Where should an object be placed in front of a concave mirror so that it produces an image at the same location as the object? $(b)$ Is the image real or virtual? (c) Is the image inverted or upright? (d) What is the magnification of the image?

Bruce Edelman

Numerade Educator

Problem 16

(II) The image of a distant tree is virtual and very small when viewed in a curved mirror. The image appears to be 18.0 $\mathrm{cm}$ behind the mirror. What kind of mirror is it, and what is its radius of curvature?

Katie Mcalpine

Numerade Educator

Problem 17

(II) Use two different techniques, $(a)$ a ray diagram, and (b) the mirror equation, to show that the magnitude of the magnification of a concave mirror is less than 1 if the object is beyond the center of curvature $C\left(d_{0}>r\right),$ and is greater than 1 if the object is within $C\left(d_{0}<r\right) .$

Katie Mcalpine

Numerade Educator

Problem 18

(II) Show, using a ray diagram, that the magnification $m$ of a convex mirror is $m=-d_{1} / d_{0},$ just as for a concave mirror. [Hint: consider a ray from the top of the object that reflects at the center of the mirror.]

Christopher Provencher

Christopher Provencher

Numerade Educator

Problem 19

(II) Use ray diagrams to show that the mirror equation, Eq. $23-2$ , is valid for a convex mirror as long as $f$ is considered negative.

Mayukh Banik

Numerade Educator

Problem 20

(II) The magnification of a convex mirror is $+0.65 \times$ for objects 2.2 $\mathrm{m}$ from the mirror. What is the focal length of this mirror?

Katie Mcalpine

Numerade Educator

Problem 21

(III) A 4.5$\cdot$ -cm-tall object is placed 28 $\mathrm{cm}$ in front of a spherical mirror. It is desired to produce a virtual image that is upright and 3.5 $\mathrm{cm}$ tall. (a) What type of mirror should be used? (b) Where is the image located? (c) What is the focal length of the mirror? (d) What is the radius of curvature of the mirror?

Katie Mcalpine

Numerade Educator

Problem 22

(III) A shaving/makeup mirror is designed to magnify your face by a factor of 1.33 when your face is placed 20.0 $\mathrm{cm}$ in front of it. $(a)$ What type of mirror is it? (b) Describe the type of image that it makes of your face. (c) Calculate the required radius of curvature for the mirror.

Katie Mcalpine

Numerade Educator

Problem 23

(I) What is the speed of light in (a) crown glass, (b) Lucite, and ( $c$ ) ethyl alcohol?

Melissa Walsh

Numerade Educator

Problem 24

(1) The speed of light in ice is $2.29 \times 10^{8} \mathrm{m} / \mathrm{s}$ . What is the index of refraction of ice?

Katie Mcalpine

Numerade Educator

Problem 25

(II) The speed of light in a certain substance is 89$\%$ of its value in water. What is the index of refraction of this substance?

Katie Mcalpine

Numerade Educator

Problem 26

(I) A flashlight beam strikes the surface of a pane of glass $(n=1.58)$ at a $63^{\circ}$ angle to the normal. What is the angle of refraction?

Katie Mcalpine

Numerade Educator

Problem 27

(I) A diver shines a flashlight upward from beneath the water at a $42.5^{\circ}$ angle to the vertical. At what angle does the light leave the water?

Katie Mcalpine

Numerade Educator

Problem 28

(I) A light beam coming from an underwater spotlight exits the water at an angle of $66.0^{\circ}$ to the vertical. At what angle of incidence does it hit the air-water interface from below the surface?

Katie Mcalpine

Numerade Educator

Problem 29

(1) Rays of the Sun are seen to make a $31.0^{\circ}$ angle to the vertical beneath the water. At what angle above the horizon is the Sun?

Katie Mcalpine

Numerade Educator

Problem 30

(II) An aquarium filled with water has flat glass sides whose index of refraction is $1.52 .$ A beam of light from outside the aquarium strikes the glass at a $43.5^{\circ}$ angle to the perpendicular (Fig. $23-49 ) .$ What is the angle of this light ray when it enters $(a)$ the glass, and then $(b)$ the water? (c) What would be the refracted angle if the ray entered the water directly?

