You see a steel gazing ball (like the one on campus) that has a diameter of 2.5

Question

You see a steel gazing ball (like the one on campus) that has a diameter of 2.5 m. It is shiny enough that you can see your reflection in it.

a) The gazing ball is what type of mirror?

plane, concave, convex, or unknown

b) What is the focal length of the gazing ball? Include the sign in your answer.

m

c) As you are walking towards the gazing ball, you stop at a distance of 3.75 m from the surface of the ball. What is your image distance? Include the sign in your answer.

m

d) At the same distance, what is your magnification? Include the sign in your answer.



e) The image of yourself is  ---Select--- real, virtual, unknown ,  ---Select--- upright, inverted, unknown , and  ---Select--- enlarged, reduced, unknown .

Explanation / Answer

a) convex

b) f=-r/2=-(2.5/2)/2=-0.625 m

c) 1/object distance + 1/image distance = 1/focal distance

image distance= f*d/(d-f) = (-0.625)*3.75/(3.75-(-0.625))= -0.535 m

If the lens equation yields a negative image distance, then the image is a virtual image on the same side of the lens as the object.

d) M=f/(f-d) = -0.625/(-0.625-3.75) = 0.14

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