Advertisements
Advertisements
Question
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
Solution
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.
RELATED QUESTIONS
What does sign of power (+ve or –ve) indicate?
A doctor has prescribed a corrective lens of power +1.5 D. Find the focal length of the lens. Is the prescribed lens diverging or converging?
The lens mentioned in 6(b) above is of focal length 25cm. Calculate the power of the lens.
Name the type of lens whose power is positive.
The image of an object formed by a lens is real, inverted and of the same size as the object. If the image is at a distance of 40 cm from the lens, what is the nature and power of the lens ? Draw ray diagram to justify your answer.
A normal eye is not able to see objects closer than 25 cm because
A thin converging lens is formed with one surface convex and the other plane. Does the position of image depend on whether the convex surface or the plane surface faces the object?
A double convex lens has two surfaces of equal radii R and refractive index \[m = 1 \cdot 5\]
According to Rayleigh’s scattering law, the amount of scattering of light is inversely proportional to the fourth power of its ______.
Define power of a lens. What is its unit? One student uses a lens of focal length 50 cm and another of –50 cm. What is the nature of the lens and its power used by each of them?
The focal length of a double convex lens is equal to the radius of curvature of either surface. What is the refractive index of its material?
