Advertisements
Advertisements
प्रश्न
How does focal length of a lens change when red light incident on it is replaced by violet light? Give reason for your answer.
Advertisements
उत्तर
The refractive index of the material of a lens increases with the decrease in wavelength of the incident light. So, focal length will decrease with decrease in wavelength according to formula.
`1/f = (mu - 1)(1/R_1 - 1/R_2)`
Thus, when we replace red light with a violet wavelength decrease and hence the focal length of the lens also decrease.
संबंधित प्रश्न
A convex lens forms a real and inverted image of a needle at a distance of 50 cm from it. Where is the needle placed in front of the convex lens if the image is equal to the size of the object? Also, find the power of the lens.
(a) At what distance should the lens be held from the figure in order to view the squares distinctly with the maximum possible magnifying power?
(b) What is the magnification in this case?
(c) Is the magnification equal to the magnifying power in this case? Explain.
Which type of lens has (a) a positive power, and (b) a negative power?
A diverging lens has focal length of 3 cm. Calculate the power.
An object of height 4 cm is placed at a distance of 15 cm in front of a concave lens of power, −10 dioptres. Find the size of the image.
A diverging lens has a focal length of 0.10 m. The power of this lens will be:
A convex lens is of focal length 20 cm. Find its power.
The power of lens depends on the focal length of the lens
An object is placed in front of a converging lens. Obtain the conditions under which the magnification produced by the lens is
- negative and
- positive.
A point object is placed at O in front of a glass sphere as shown in figure.
Show the formation of the image by the sphere.
