beam of light converges at a point P. Now a lens is placed in the path of the convergent beam 12 cm from P. At what point does the beam converge if the lens is
(a) a convex lens of focal length 20 cm, and
(b) a concave lens of focal length 16 cm?
Asked by polyrelation | 19th Mar, 2019, 08:29: PM
Object distance, u = +12 cm (virtual object) (a) Focal length of the convex lens, f = 20 cm Image distance = v Applying lens formula 1/v – 1/u = 1/f 1/v = 1/u+ 1/f 1/v = 1/12 + 1/20 Therefore putting the values and solving the equation, we get v = 60/8 i.e. = 7.5 cm Hence, the image is formed 7.5 cm away from the lens, toward its right.(b) Focal length of the concave lens, f = -16 again image distance = v Using lens formula 1/v - 1/u = 1/f 1/v = 1/u + 1/f 1/v = 1/12 -1/16 the again as previous, applying the lens formula, substituing the values of u and f, we get v= 48 cm. Hence, the image is formed 48 cm away from the lens, towards its right.
Answered by Ankit K | 19th Mar, 2019, 11:05: PM
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