Question

Following will be two mirrors and two lenses. We are going to find the image distance and the image height for each object.

1. Draw the ray diagrams for each situation properly as accurate as possible.

2. Calculate the image distance with the following data, and compare with drawing.

f=4.0 cm d_o=12.0 cm h_o=3.0 cm

Remember the sign of f depends on the mirror/lens type.

3. Calculate the magnification and image height, and compare with your drawing.

Do this for a concave mirror, convex mirror, converging lens, and a diverging lens.

Answer 1

concave mirror

Focal length is positive

1/f = 1/di + 1/do

di is image distance

1/4 = 1/di + 1/12

1/di = 1/4 - 1/12

di = 6 cm

m = -6/12 = - 0.5

image height = -1.5 cm

The negative sign tells that the image is inverted and real

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convex mirror

focal length is negative

1/di = -1/4 - 1/12

di = -3 cm

m = -(-3) / 12

m = 0.25

image height = 0.75 cm

image is upright and virtual

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converging lens

focal length is positive

1/f = 1/di + 1/do

di is image distance

1/4 = 1/di + 1/12

1/di = 1/4 - 1/12

di = 6 cm

m = -6/12 = - 0.5

image height = -1.5 cm

The negative sign tells that the image is inverted and real

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diverging lens

focal length is negative

1/di = -1/4 - 1/12

di = -3 cm

m = -(-3) / 12

m = 0.25

image height = 0.75 cm

image is upright and virtual