Advertisements
Advertisements
प्रश्न
Answer the following question.
Three lenses of focal length +10 cm, —10 cm and +30 cm are arranged coaxially as in the figure given below. Find the position of the final image formed by the combination.
उत्तर
`1/v - 1/u = 1/f`
`u = -30 cm`
`f = +10 cm`
`1/nu = 1/f + 1/u`
`1/nu_1 = 1/10 - 1/30`
⇒ `1/nu_1 = (3 - 1)/30 = 2/30`
`nu_1 = 15` cm
`u = +10 cm`
`f = -10 cm`
`1/nu_2 = 1/f + 1/u = 1/10 - 1/10`
`nu_2 = ∞`
For third lens object is at infinity hence image is formed at focus final image at a distance of 30 cm.
संबंधित प्रश्न
If an object far away from a convex mirror moves towards the mirror, the image also moves. Does it move faster, slower or at the same speed as compared to the object?
A U-shaped wire is placed before a concave mirror having radius of curvature 20 cm as shown in figure. Find the total length of the image.
A narrow pencil of parallel light is incident normally on a solid transparent sphere of radius r. What should be the refractive index is the pencil is to be focussed (a) at the surface of the sphere, (b) at the centre of the sphere.
A converging lens and a diverging mirror are placed at a separation of 15 cm. The focal length of the lens is 25 cm and that of the mirror is 40 cm. Where should a point source be placed between the lens and the mirror so that the light, after getting reflected by the mirror and then getting transmitted by the lens, comes out parallel to the principal axis?
According to Cartesian sign convention, all distances are measured from the _______.
According to the mirror equation, ______.
A thin converging lens of focal length 12 cm is kept in contact with a thin diverging lens of focal length 18 cm. Calculate the effective/equivalent focal length of the combination.
The focal length of a convex lens made of glass of refractive index (1.5) is 20 cm.
What will be its new focal length when placed in a medium of refractive index 1.25?
Is focal length positive or negative? What does it signify?
A short object of length L is placed along the principal axis of a concave mirror away from focus. The object distance is u. If the mirror has a focal length f, what will be the length of the image? You may take L << |v – f|.
A concave mirror of focal length 12 cm forms three times the magnified virtual image of an object. Find the distance of the object from the mirror.
