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Two objects P and Q when placed at different positions in front of a concave mirror of focal length 20 cm, form real images of equal size. Size object P is three times size of object Q. If the distance of P is 50 cm from the mirror. Find the distance of Q from the mirror. |
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Answer» Solution :Here, F = - 20 cm `h_p = 3 h_Q ,h_p=h_Q,u_p=-50` cm and for real image v is ALSO - ve. We know that magnification `(h.)/h=(-v)/u=f/(f-u)` `:.` For OBJECT P , we have `(h.)/(h_p)=(-20)/((-20)-(-50))=(-20)/30=(-2)/3 ""...(i)` and for object Q , we have `(h.)/(h_Q)=(h.)/(h_p/3)=(3h.)/(h_p)=(-20)/((-20)-(-u_Q))=(-20)/(u_Q-20)` `implies (h.)/h_p=(-20)/(3xx(u_Q-20))=(-20)/(3u_Q-60)""...(ii)` Comparing (i) and (ii) , we get `(-2)/3=-(20)/((3u_Q-60))` `implies2(3u_Q-60)=3xx20=60` `implies |u_Q|=30 cm` |
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