Advertisements
Advertisements
प्रश्न
Will the focal length of a lens for red light be more, same or less than that for blue light?
Advertisements
उत्तर
The refractive index depends on colour of light or wavelength of light.
Cauchy's equation: `mu = A+ B/lambda^2 + C/lambda^4 + ...`
As λred > λblue hence μred < μblue
Hence parallel beams of light incident on alens will be bent more towards the axis for blue light compared to red.
By lens maker's formula,
`1/f = (mu - 1)(1/R_1 - 1/R_2)`
The refractive index for red light is less than that for blue light μred < μblue
Hence `1/f_("red") < 1/f_("blue") ⇒ f_("red") > f_("blue")`
Thus, the focal length for red light will be greater than that for blue light.
APPEARS IN
संबंधित प्रश्न
A 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 convex lens of focal length 20 cm, and
- a concave lens of focal length 16 cm?
An object 1.5 cm in size is placed on the side of the convex lens in the arrangement (a) above. The distance between the object and the convex lens is 40 cm. Determine the magnification produced by the two-lens system, and the size of the image
Two concave lenses L1 and L2 are kept in contact with each other. If the space between the two lenses is filled with a material of smaller refractive index, the magnitude of the focal length of the combination
A convex lens forms a real image of a point object placed on its principals axis. If the upper half of the lens is painted black,
(a) the image will be shifted downward
(b) the image will be shifted upward
(c) the image will not be shifted
(d) the intensity of the image will decrease.
A small piece of wood is floating on the surface of a 2.5 m deep lake. Where does the shadow form on the bottom when the sum is just setting? Refractive index of water = 4/3.
An unsymmetrical double convex thin lens forms the image of a point object on its axis. Will the position of the image change if the lens is reversed?
A plano convex lens has diameter of 10 cm and its thickness at the centre is 0.5 cm. Speed of light in the lens is 2 × 108 ms-1. What is the focal length of the lens?
In the given figure the radius of curvature of the curved face in the planoconvex and the planoconcave lens is 15 cm each. The refractive index of the material of the lenses is 1.5. Find the final position of the image formed.
The point on the principal axis where rays parallel to the principal axis actually meet after refraction, or appear to diverge after refraction, is called the:
In the Lens Maker's Formula, the symbols \[R_1\] and \[R_2\] denote:
Which of the following is the correct Thin Lens Formula?
For a thin lens, the magnification \[m\] in terms of image distance \[v\] and object distance \[u\] is given by:
According to the new Cartesian sign convention for lenses, the focal length of a convex lens is:
According to the new Cartesian sign convention for lenses, the focal length of a concave lens is:
A ray parallel to the principal axis, after refraction through a convex lens, passes through:
A ray passing through the principal focus of a convex lens, after refraction, emerges:
Using the sign convention with \[OB = -u\] and \[DI = +v\] in the combined refraction equation for a thin lens gives:
Magnification produced by a lens is positive when the image is:
