Question

One grating has 20 slits and another grating has 6000 slits. If all else is equal, which grating will be most useful in determining the chemical composition of distant stars using spectroscopy? (a) the grating with 20 slits (b) the grating with 6000 slits (c) they are both the same

Answer 1

For the spectroscopy of the distant star, we need the higher resolution grating to resolve to wavelengths. Greater resolving power means how clearly grating is resolving two closely spaced wavelengths. The resolvance or resolving power of the grating is R

R = mN , where m is the order of diffraction and N is the number of total illuminated slits.

Now given gratings, one has 20 slits in same length as other one has 6000 slits. So, grating with 6000 slits has greater resolving power.

So, grating with 6000 slits is more useful.