1.

A concave mirror and convex lens (both of refractive index 1.5) have focal length 3 cm in air. When they are placed in water ofrefractive index 4/3, then their new focal lengths will be ......

Answer»

`f_("lens")`=12 cm ,`f_("MIRROR")`=3 cm
`f_("lens")`=3 cm ,`f_("mirror")`=12 cm
`f_("lens")`=3 cm ,`f_("mirror")`=3 cm
`f_("lens")`=12 cm ,`f_("mirror")`=12 cm

Solution :New FOCAL length of CONVEX lens = `4 xx 3 = 12` cm When concave mirror is kept in water then its focal length remains UNCHANGED hence new focal length = 3 cm.


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