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A 4.5 cm needle is placed 12 cm away from a convex mirror of focal length 15 cm. Give the location of the image and the magnification. Describe what happens as the needle is moved farther from the mirror. |
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Answer» SOLUTION :Here, `f=4.5 cm, u=-12 cm` and f= + 15 cm, hence as per MIRROR formula `1/v+ 1/u = 1/f`, we have `1/v =1/f -1/u =1/(+15) =1/15 + 1/12 = (4+5)/60 = 9/60 = 3/20 rArr v=+20/3 cm = + 6.7 cm` Again, `m=h^(.)/h =-v/u`, hence, `h. =-v/u xx h =-(6.7)/(-12) xx 4.5 = +2.5 cm` and magnification `m=h^(.)/h = (2.5 cm)/(4.5 cm) = 0.55` As the needle is MOVED farther from the mirror, the image moves from the side of pole towards (but NEVER beyond) the principal focus of the mirror. Moreover, magnification `m to 0` |
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