# Solving Diffraction Problem with Angle of Deviation & Second Order

• Jchem
In summary, the conversation is discussing the use of the Diffraction grating equation to calculate the number of lines per cm on a diffraction grating. The concept of second order and the angle of deviation of light are also mentioned. The "order" refers to which dot or fringe of light is being observed.
Jchem
I have no idea where to start here..

this is the only question in this unit that has an angle in it... also not sure what second order means.

the angle of deviation of light of 400 nm wavelength is 30 degrees in second order. How many lines per cm are there on this diffraction grating if N = 1/d

any tips on how to get started?

thanks

You want the Diffraction grating equation:

n*lamda = d sin(theta)

n = 2 (in your case) as it is second order.
lamda = wavelength
d = spacing on diffraction grating

THe "order" is referring to which "dot" or "fringe" of light you are looking at. When a beam shines through a diffraction grating, the dot that appears along the straight line path from the beam is the "central" or "zeroth" order. The closest dots on either side of the central dot are called "first order," and the next are called second, third, etc.

## 1. What is diffraction and why is it important to study?

Diffraction is a phenomenon that occurs when waves, such as light or sound, encounter an obstacle or pass through a narrow opening. It causes the waves to spread out and interfere with each other, creating patterns of light and dark. Studying diffraction allows us to understand and control how waves behave, which is crucial in fields such as optics, acoustics, and telecommunications.

## 2. What is the angle of deviation in diffraction?

The angle of deviation is the angle between the incident wave and the direction of the diffracted wave. It is measured from the center of the diffraction pattern to the first minimum or maximum of the interference pattern.

## 3. How is the angle of deviation related to the wavelength of the incident wave?

The angle of deviation is directly proportional to the wavelength of the incident wave. This means that as the wavelength increases, the angle of deviation also increases.

## 4. What is second order diffraction and how does it differ from first order diffraction?

Second order diffraction occurs when the diffracted wave is two wavelengths away from the incident wave, while first order diffraction occurs when the diffracted wave is one wavelength away. This means that the angle of deviation for second order diffraction is twice as large as that of first order diffraction.

## 5. How can the angle of deviation and second order diffraction be used to solve diffraction problems?

By knowing the angle of deviation and the order of diffraction, we can use the diffraction equation to calculate the wavelength of the incident wave or the size of the diffracting opening. This information is useful in designing and optimizing diffraction-based devices and systems.

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