282466 The focal length in air of a thin lens made of glass of refractive index 1.5 is \(L\) when immersed in water (refractive index \(=4 / 3\) ), its focal length becomes

282457 Two thin lenses have a combined power of +9 D. When they are separated by a distance of 20 \(\mathrm{cm}\), their equivalent power becomes \(+\frac{27}{5} \mathrm{D}\), then their individual powers are

282458 A light beam parallel to axis is incident on the system of four convex lenses \(A, B, C\) and \(D\). Focal lengths of \(A, B, C\) and \(D\) are \(30 \mathrm{~cm}, 10\) \(\mathrm{cm}, 30 \mathrm{~cm}\) and \(10 \mathrm{~cm}\), respectively as shown. Here, fixed distance \(B C=20 \mathrm{~cm}\). What should be the distance between the lens \(A\) and lens \(D\) so that after refractions, rays will be parallel to axis in regions I, III and V?

282459 The distance between a convex lens and a plane mirror is \(10 \mathrm{~cm}\). The parallel rays incident on the convex lens, after reflection from the mirror, form image at the optical centre of the lens. Then the focal length of the lens is

282466 The focal length in air of a thin lens made of glass of refractive index 1.5 is \(L\) when immersed in water (refractive index \(=4 / 3\) ), its focal length becomes

282457 Two thin lenses have a combined power of +9 D. When they are separated by a distance of 20 \(\mathrm{cm}\), their equivalent power becomes \(+\frac{27}{5} \mathrm{D}\), then their individual powers are

282458 A light beam parallel to axis is incident on the system of four convex lenses \(A, B, C\) and \(D\). Focal lengths of \(A, B, C\) and \(D\) are \(30 \mathrm{~cm}, 10\) \(\mathrm{cm}, 30 \mathrm{~cm}\) and \(10 \mathrm{~cm}\), respectively as shown. Here, fixed distance \(B C=20 \mathrm{~cm}\). What should be the distance between the lens \(A\) and lens \(D\) so that after refractions, rays will be parallel to axis in regions I, III and V?

282459 The distance between a convex lens and a plane mirror is \(10 \mathrm{~cm}\). The parallel rays incident on the convex lens, after reflection from the mirror, form image at the optical centre of the lens. Then the focal length of the lens is

282466 The focal length in air of a thin lens made of glass of refractive index 1.5 is \(L\) when immersed in water (refractive index \(=4 / 3\) ), its focal length becomes

282457 Two thin lenses have a combined power of +9 D. When they are separated by a distance of 20 \(\mathrm{cm}\), their equivalent power becomes \(+\frac{27}{5} \mathrm{D}\), then their individual powers are

282458 A light beam parallel to axis is incident on the system of four convex lenses \(A, B, C\) and \(D\). Focal lengths of \(A, B, C\) and \(D\) are \(30 \mathrm{~cm}, 10\) \(\mathrm{cm}, 30 \mathrm{~cm}\) and \(10 \mathrm{~cm}\), respectively as shown. Here, fixed distance \(B C=20 \mathrm{~cm}\). What should be the distance between the lens \(A\) and lens \(D\) so that after refractions, rays will be parallel to axis in regions I, III and V?

282459 The distance between a convex lens and a plane mirror is \(10 \mathrm{~cm}\). The parallel rays incident on the convex lens, after reflection from the mirror, form image at the optical centre of the lens. Then the focal length of the lens is

282466 The focal length in air of a thin lens made of glass of refractive index 1.5 is \(L\) when immersed in water (refractive index \(=4 / 3\) ), its focal length becomes

282457 Two thin lenses have a combined power of +9 D. When they are separated by a distance of 20 \(\mathrm{cm}\), their equivalent power becomes \(+\frac{27}{5} \mathrm{D}\), then their individual powers are

282458 A light beam parallel to axis is incident on the system of four convex lenses \(A, B, C\) and \(D\). Focal lengths of \(A, B, C\) and \(D\) are \(30 \mathrm{~cm}, 10\) \(\mathrm{cm}, 30 \mathrm{~cm}\) and \(10 \mathrm{~cm}\), respectively as shown. Here, fixed distance \(B C=20 \mathrm{~cm}\). What should be the distance between the lens \(A\) and lens \(D\) so that after refractions, rays will be parallel to axis in regions I, III and V?

282459 The distance between a convex lens and a plane mirror is \(10 \mathrm{~cm}\). The parallel rays incident on the convex lens, after reflection from the mirror, form image at the optical centre of the lens. Then the focal length of the lens is