Value of theta of first minimum

AI Thread Summary
The discussion centers on a homework problem involving a diffraction grating with a wavelength of 580 nm and a slit separation of 0.7 μm. The initial calculations for the angle θ using the formula d sin θ = λ led to an incorrect result of 47°, while the expected answer is 56°. The confusion arose from a misunderstanding of the slit separation value, which was clarified to be 0.7 μm, not 70 μm. Additionally, it was noted that part (a) of the problem pertains to a single slit rather than multiple slits. Accurate interpretation of the parameters is crucial for solving diffraction problems correctly.
desmond iking
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Homework Statement


A parallel beam of monochromatic light of wavelength 580nm is incidentally normal on a diffraction grating. The separation between successive lines on the grating is 0.7μm as shown in the figure.
please refer to the photo , i am having problem with part (a)


Homework Equations





The Attempt at a Solution


my working is d sin θ = λ
sin θ = λ /d , where d is the separation between slits.. by plug in value of λ = 580x10^-9 and d = 1/ (5000x10^2) , i have my θ = 47 ° , the ans given is 56°
why am i wrong?
 

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Where are you given that value for d?
 
Last edited:
NascentOxygen said:
Where are you given that value for d?

sorry i made a typo.
here's what i mean :
sin θ = λ /d , where d is the separation between slits.. by plug in value of λ = 580x10^-9 and d = 0.7x10^-6 , i have my θ = 47 ° , the ans given is 56°
 
Part a asks about a single slit !
And the distance between slits is NOT 70 micrometer.
 
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