White light containing wavelengths from 405 nm to 760 nm falls on a grating with 7510 lines/ cm. How wide is the first-order spectrum on a screen 2.29 m away?(adsbygoogle = window.adsbygoogle || []).push({});

I'm not sure the way this question is worked out, but what I have so far is

sin(theta)=[m*Lambda+ m*Lambda]/d

d=1/7510cm=1.33e-6m

sin(theta)=[(407e-9m)+(705e-9m)]/1.33e-6m= 0.876 theta=61 degrees

width=2x(tan theta)=(2*2.29)*(tan 61)=8.32m

I have the wrong answer so I must have done something wrong. Can someone help?

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# Diffraction grating of white light

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