Katie Mcalpine

Numerade Educator

Problem 31

(II) In searching the bottom of a pool at night, a watchman shines a narrow beam of light from his flash-
light, 1.3 $\mathrm{m}$ above the water level, onto the surface of the water at a point 2.7 $\mathrm{m}$ from the edge of the pool (Fig. $23-50 )$ . Where does the spot of light hit the bottom of the pool, measured from the wall beneath his foot, if the pool is 2.1 $\mathrm{m}$ deep?

Katie Mcalpine

Numerade Educator

Problem 32

(II) Light is incident on an equilateral glass prism at a $45.0^{\circ}$ angle to one face, Fig. $23-51 .$ Calculate the angle at which light emerges from the opposite face. Assume that $n=1.58 .$

Katie Mcalpine

Numerade Educator

Problem 33

(II) A beam of light in air strikes a slab of glass $(n=1.52)$ and is partially reflected and partially
refracted. Find the angle of incidence if the angle of reflection is twice the angle of refraction.

Katie Mcalpine

Numerade Educator

Problem 34

(III) Prove in general that for a light beam incident on a uniform layer of transparent material, as in Fig. $23-22$ , the direction of the emerging beam is parallel to the incident beam, independent of the incident angle $\theta .$ Assume air on both sides of the glass.

Katie Mcalpine

Numerade Educator

Problem 35

(III) A light ray is incident on a flat piece of glass with index of refraction $n$ as in Fig. $23-22$ . Show that if the incident angle $\theta$ is small, the emerging ray is displaced a distance $d=t \theta(n-1) / n$ from the incident ray, where $t$ is the thickness of the glass and $\theta$ is in radians. $[\text {Hint: for }$ small $\theta, \sin \theta \approx \tan \theta \approx \theta$ in radians. $]$

Christopher Provencher

Christopher Provencher

Numerade Educator

Problem 36

(I) What is the critical angle for the interface between water and Lucite? To be totally internally reflected, the light must start in which material?

Katie Mcalpine

Numerade Educator

Problem 37

(I) The critical angle for a certain liquid-air surface is $47.7^{\circ} .$ What is the index of refraction of the liquid?

Katie Mcalpine

Numerade Educator

Problem 38

(II) A beam of light is emitted in a pool of water from a depth of $62.0 \mathrm{cm} .$ Where must it strike the air-water interface, relative to the spot directly above it, in order that the light does not exit the water?

Katie Mcalpine

Numerade Educator

Problem 39

(II) A beam of light is emitted 8.0 $\mathrm{cm}$ beneath the surface of a liquid and strikes the surface 7.0 $\mathrm{cm}$ from the point directly above the source. If total internal reflection occurs, what can you say about the index of refraction of the liquid?

Katie Mcalpine

Numerade Educator

Problem 40

(III) Suppose a ray strikes the left face of the prism in Fig. $23-51$ at $45.0^{\circ}$ as shown, but is totally internally reflected at the opposite side. If the prism apex angle (at the top ) is $\phi=75.0^{\circ}$ , what can you say about the index of refraction of the prism?

Katie Mcalpine

Numerade Educator

Problem 41

(III) A beam of light enters the end of an optic fiber as shown in Fig. $23-52$ . Show that we can guarantee total internal reflection at the side surface of the material (at point a), if the index of refraction is greater than about $1.42 .$ In other words, regardless of the angle $\alpha,$ the light beam reflects back into the material at point a.

Katie Mcalpine

Numerade Educator

Problem 42

(III) (a) What is the minimum index of refraction for a glass or plastic prism to be used in binoculars (Fig. $23-26$ ) so that total internal reflection occurs at $45^{\circ} ?(b)$ Will binoculars work if its prisms (assume $n=1.50 )$ are immersed in water? $(c)$ What minimum $n$ is needed if the prisms are immersed in water?

Mayukh Banik

Numerade Educator

Problem 43

(I) A sharp image is located 78.0 $\mathrm{mm}$ behind a 65.0 $\mathrm{mm}$ - focal-length converging lens. Find the object distance (a) using a ray diagram, ( $b$ ) by calculation.

Katie Mcalpine

Numerade Educator

Problem 44

(1) Sunlight is observed to focus at a point 18.5 $\mathrm{cm}$ behind a lens. ( $a$ ) What kind of lens is it? (b) What is its power in diopters?

Katie Mcalpine

Numerade Educator

Problem 45

(I) A certain lens focuses light from an object 2.75 $\mathrm{m}$ away as an image 48.3 $\mathrm{cm}$ on the other side of the lens. What type of lens is it and what is its focal length? Is the image real or virtual?

