# Solve Physics Problem w/ Wavelength & 2 Slits - Wavelength Forums

• Kdawg
In summary, the conversation is about finding the wavelength of violet light using the equation for double-slit interference. The person asking for help has missed a day of class and is looking for advice or a website to help them understand how to solve these types of problems. A helpful website is given and the simplified equation for finding wavelength is provided, with a reminder to pay attention to units. The conversation also mentions a NASA website for double-checking the calculated value.
Kdawg
I missed a day of class the other day so I don't have any notes on how to do this. If someone could please give me some tips or a site that helps explain how to do problems like these it would be greatly appriciated.

Violet light falls on two slits separated by 1.92 10-5 m. A first-order line appears 13.1 mm from the central bright line on a screen 0.611 m from the slits. What is the wavelength of the violet light?

I have about 10 problems do tomarrow very similar to this one and not a clue how to do them.

Kdawg said:
I missed a day of class the other day so I don't have any notes on how to do this. If someone could please give me some tips or a site that helps explain how to do problems like these it would be greatly appriciated.

Violet light falls on two slits separated by 1.92 10-5 m. A first-order line appears 13.1 mm from the central bright line on a screen 0.611 m from the slits. What is the wavelength of the violet light?

I have about 10 problems do tomarrow very similar to this one and not a clue how to do them.

http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/slits.html

The reference that Older Dan gave, is very useful.. You will find that you
need to rewrite their equation to suit your data. Just be careful
of units. To find the solution for lambda in nanometers, convert your data to the units they are using. (I have shown their units in parenthesis)

e.g. lambda = [ymD]/d

y - displacement from centerline (in cm)
m - degree for order of line (1, 2, 3 etc..)
D - screen distance (in cm)
d - slit separation (in micrometers = 10^-6m)
lambda - wavelength (nm)

An http://eosweb.larc.nasa.gov/EDDOCS/Wavelengths_for_Colors.html (a double check for your calculated value) of wavelength for violet can be found by following the blue hyperlink.

Last edited by a moderator:
Reworking that equation again, I found the derived equation in my last post
was incorrect! (I'm surprised no one challenged me on that)

correction: lambda = [dy]/[mD]

y - displacement from centerline (m)
m - degree for order of line (1, 2, 3 etc..)
D - screen distance (m)
d - slit separation (m)
lambda - wavelength (m)

Again be careful of units. Just convert to those in this equation. To express lambda in nanometers, multiply the resulting lambda by 10^9.

## 1. What is the purpose of using two slits in a physics problem involving wavelength?

The use of two slits in a physics problem allows for the phenomenon of interference to occur. This creates a pattern of alternating light and dark fringes, which can be used to determine the wavelength of the light source.

## 2. How do you calculate the wavelength using two slits?

To calculate the wavelength, you can use the formula λ = dsinθ, where λ is the wavelength, d is the distance between the two slits, and θ is the angle between the center of the pattern and the first order fringe.

## 3. What is the relationship between the distance between the two slits and the resulting pattern of fringes?

The distance between the two slits is directly proportional to the distance between the fringes. As the distance between the slits increases, the distance between the fringes also increases.

## 4. Can this method be used for any type of light source?

Yes, this method can be used for any type of light source, as long as the light is coherent and monochromatic. This means that the light waves have a constant phase relationship and are all of the same wavelength.

## 5. What other factors may affect the accuracy of the calculated wavelength using this method?

Factors that may affect the accuracy of the calculated wavelength include the angle of incidence of the light, the width of the slits, and any external interference or diffraction that may occur. It is important to control these factors as much as possible to obtain an accurate result.

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