Electrons are incident on a crystal

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The discussion centers on calculating the kinetic energy required for electrons to achieve at least four diffraction maxima when incident on a crystal with a spacing of d=0.074 nm. The relevant equations include nλ=2dsinθ, P=h/λ, and K=P²/2m, where n=4 represents the order of diffraction. The expected result is a kinetic energy of 1100.0 eV. The challenge arises from the lack of a specified angle θ, prompting a need for alternative equations to determine the wavelength λ based on the electron's momentum.

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Q: Electrons are incident on a crystal which can be thought of as a series of reflecting planes with spacing d=0.074nm. What Kinetic Energy should the electrons be given in order that at least four diffracton maxima are observable?

Attempt:
The equations i think i have to use are nλ=2dsinθ, P=h/λ and then K=P^2/2m (m being mass of the electron) and form the question n=4.

i'm supposed to get an answer of 1100.0eV.

my problem is that i can't work out λ as I'm not given the angle θ, is there another set of equations i should be using? how do i get about this?

thanks aidan.
 
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The wavelength of the electron ( or anything else ) depends on it's momentum, wavelength = h/momentum.

If you look at wikipedia for electron diffraction the equations are derived for momentum in terms of accelerating voltage.
 

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