Physics Help Forum value of θ of first minimum

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 Sep 12th 2014, 10:23 AM #1 Senior Member   Join Date: Jun 2014 Posts: 306 value of θ of first minimum please refer to the photo , i am having problem with part (a) my working is d sin θ = λ sin θ = λ /d , where d is the seperation between slits.. by plug in value of λ = 580x10^-9 and d =0.7X 10^-6 , i have my θ = 47 ° , the ans given is 56° why am i wrong? Attached Thumbnails     Last edited by ling233; Sep 16th 2014 at 03:43 AM.
 Sep 16th 2014, 03:45 AM #2 Senior Member   Join Date: Jun 2014 Posts: 306 i know i shouldnt bump my own thread here. but i have posted this this sevreal days ago. yet it is not answered. i am quite disappointed. can someone try to reply?
Sep 23rd 2014, 02:13 AM   #3
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Join Date: Sep 2014
Posts: 12
Diffraction angle

 Originally Posted by ling233 please refer to the photo , i am having problem with part (a) my working is d sin θ = λ sin θ = λ /d , where d is the seperation between slits.. by plug in value of λ = 580x10^-9 and d =0.7X 10^-6 , i have my θ = 47 ° , the ans given is 56° why am i wrong?
Hi,

a) In the picture the wavelength of light is given as 580 mm. It must be 580 nm.

b) You are calculating the first maximum with the formula

sin θ = λ /d

which in general is

sin θ = m λ /d.

Giving

λ = 580x10^-9 and d =0.7X 10^-6

sin θ = 580 x 10^-9 / 0.7 x 10^-6 = 0.83 and

arcsin (0.83) = 56°.

c) I do not understand how the book gives the 16°, 34° and the 56° for the first, second and the third orders. By the way the a) part of the question does not ask the first maximum but the first minumum!
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Örsan Yüksek

Last edited by orsanyuksek; Sep 25th 2014 at 12:28 AM.

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