An object is held 75.3 cm away from a lens. The lens has a focal length of 8.2 c

Question

An object is held 75.3 cm away from a lens. The lens has a focal length of 8.2 cm.

a.) Determine the image distance.
cm

b.) Determine the magnification.

c.) If the object is 7 cm long, determine the image height.
cm

d.) Which of the following are true about the image? Choose all that apply.

A.The image is inverted.
B.The image is real.
C.The image is upright.
D.The image is virtual.



e.) Which of the following are true about the lens? Choose all that apply.
A. The lens is diverging.
B. The lens is concave.
C. The lens is converging.
D. The lens is convex.

Explanation / Answer

The focal length f = 8.2cm

the object distance p = 75.3cm

From lens formula

1/f = 1/p + 1/q

therefore the image disatnce

       q = fp/p-f

           = (8.2)(75.3) / 75.3-8.2

           = 9.2 cm

(b) The magnification

          m = -q/p

              = - 9.2/75.3

               = -0.122

(c) If the object heigth ho = 7cm

then the image height hi = m ho

                                     = (-0.122)(7cm)

                                     = - 0.854 cm

(d) Since the object distance is positive so imag eis real and the magnification is neagtive so it is inverted. therefore The image is real and inverted

(e) C. The lens is converging. or
      D. The lens is convex.

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