7.5 An object is placed in front of a thin lens at a distance of 7.00 cm, and the lens produces an inverted image that is twice the
size of the object. (a) Is the image height positive or negative? (b) Is the image real or virtual? (c) How far is the image from
the lens? (d) What is the focal length of the lens?
(a) Positive Negative
(b) Real Virtual
(c) cm
(d) cm7.6 An object is placed in front of a thin lens at a distance of 12.0 cm, and the lens produces an upright image that is one-third
the size of the object. (a) Is the image height positive or negative? (b) Is the image real or virtual? (c) Is the image distance
positive or negative? (d) What is the image distance? (e) What is the focal length of the lens?
(a) Positive Negative
(b) Real Virtual
(c) Positive Negative
(d) cm
(e) cm7.7 You are making a thin lens. The near surface (the surface on the object side) has a radius of curvature of +5.00 cm and the
far surface has a radius of curvature of +6.00 cm. What is the focal length of the lens if the index of refraction of the material is
1.60?
cm7.8 The thin lens equation given in this book is sometimes called the Gaussian form of the equation. Another form, called the
Newtonian form, uses the distance x between the object and the first focal point and the distance x' between the second focal
point and the image. Use the Gaussian form to derive the Newtonian form:7.9 A thin lens has a near surface with a radius of curvature of í5.00 cm and a far surface with a radius of curvature of +7.00 cm.
(a) Is the lens converging or diverging? (b) What is the focal length of the lens if the index of refraction of the material is 1.74?
(a) Converging Diverging
(b) cm7.10 A lens has two convex surfaces (both surfaces bulge at the middle). The left surface has a radius of curvature whose
magnitude is 11.2 cm and the right surface has a radius of curvature whose magnitude is 13.0 cm. The index of refraction of
the lens is 1.41. (a) What is the focal length of the lens for light traveling from left to right? (b) What is the focal length of the
lens for light traveling from right to left?
(a) cm
(b) cm
7.11 The cornea and lens of the eye each refract light as it passes into the eye. We consider the cornea and lens together as one
thin lens whose shape, and effective focal length, can be changed by the muscles around the eye. When incoming light is
parallel, such as for an infinitely far away object, the eye muscles shape the effective lens to have a focal length of about
2.50 cm to produce a focused image on the retina. What focal length lens do the muscles cause to create a focused image of
an object 35.0 cm away?
m
7.12 A camera has a lens of focal length 50.0 mm and is focused on an object 0.800 m from the lens. (a) To focus on an object
effectively at infinity, will the lens have to move toward or away from the film? (b) How far will the lens have to move? Give the
answer in millimeters.
(a) Toward Away
(b) mm7.13 A small light bulb is 1.50 meters from a screen. You have a converging lens with a focal length of 0.250 m. There are two
possible distances from the bulb at which you could place the lens to create a sharp image on the screen. What is the larger
of these distances?
mSection 8 - Interactive problem: optical bench with a lens
8.1 Use the information given in the interactive problem in this section to calcuate (a) the object distance and (b) the focal length
of the lens in order to create the desired image. Test your answer using the simulation.
(a) cm
(b) cm