Katie Mcalpine

Numerade Educator

Problem 46

(I) $(a)$ What is the power of a 20.5 -cm-focal-length lens? (b) What is the focal length of a $-6.25$ -diopter lens? (c) Are these lenses converging or diverging?

Katie Mcalpine

Numerade Educator

Problem 47

(II) A stamp collector uses a converging lens with focal length 24 $\mathrm{cm}$ to view a stamp 18 $\mathrm{cm}$ in front of the lens. (a) Where is the image located? (b) What is the magnification?

Katie Mcalpine

Numerade Educator

Problem 48

(II) A $-5.5 \cdot$ D lens is held 14.0 $\mathrm{cm}$ from an object 4.0 $\mathrm{mm}$ high. What are the position, type, and height of the image?

Katie Mcalpine

Numerade Educator

Problem 49

(II) An 80 -mm-focal-length lens is used to focus an image on the film of a camera. The maximum distance allowed between the lens and the film plane is 120 $\mathrm{mm}$ . (a) How far ahead of the film should the lens be if the object to be photographed is 10.0 $\mathrm{m}$ away? (b) 3.0 $\mathrm{m}$ away? (c) 1.0 $\mathrm{m}$ away? (d) What is the closest object this lens could photograph sharply?

Vishal Gupta

Numerade Educator

Problem 50

(II) It is desired to magnify reading material by a factor of $2.5 \times$ when a book is placed 8.0 $\mathrm{cm}$ behind a lens. (a) Draw a ray diagram and describe the type of image this would be. ( $b$ ) What type of lens is needed? (c) What is the power of the lens in diopters?

Katie Mcalpine

Numerade Educator

Problem 51

(II) An object is located 1.5 $\mathrm{m}$ from an $8.0 . \mathrm{D}$ lens. By how much does the image move if the object is moved (a) 1.0 $\mathrm{m}$ closer to the lens, and ( $b ) 1.0 \mathrm{m}$ farther from the lens?

Katie Mcalpine

Numerade Educator

Problem 52

(II) How far from a converging lens with a focal length of 25 $\mathrm{cm}$ should an object be placed to produce a real image which is the same size as the object?

Carlos Henrique De Lima

Carlos Henrique De Lima

Numerade Educator

Problem 53

(II) $(a)$ How far from a 50.0 -mm-focal-length lens must an object be placed if its image is to be magnified $2.00 \times$ and be real? (b) What if the image is to be virtual and magnified $2.00 \times ?$

Mayukh Banik

Numerade Educator

Problem 54

(II) Repeat Problem 53 for a $-50.0$ -mm-focal-length lens. [Hint: consider objects real or virtual (formed by some other piece of optics). $]$

Mayukh Banik

Numerade Educator

Problem 55

(II) $(a)$ A 2.00 -cm-high insect is 1.20 $\mathrm{m}$ from a 135 $\mathrm{-mm}$ - focal-length lens. Where is the image, how high is it, and what type is it? (b) What if $f=-135 \mathrm{mm}$ ?

Katie Mcalpine

Numerade Educator

Problem 56

(III) How far apart are an object and an image formed by a $75-$ -focal-length converging lens if the image is $2.5 \times$ larger than the object and is real?

Katie Mcalpine

Numerade Educator

Problem 57

(III) A bright object and a viewing screen are separated by a distance of 66.0 $\mathrm{cm}$ . At what location $(\mathrm{s})$ between the object and the screen should a lens of focal length 12.5 $\mathrm{cm}$ be placed in order to produce a crisp image on the screen? [Hint. first draw a diagram.]

Dading Chen

Numerade Educator

Problem 58

(II) Two 28.0 -cm-focal-length converging lenses are placed 16.5 $\mathrm{cm}$ apart. An object is placed 36.0 $\mathrm{cm}$ in front of one lens. Where will the final image formed by the second lens be located? What is the total magnification?

Katie Mcalpine

Numerade Educator

Problem 59

(II) A diverging lens with $f=-31.5 \mathrm{cm}$ is placed 14.0 $\mathrm{cm}$ behind a converging lens with $f=20.0 \mathrm{cm} .$ Where will an object at infinity be focused?

