A thin, symmetric double-convex lens of power P is cut into three parts A, B and C as shown. Select the correct option.
A thin, symmetric double-convex lens of power P is cut into three parts A, B and C as shown. Select the correct option.
The correct option is B A is P/2
Power of a lens depends on the focal length of the refracting surfaces, which is the distance of focus from the optical centre. Focus is simply the point at which the lens is able to converge a parallel beam of rays .
For part A, the curvature of the refracting surfaces have not changed, and so has its bending ability intact. Therefore, in similar media, it would bend the rays as if the lens were as complete as the original one. Its power remains 'P'.
For parts B and C, one of the surfaces has lost its curvature, leading to a loss in the ability of the lens to bend the rays. If the rays bend less, they would converge at a point farther than the original point. So, the distance at which they converge would increase and hence the power of the lens will be reduced. As the lens is a double convex lens, by symmetry, the power of part B would be P/2.
A is P/2
Power of a lens depends on the focal length of the refracting surfaces, which is the distance of focus from the optical centre. Focus is simply the point at which the lens is able to converge a parallel beam of rays .
For part A, the curvature of the refracting surfaces have not changed, and so has its bending ability intact. Therefore, in similar media, it would bend the rays as if the lens were as complete as the original one. Its power remains 'P'.
For parts B and C, one of the surfaces has lost its curvature, leading to a loss in the ability of the lens to bend the rays. If the rays bend less, they would converge at a point farther than the original point. So, the distance at which they converge would increase and hence the power of the lens will be reduced. As the lens is a double convex lens, by symmetry, the power of part B would be P/2.
