Question

The end of the spring semester means graduation and receptions. I pick up the empty punch bowl, which is shiny silver on both sides and appears to be a section of a sphere. When I look into the punch bowl I see an image of my face that appears to be 24.0 cm behind the bowl. I flip the bowl over and look at its bottom and now see an image of my face that is 8.00 cm in back of the bowl. I've kept the punch bowl the same distance from my face in each case. How far is this distance between my face and the punch bowl, and what is the radius of curvature of the bowl? Draw and label the ray diagram for either case (you can pick! either looking into the bowl or looking at its back side). 9. Billy is a cruel child who likes to fry ants using a magnifying glass (which is a converging lens). To determine the focal length of the magnifying glass (and hence how far he needs to hold it from an ant to fry it), Billy holds the magnifying glass a distance of 5.0 cm from a penny and sees that the image of the penny is upright (not inverted) and 3.0 times the size of a normal penny. Draw and label the ray diagram for this situation. What is the focal length of his magnifying glass?
Number 9

Answer 1

We have:

- x1=-5cm

-magnification=+3 $\beta =\frac{x_{2}}{x_{1}}$

Thus, x2=-15 cm

Replace in this formula $\frac{1}{x_{2}}-\frac{1}{x_{1}}=\frac{1}{f}$ and get f=+7.5 cm.