Katie Mcalpine

Numerade Educator

Problem 60

(II) A 31.0 -cm-focal-length converging lens is 21.0 $\mathrm{cm}$ behind a diverging lens. Parallel light strikes the diverging lens. After passing through the converging lens, the light is again parallel. What is the focal length of the diverging lens? [Hint: first draw a ray diagram. $]$

Mayukh Banik

Numerade Educator

Problem 61

(II) The two converging lenses of Example $23-12$ are now placed only 20.0 $\mathrm{cm}$ apart. The object is still 60.0 $\mathrm{cm}$ in front of the first lens as in Fig. $23-41 .$ In this case, determine (a) the position of the final image, and $(b)$ the overall magnification. (c) Sketch the ray diagram for this system.

Mayukh Banik

Numerade Educator

Problem 62

(II) Two converging lenses are placed 30.0 $\mathrm{cm}$ apart. The focal length of the lens on the right is $20.0 \mathrm{cm},$ and the focal length of the lens on the left is $15.0 \mathrm{cm} .$ An object is placed to the left of the 15.0 -cm-focal-length lens, A final image from both lenses is inverted and located halfway between the two lenses. How far to the left of the 15.0 -cm-focal-length lens is the original object?

Mayukh Banik

Numerade Educator

Problem 63

(II) A diverging lens with a focal length of $-14 \mathrm{cm}$ is placed 12 $\mathrm{cm}$ to the right of a converging lens with a focal length of $18 \mathrm{cm} .$ An object is placed 33 $\mathrm{cm}$ to the left of the converging lens. (a) Where will the final image be located? (b) Where will the image be if the diverging lens is 38 $\mathrm{cm}$ from the converging lens?

Mayukh Banik

Numerade Educator

Problem 64

(II) Two lenses, one converging with focal length 20.0 $\mathrm{cm}$ and one diverging with focal length $-10.0 \mathrm{cm}$ , are placed 25.0 $\mathrm{cm}$ apart. An object is placed 60.0 $\mathrm{cm}$ in front of the converging lens. Determine (a) the position and (b) the magnification of the final image formed. (c) Sketch a ray diagram for this system.

Carlos Henrique De Lima

Carlos Henrique De Lima

Numerade Educator

Problem 65

(III) A diverging lens is placed next to a converging lens of focal length $f_{C},$ as in Fig. $23-42$ . If $f_{\mathrm{T}}$ represents the focal length of the combination, show that the focal length of the diverging lens, $f_{\mathrm{D}}$ , is given by
$$
\frac{1}{f_{\mathrm{D}}}=\frac{1}{f_{\mathrm{T}}}-\frac{1}{f_{\mathrm{C}}}
$$

Mayukh Banik

Numerade Educator

Problem 66

(I) A double concave lens has surface radii of 34.2 $\mathrm{cm}$ and $23.8 \mathrm{cm} .$ What is the focal length if $n=1.52 ?$

Mayukh Banik

Numerade Educator

Problem 67

(I) Both surfaces of a double convex lens have radii of 31.0 $\mathrm{cm}$ . If the focal length is $28.9 \mathrm{cm},$ what is the index of refraction of the lens material?

Mayukh Banik

Numerade Educator

Problem 68

(II) A planoconcave lens $(n=1.50)$ has a focal length of $-23.4 \mathrm{cm} .$ What is the radius of the concave surface?

Mayukh Banik

Numerade Educator

Problem 69

(II) A Lucite planoconcave lens (see Fig. $23-29$ b) hat is the flat surface and the other has $R=-18.4 \mathrm{cm} .$ What is the focal length?

Mayukh Banik

Numerade Educator

Problem 70

(II) A symmetric double convex lens with a focal length of 25.0 $\mathrm{cm}$ is to be made from glass with an index of refraction of $1.52 .$ What should be the radius of curvature for each surface?

Mayukh Banik

Numerade Educator

Problem 71

(II) A prescription for a corrective lens calls for $+1.50 \mathrm{D}$ . The lensmaker grinds the lens from a "blank" with $n=1.56$ and a preformed convex front surface of radius of curvature of $40.0 \mathrm{cm} .$ What should be the radius of curvature of the other surface?

Mayukh Banik

Numerade Educator

Problem 72

Two plane mirrors face each other 2.0 $\mathrm{m}$ apart as in Fig. $23-53 .$ You stand 1.5 $\mathrm{m}$ away from one of these mirrors and look into it. You will see multiple images of yourself. (a) How far away from you are the first three images in the mirror in front of you? (b) Are these first three images facing toward you or away from you?

