An object is held 42.8 cm away from a lens. The lens has a focal length of -13.1

Question

An object is held 42.8 cm away from a lens. The lens has a focal length of -13.1 cm.

A.) Determine the image distance.
  cm

B.) Determine the magnification.
  

C.) If the object is 3.5 cm long, determine the image height.
  cm
D.) Which of the following are true about the image? Choose all that apply.

The image is real.The image is virtual.The image is inverted.The image is upright.

E.) Which of the following are true about the lens? Choose all that apply. 

The lens is converging.The lens is convex.The lens is diverging.The lens is concave.

Explanation / Answer

Part A)

1/f = 1/p + 1/q

1/-31.1 = 1/42.8 + 1/q

q = -18.0   (or 18.0 cm in front of the lens)

Part B)

M = -q/p = -(-18/42.8)

M = .42

Part C)

M = h'/h

.42 = h'/3.5 = 1.47 cm

Part D)

Since q is negative, the image is virtual

Since M is positive, the image is upright

Part E)

Since the focal length is negative, the lens is diverging.

A diverging lens is concave

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