Calculating Di and Hi for Lawn Sphere Mirror Problem

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SUMMARY

The discussion focuses on calculating the image distance (di) and height (hi) for a lawn sphere mirror problem involving a convex mirror with a diameter of 40 cm. The focal length is derived from the radius of curvature, which is half the diameter, yielding a radius of 20 cm. The relevant equations used are 1/f = 1/di + 1/do and hi/ho = -di/do, where do is the object distance of 1.5 m. Participants are guided to first determine the focal length before proceeding to calculate the image characteristics.

PREREQUISITES
  • Understanding of convex mirrors and their properties
  • Familiarity with the mirror equation (1/f = 1/di + 1/do)
  • Knowledge of image height ratio (hi/ho = -di/do)
  • Basic geometry related to circles and spheres
NEXT STEPS
  • Calculate the focal length of a convex mirror using the formula f = r/2
  • Explore the implications of the sign convention for image distance in convex mirrors
  • Practice solving similar problems involving image formation in spherical mirrors
  • Learn about ray diagrams for convex mirrors to visualize image formation
USEFUL FOR

Students studying optics, physics educators, and anyone interested in understanding image formation in convex mirrors.

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Homework Statement


Lawn spheres placed on pedestals are convex mirrors. One such sphere has a diameter of 40.cm. A 12 cm robin sits in a tree 1.5m from the sphere. Make a representative sketch. Where is the image of the robin? How long is the robins image?


Homework Equations


1/f=1/di+1/do
hi/ho=-di/do



The Attempt at a Solution


I have a diagram but am stuck on where to go from here?
 
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Hello Capri,

Welcome to Physics Forums! :smile:

First, work your way to finding the focal length of the mirror.

You know the diameter of the sphere. From that, you can determine the radius of curvature*. From there you should be able to look up some formula for the focal length as a function of the radius of curvature. Oh, and don't forget to pay attention to the +/- sign and how that relates to concave or convex mirrors.

*[Edit: radius of curvature is often called center of curvature.]
 
Last edited:

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