Mayukh Banik

Numerade Educator

Problem 73

We wish to determine the depth of a swimming pool filled with water. We measure the width $(x=5.50 \mathrm{m})$ and then note that the bottom edge of the pool is just visible at an angle of $14.0^{\circ}$ above the horizontal as shown in Fig. $23-54$ . Calculate the depth of the pool.

Mayukh Banik

Numerade Educator

Problem 74

The critical angle of a certain piece of plastic in air is $\theta_{\mathrm{C}}=37.3^{\circ} .$ What is the critical angle of the same plastic if it is immersed in water?

Mayukh Banik

Numerade Educator

Problem 75

(a) A plane mirror can be considered a limiting case of a spherical mirror. Specify what this limit is. (b) Determine an equation that relates the image and object distances in this limit of a plane mirror. (c) Determine the magnification of a plane mirror in this same limit. (d) Are your results in parts $(b)$ and $(c)$ consistent with the discussion of Section $23-2$ on plane mirrors?

Pronoy Sinha

Numerade Educator

Problem 76

Stand up two plane mirrors so they form a $90^{\circ}$ angle as in Fig. $23-55$ . When you look into this double mirror, you see yourself as others see you, instead of reversed as in a single mirror. Make a careful ray diagram to show how this occurs.

Mayukh Banik

Numerade Educator

Problem 77

Show analytically that a diverging lens can never form a real image of a real object. Can you describe a situation in which a diverging lens can form a real image?

Mayukh Banik

Numerade Educator

Problem 78

Each student in a physics lab is assigned to find the location where a bright object may be placed in order that a concave mirror with radius of curvature $r=40 \mathrm{cm}$ will produce an image three times the size of the object. Two students complete the assignment at different times using identical equipment, but when they compare notes later, they discover that their answers for the object distance are not the same. Explain why they do not necessarily need to repeat the lab, and justify your response with a calculation.

Mayukh Banik

Numerade Educator

Problem 79

If the apex angle of a prism is $\phi=72^{\circ}$ (see Fig. $23-56 )$ what is the minimum incident angle for a ray if it is to emerge from the opposite side (i.e., not be totally internally reflected), given $n=1.50 ?$

Mayukh Banik

Numerade Educator

Problem 80

The end faces of a cylindrical glass rod $(n=1.54)$ are perpendicular to the sides. Show that a light ray entering an end face at any angle will be totally internally reflected inside the rod when the ray strikes the sides. Assume the rod is in air. What if it were in water?

Mayukh Banik

Numerade Educator

Problem 81

A lighted candle is placed 33 $\mathrm{cm}$ in front of a converging lens of focal length $f_{1}=15 \mathrm{cm},$ which in turn is 55 $\mathrm{cm}$ in front of another converging lens of focal length $f_{2}=12 \mathrm{cm}$ (see Fig. $23-57 ) .(a)$ Draw a ray diagram and estimate the location and the relative size of the final image. ( $b$ ) Calculate the position and relative size of the final image.

Mayukh Banik

Numerade Educator

Problem 82

A bright object is placed on one side of a converging lens of focal length $f,$ and a white screen for viewing the image is on the opposite side. The distance $d_{\mathrm{T}}=d_{\mathrm{i}}+d_{\mathrm{o}}$ between the object and the screen is kept fixed, but the lens can be moved. ( $a )$ Show that if $d_{\mathrm{T}}>4 f,$ there will be two positions where the lens can be placed and a sharp image is formed. $(c)$ Determine a formula for the distance between the two lens positions in part $(a),$ and the ratio of the image sizes.

Mayukh Banik

Numerade Educator

Problem 83

In a slide or movie projector, the film acts as the object whose image is projected on a screen (Fig. $23-58$ ). If a 105 -mm-focal-length lens is to project an image on a screen 8.00 $\mathrm{m}$ away, how far from the lens should the slide be? If the slide is 36 $\mathrm{mm}$ wide, how wide will the picture be on the screen?

Narayan Hari

Numerade Educator

Problem 84

A $35-\mathrm{mm}$ slide (picture size is actually 24 by 36 $\mathrm{mm} )$ is to be projected on a screen 1.80 $\mathrm{m}$ by 2.70 $\mathrm{m}$ placed 7.50 $\mathrm{m}$ from the projector. What focal-length lens should be used if the image is to cover the screen?

