MC - Physics

A: mλ = dsinθ, sinθ = mλ/d

For the fringes are observable, sinθ < 1,

so, λ/d < 1 for m = 1

Hence, λ must be smaller than d for any fringes to be seen, this is correct.


B: Fringe separation, x = λD / d. So, when d decreases, the fringes separation will be larger, they will move further apart. This is correct.


C: mλ = dsinθ <= d, m <= d/λ

For more fringes to be seen, a smaller λ light should be used. This is correct.


D: If the screen is moved back, the fringe separation will be larger, but there is no effect on the number of fringes formed. So, this is wrong.


E: After the light being diffracted by the slits, the light is enclosed in the diffraction envelope. So, the fringes lessen in brightness away from the central maximum. This is correct.


F: The light must be coherent for any stable interference to be seen, that's why we use the double slits. This is correct.


G: We can account for the fringes by Huygen's principle and also principle of interference, in which it is also a principle of superposition. So, this is right.