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Sri asked in Science & MathematicsPhysics · 3 months ago

Homework question. Can someone help with the answer and its "Explanation"?

Red light, of wavelength 600 nm, passes through a double slit. A pattern appears on a screen 3.0 m away. What is the distance between the 1st and 4th nodal lines, of the slits are 4.0 x 10-5 m apart? 

Update:

Can anyone give a clear answer? 

d*q_n.....n*wl....these formulas are not common (google search doesn't help me with these formula's). Can anyone give a clear answer with commonly used formulas?

1 Answer

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  • 3 months ago
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    The bright fringes appear at

    d*q_n = n*wl  n = 0 ,1, 2, 3 ...

    q_n = angle nth fringe makes with optical axis

    d = distance to betwen slits

    wl = wavelength of light

    let y_n = position of the nth bright spot on a screen D meters away.  Then

    y_n = D*q_n = n*wl*D/d

    Distance between two fringes, m and n, on the screen is

    Y_mn = |y_m - y_n| = |m - n|*D*wl/d  --> the | | are used so if n > m you get a positive number

    Set m = 4, n = 1, d = 4x10^-5m and wl = 600 nm.  For ease of computing

    d = 40 um and wl = 0.6um  then for D = 3m

    Y_14 = 3*0.6/40 = 0.045 m

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