Advertisements
Advertisements
प्रश्न
A convex lens of focal length 25 cm is placed coaxially in contact with a concave lens of focal length 20 cm. Determine the power of the combination. Will the system be converging or diverging in nature?
उत्तर
We have focal length of convex lens,
`f_1 = +25 cm = +0.25 m`and focal lenghth of conceave
lens, f2 =-20 cm =-0.20 m
Equivalent focal length, `f= 1/f_1 +1/f_2 =1/25 +1/-20=-1/100`
∴ F =- 100 cm
Power of convex lens, `P_1 = 1/f_1 = 1/0.25`
Power of convex lens,`P_2 = 1/f_2 = 1/- 0.20`
Power of the combination,
`P = P_1+P_2 = 1/0.25 + 1/-0.20 = 100/25 +100/-20 = (400 - 500)/100 = (-100)/100 = -1D`
The focal length of the combination =–1 m = –100 cm.
As the focal length is in negative, the system will be diverging in nature.
APPEARS IN
संबंधित प्रश्न
An object is placed 15 cm in front of a convex lens of focal length 10 cm. Find the nature and position of the image formed. Where should a concave mirror of radius of curvature 20 cm be placed so that the final image is formed at the position of the object itself?
Suppose the lower half of the concave mirror's reflecting surface is covered with an opaque material. What effect this will have on the image of the object? Explain
A convex lens of focal length 20 cm is placed coaxially with a concave mirror of focal length 10 cm at a distance of 50 cm apart from each other. A beam of light coming parallel to the principal axis is incident on the convex lens. Find the position of the final image formed by this combination. Draw the ray diagram showing the formation of the image
Obtain the mirror formula and write the expression for the linear magnification.
An object AB is kept in front of a concave mirror as shown in the figure.
(i) Complete the ray diagram showing the image formation of the object.
(ii) How will the position and intensity of the image be affected if the lower half of the mirror’s reflecting surface is painted black?
Find the diameter of the image of the moon formed by a spherical concave mirror of focal length 7.6 m. The diameter of the moon is 3450 km and the distance between the earth and the moon is 3.8 × 105 km.
The convex surface of a thin concavo-convex lens of glass of refractive index 1.5 has a radius of curvature 20 cm. The concave surface has a radius of curvature 60 cm. The convex side is silvered and placed on a horizontal surface as shown in figure. (a) Where should a pin be placed on the axis so that its image is formed at the same place? (b) If the concave part is filled with water (μ = 4/3), find the distance through which the pin should be moved so that the image of the pin again coincides with the pin.
A mass m = 50 g is dropped on a vertical spring of spring constant 500 N m−1 from a height h = 10 cm as shown in figure. The mass sticks to the spring and executes simple harmonic oscillations after that. A concave mirror of focal length 12 cm facing the mass is fixed with its principal axis coinciding with the line of motion of the mass, its pole being at a distance of 30 cm from the free end of the spring. Find the length in which the image of the mass oscillates.
Two concave mirrors of equal radii of curvature R are fixed on a stand facing opposite directions. The whole system has a mass m and is kept on a frictionless horizontal table following figure. Two blocks A and B, each of mass m, are placed on the two sides of the stand. At t = 0, the separation between A and the mirrors is 2 R and also the separation between B and the mirrors is 2 R. The block B moves towards the mirror at a speed v. All collisions which take place are elastic. Taking the original position of the mirrors-stand system to be x = 0 and X-axis along AB, find the position of the images of A and B at t = (a) `R/v` (b) `3R/v` (c) `5R/v`.
In the case of a concave mirror of focal length f , when an object is kept between f and 2 f , show that its image is formed beyond 2 f .
