some physics lab questions (laser diffraction lab) 1. You have a laser with wave

Question

some physics lab questions (laser diffraction lab)

1. You have a laser with wavelength = 640.5[nm]. The grating has a slit spacing of 1.677E-03[mm]. What is the angle measured for n=1

(I used " d sin theta = m wavelength and got 0.382 in radin and got it wrong)

2.You measure a distance from diffraction to screen to be 310[mm]. What should be the angle to the first spot measured off axis, if the distance from the center spot is 1.281E+02[mm]

(I got 0.413 in radin and got it wrong)

3.

For this question your laser has a wavelength of 640.5[nm]. You measure a distance from diffraction grating to screen to be 310[mm] and the first spot is measured a distance from center axis to be 1.281E+02[mm]. How many slits per millimeter are there? answer fo the nearest integer slit.

( I used y/L=m(wavelength)/d and got 645, but it was wrong)

explain please!

thanks

Explanation / Answer

1) Given Data

wavelength = 640.5 nm = 640.5*10^-9 m

slit spacing , d =1.677E-03 mm = 1.677*10^-6 m

n = 1

dsin(theta) = n(wavelength)

1.677*10^-6 m * sin(theta) = 1*640.5*10^-9 m

theta = 22.45 deg

Angle in radians is 22.45*(Pi/180) = 0.392 radians

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2) Given Data

distance from diffraction to screen , D = 310 mm

distance from the center spot y =1.281*10^2 mm

tan (theta) = y / D

tan (theta) =1.281*10^2 / 310

theta = 22.45 degrees

Angle in radians is 22.45*(Pi/180) = 0.392 radians

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3) Given Data

wavelength = 640.5 nm = 640.5*10^-9 m = 640.5*10^-6 mm

distance from diffraction to screen , D = 310 mm

distance from the center spot y =1.281*10^2 mm

n = 1

Find the distance between lines (a diffraction grating has lines) 'd' using

dsin(theta) = n(wavelength)

tan (theta) = y / D = 1.281*10^2 / 310 = => theta = 22.45 degrees

dsin(theta) = n(wavelength)

so

d*sin(22.45) = 1*640.5*10^-6

d = 1.67724*10^-3 mm

so

Number of slits / mm =1/d = 596.22 slits/mm

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