(i) 4-5 needle is palced 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. (ii) What kind of the mirror is used in a solar furnace? Give reason for using this mirror. (iii) One half of a convex lens is covered with a black paper. Will this lens produce a complete image ofthe object? Justify your answer.

(i) 4-5 needle is palced 12 cm away from a convex mirror of focal leng

1.	(i) 4-5 needle is palced 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. (ii) What kind of the mirror is used in a solar furnace? Give reason for using this mirror. (iii) One half of a convex lens is covered with a black paper. Will this lens produce a complete image ofthe object? Justify your answer.
Answer» Solution :(i) `u=-12cm` `f=+15cm` Using mirror FORMULA `1/f=1/u+1/vimplies1/v=1/f-1/u` `implies1/v=1/15-1/(-12)` `impliesv=60/9=6.7cm` Magnification `m=(-v)/u=(h_(2))/(h_(1))` `=(-6.7)/(-12)=0.558` `m=(h_(2))/(h_(1))` `h_(2)=h_(1)xxm` `h_(2)=0.558xx4.5` `h_(2)=2.5cm` As the needle is moved farther from the mirror, image moves to the focus and size of image goes on decreasing. (ii) CONCAVE mirrors are used in solar furnaces as they CONCENTRATE solar energy in the focal plane and help in attaining high temperatures. (III) When one half of a convex lens is covered with a black paper, the lens will produce a complete image of the OBJECT but the intensity of the image is reduced because rays from the top portion of the lens only are refracted and forms the image.