1.Blue light with a wavelength of 440 nm is used in a double slits are 0.50 mm apart. If the screen is 1.5 m from the slits, what is the angular separation of the first-order bright fringes?

Answer given is : 1.8x10^-3

2.Monochromatic light passes through two narrow slits 0.25 mm apart and forms an interference pattern on screen 1.5 m away. If light with a wavelength of 680 nm is used, what is the distance between the center of the central maximum and the center of the third-order bright fringe?

Answer given is 1.2x10^-2 m.

Can someone help me on physical optics.I'm doing my revision and I'm stuck.Help me please.Thanks

2. Use the equation:



Where x is the distance between two bright fringes,
l the distance from the slits to the screen
lambda the wavelength
d the distance between the slits.

Be sure that all your units are consistent, that is if you use metres, convert everything to metres first.

For one, I'm not getting the answer you gave, but I got after using the same formula, and using a trig ratio to get the angle.