QUESTIONS 1. Are R and f positive or negative for a convex mirror? For a concave

Question

QUESTIONS 1. Are R and f positive or negative for a convex mirror? For a concave mirror? 2. Is i positive or negative for a real image formed by a mirror? For a virtual image? 3. Where (on which side of the mirror) are real images formed by a mirror located? 4. Is fpositive or negative for a concave lens? For a convex lens? 5. Where are real images formed by a lens located? 6. Two c onvex lenses of focal length 50 cm and 5 cm are used as objective and eyepiece respectively for a simple telescope to view an object 3 meters away. When Lenses, Mirrors 32.1

Explanation / Answer

1. For a spherical mirror a distances are measured from the pole or middle point of the mirror. Distances measured along the incident ray are taken as positive while distances measured opposite to incident ray direction are taken as negative.

For a concave mirror the center of curvature C and the focus of the mirror lies in front of the mirror, so, distances R and f are measured opposite to incident ray direction and hence taken as negative. For a convex mirror the center of curvature and focus of the mirror lies backside of the mirror and hence distances R and f are measured along the incident ray. So R and f are positive for a convex mirror.

3. Real images are always formed in the same side as the object, that is, in front of the mirror.

4. By convention, the focal length of a concave lens is taken as negative and for a convex lens f is taken as positive.

5. Real images formed by a lens always form in the opposite side as the object.

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