Calculating de Broglie Wavelength & Double-Slit Fringe Width

[v_pino]

Homework Statement

Find the de Broglie wavelength for an electron with v=0.001c. Find the angular width of the central bright fringe in a double slit experiment, with the separation of the two slits d=50nm.

Homework Equations

wavelength = h/mv

d sin(theta)=n*wavelength

The Attempt at a Solution

For the wavelength, I got 2.42x10^-9m. I think this sounds correct.

Is my second equation for diffraction applicable here? I know that it is double slits so there will be interference and not just diffraction. If this equation is applicable, the my answer is 2*theta = 5.55 degrees.

Or is there a specific equation for double slit that I should use?

 

[vela]

How can you calculate anything about diffraction without knowing the slit size?

 

[v_pino]

So does it mean that the question is just asking for the angle to the first maximum as in that of a diffraction pattern using dsin(theta) = n*wavelength?

 

[vela]

Not exactly. You want to find the angle between the first-order minima, since they border the central maximum.

 

[v_pino]

Sorry for not understanding the simplest of the idea here. So are you saying that the diffraction equation can be used in the question even though it is asking for interference? If so, the answer should simply be 2*theta with theta being from the equation d*sin(theta)=n*wavelength?

 

[vela]

Where did I say to use the diffraction equation?

 

[v_pino]

I don't get where you are trying to lead me here. Am I missing a big clue? Should I be using some sort of approximations? Plus I don't know the distance from screen to source - should I be estimating this?

 

[vela]

What does "angular width of the central bright fringe" mean?