Finding Color of Two Lights Given Slit Source & Screen Distance

[meher4real]

Homework Statement

How to determine the wavelength of lights without having the angle of the diffraction \theta ??

Relevant Equations

d sin \theta = m \lambda
sin \theta = m \lambda / d

Given values :
- Distance between the slit source and the screen L
- d1,d2
The problem is to detemine the color of the two lights

 

[haruspex]

Homework Statement:: How to determine the wavelength of lights without having the angle of the diffraction \theta ??
Relevant Equations:: d sin \theta = m \lambda
sin \theta = m \lambda / d

Given values :
- Distance between the slit source and the screen L
- d1,d2
The problem is to detemine the color of the two lights

Please post the whole question exactly. If it is not in English please post the original and your translation.

 

[meher4real]

Determine the wavelength of light from the diffraction at a slit width of 0.4 mm, if the diffraction pattern is observed on the screen at a distance of 2.5 m from the slit and the second minima of the given color are 10.6 mm apart. Use the tables to determine the color of the light.

 

[berkeman]

Determine the wavelength of light from the diffraction at a slit width of 0.4 mm, if the diffraction pattern is observed on the screen at a distance of 2.5 m from the slit and the second minima of the given color are 10.6 mm apart. Use the tables to determine the color of the light.

That helps. So now can you start working the problem using your Relevant Equations?

 

[meher4real]

My bad, sorry for the misunderstanding !
As i said before you need angle \theta to solve \lambda according to that equation.
Any formula that can help me solve this problem or in that case \theta must be a known value ?

 

[hutchphd]

If you make a drawing and can do trigonometry you are done.
Do you understand what the "second minimum" means?

 

[meher4real]

Maybe in french i would understand it.
What does it mean ?

 

[hutchphd]

I fear this is a physics understanding problem not a language problem. What does "theta" "lambda" "m" and "d" mean in the equations you wrote down?

 

[meher4real]

With all respect but some scientific terms are different in English if you know what i mean.
λ Wavelength
θ between the path and a line from the slits to the screen
d is the distance between the slits
m = 0, 1, −1, 2, −2, . . . (constructive)
Even with this equation can't get it !
ym = m λ L / d

 

[meher4real]

Wait, can i use L = d sinθ or θ =d/L

 

[hutchphd]

No, but you're getting there. You can use the L and the data about the position of the second minimum to find theta. Knowing it is the second minimum allows use of the equation relating d and $\lambda$ to the diffraction geometry

 

[meher4real]

No, but you're getting there. You can use the L and the data about the position of the second minimum to find theta. Knowing it is the second minimum allows use of the equation relating d and $\lambda$ to the diffraction geometry
View attachment 284129

Thank you for your response but first i would like to verify some values.
From the problem above we get :
L=2.5m d=10.6mm and "a" (slit width) = 0.4mm
L>>d so tanθ =y/L
is y same as d ?
How to use m in the equation every value got his own angle θ for 0,1,2 ?
If "a" is right when to use it ? In what equation ?
I'm lost here
Please help me i want to know the concept.

 

[hutchphd]

Sorry I have lost your definitions. d is usually the slit width. "y" is the off axis distance on the detector so your equation for tan (theta) seems ok.

 

[meher4real]

Then how to calculte "y" if λ isn't available ?
y= m λ L / d

 

[haruspex]

Then how to calculte "y" if λ isn't available ?
y= m λ L / d

You are given the information for $y_m$:

the second minima of the given color are 10.6 mm apart

You need to figure out what values of m correspond to the second minima.

 

[meher4real]

Thank you for your time, your responses means a lot guys because today is the deadline.
I need to send my homeworks today. Only 2 problems left and i need to solve this one asap.
I know nothing about Optic, i do my best studying it but still not enough.
Is "ym" same as "d" ?
Is second minima means m=2 ?

 

[haruspex]

Thank you for your time, your responses means a lot guys because today is the deadline.
I need to send my homeworks today. Only 2 problems left and i need to solve this one asap.
I know nothing about Optic, i do my best studying it but still not enough.
Is "ym" same as "d" ?
Is second minima means m=2 ?

d is the width of the slit. $y_m$ is displacement from the centre of the diffraction pattern to the $m^{th}$ minimum, so the second minima are at m=2 and m=-2.

 

[meher4real]

Hi !
What's the value q of photon ? please help ? i need to figure the voltage.
q photon = ?

 

[haruspex]

Hi !
What's the value q of photon ? please help ? i need to figure the voltage.
q photon = ?

q? Sounds like a charge. Photons don't have charge, none of your equations have a variable called q, and I see no mention of voltage in the thread. What voltage?