# Physics

posted by .

The refractive index of a material is different for different wavelengths and colours of light. For most materials in the visible range of the electromagnetic spectrum, shorter wavelengths have larger refractive index compared to longer wavelengths.

The effect of this on lenses is that different colours from one object will be focused at different distances and thus it is impossible to have the whole object completely focused. This is known as chromatic aberration.

Dense flint is a refractive material for which the shortest wavelength of the visible spectrum at violet-blue (400 nm) has a refractive index of 1.80, while for the longest wavelength of the visible spectrum at red (800 nm) has a refractive index of 1.70

Consider a converging lens made out of dense flint with R1=10 cm and R2=-10 cm.

We place a white object at a distance of 108 cm from the lens. Since white light is composed of all visible colours, when it passes through the lens, the different colours will form images at different distances.

What is distance between the red image of the object and the blue-violet image?

• Physics -

The lens focal length is inversely proportional to n-1. Thus
f(blue)/f(red) = 7/8 = 0.875

The focal length at any particular wavelength can be calculated using the "lens maker's formula" whch you can find at

http://scienceworld.wolfram.com/physics/LensMakersFormula.html

In your case, for "white" light with n = 1.75 (a red-blue average),
1/f = (0.75)(1/10 + 1/10) = 0.15
f(white)= 6.67 cm
f(blue) = 5/0.8 = 6.25 cm
f(red) = 5/0.7 = 7.14 cm

Use the standard lens equation
1/f = 1/do + 1/di
to compute the difference in the image distances, di. Use do = 108 cm

• Physics -

how did u get that do=108cm?

• Physics -

oh nevermind i got it

• Physics -

sorry, another question. what would f be in the len makers equation?

## Similar Questions

1. ### Physics - EM spectrum

Here's the question: which part of the electromagnetic spectrum has a refractive index of 1.45 in glass?
2. ### Physical Science

These are two questions that I need help with: 1.What statement about light traveling through water and glass is true?
3. ### Science

D. _____ has wavelengths between 0.7 and 0.4 millionths of a meter. D1. What you see as different colors are electromagnetic waves of different ______. D2. Red ligh has the _____ wavelengths (lowest frequency); blue light has the _____ …
4. ### Physics

The refractive index of a medium changes with the wavelength of incident light. Typically, the shorter the wavelength the larger the refractive index. Fused quartz has a refractive index of 1.47 for indigo light of 400 nm in wavelength, …
5. ### Algebra Assignment

Please check my work on this part of the assignment. Medical x-rays, with a wavelength of about 10^-10m, can penetrate completely through your skin. a. ultraviolet rays, which cause sun burn by penetrating only the top level of skin, …
6. ### Physics. URGENT Help Please

What is the separation of colors in a rainbow produced by?
7. ### PHYSICS

Imagine a soap film (air-soapy water-air) of 1 l,m thickness, and refractive index of 1.5 with white light normal to the film. Which wavelengths in the optical range (400 nm to 700 nm) will appear brightest?
8. ### Physical Science

QUESTION---Which waves have wavelengths longer than those of visible light?
9. ### physics

When you look through a 3.7 mm thick window comprised of a material whose refractive index is 1.59, by what time interval is the light you see delayed by having to go through glass instead of air?
10. ### physics

When you look through a 3.7 mm thick window comprised of a material whose refractive index is 1.59, by what time interval is the light you see delayed by having to go through glass instead of air?

More Similar Questions