Mayukh Banik

Numerade Educator

Problem 85

Show analytically that the image formed by a converging lens is real and inverted if the object is beyond the focal point $\left(d_{0}>f\right),$ and is virtual and upright if the object is within the focal point $\left(d_{0}<f\right) .$ Describe the image if the object is itself an image, formed by another lens, so its position is beyond the lens, for which $-d_{0}>f,$ and for which $0<-d_{0}<f$

Mayukh Banik

Numerade Educator

Problem 86

A movie star catches a reporter shooting pictures of her at home. She claims the reporter was trespassing. To prove her point, she gives as evidence the film she seized. Her $1.75-\mathrm{m}$ height is 8.25 $\mathrm{mm}$ high on the film, and the focal length of the camera lens was 210 $\mathrm{mm}$ . How far away from the subject was the reporter standing?

Mayukh Banik

Numerade Educator

Problem 87

How large is the image of the Sun on film used in a camera with $(a)$ a 28 -mm-focal-length lens, (b) a 50 -mm- focal-length lens, and $(c)$ a 135 -mm-focal-length lens? (d) If the $50-\mathrm{mm}$ lens is considered normal for this camera, what relative magnification does each of the other two lenses provide? The Sun has diameter $1.4 \times 10^{6} \mathrm{km},$ and it is $1.5 \times 10^{8} \mathrm{km}$ away.

Carlos Henrique De Lima

Carlos Henrique De Lima

Numerade Educator

Problem 88

(a) An object 34.5 $\mathrm{cm}$ in front of a certain lens is imaged 8.20 $\mathrm{cm}$ in front of that lens (on the same side as the object). What type of lens is this, and what is its focal length? Is the image real or virtual? (b) If the image were located, instead, 41.5 $\mathrm{cm}$ in front of the lens, what type of lens would it be and what focal length would it have?

Mayukh Banik

Numerade Educator

Problem 89

When an object is placed 60.0 $\mathrm{cm}$ from a certain converging lens, it forms a real image. When the object is moved to 40.0 $\mathrm{cm}$ from the lens, the image moves 10.0 $\mathrm{cm}$ farther from the lens. Find the focal length of this lens.

Carlos Henrique De Lima

Carlos Henrique De Lima

Numerade Educator

Problem 90

A small object is 25.0 $\mathrm{cm}$ from a diverging lens as shown in Fig. $23-59 .$ A converging lens with a focal length of 12.0 $\mathrm{cm}$ is 30.0 $\mathrm{cm}$ to the right of the diverging lens. The two-lens system forms a real inverted image 17.0 $\mathrm{cm}$ to the right of the converging lens. What is the focal length of the diverging lens?

Carlos Henrique De Lima

Carlos Henrique De Lima

Numerade Educator

Problem 91

An object is placed 15 $\mathrm{cm}$ from a certain mirror. The image is half the size of the object, inverted, and real. How far is the image from the mirror, and what is the radius of curvature of the mirror?

Bruce Edelman

Numerade Educator

Problem 92

(a) Show that the lens equation can be written in the Newtonian form
$$
x \cdot x^{\prime}=f^{2}
$$
where $x$ is the distance of the object from the focal point on the front side of the lens, and $x^{\prime}$ is the distance of the image to the focal point on the other side of the lens. Calculate the location of an image if the object is placed 45.0 $\mathrm{cm}$ in front of a convex lens with a focal length $f$ of 32.0 $\mathrm{cm}$ using $(b)$ the standard form of the thin lens equation, and $(c)$ the Newtonian form, stated above.

Mayukh Banik

Numerade Educator

Problem 93

A converging lens with focal length of 10.0 $\mathrm{cm}$ is placed in contact with a diverging lens with a focal length of $-20.0 \mathrm{cm} .$ What is the focal length of the combination, and is the combination converging or diverging?

Mayukh Banik

Numerade Educator

Problem 94

(a) Show that if two thin lenses of focal lengths $f_{1}$ and $f_{2}$ are placed in contact with each other, the focal length of the combination is given by $f_{\mathrm{T}}=f_{1} f_{2} /\left(f_{1}+f_{2}\right)$ . (b) Show that the power $P$ of the combination of two lenses is the sum of their separate powers, $P=P_{1}+P_{2}$

Carlos Henrique De Lima

Carlos Henrique De Lima

Numerade Educator