Why did they use these formulas for energy of electron.

[cloudage]

Homework Statement

An electron microscope employs a beam of electrons to obtain an image of an object. What energy must be imparted to each electron of the beam to obtain a wavelength of 10.0pm?

Homework Equations

1. E = hv=hc/lambda
2. lambda = h/(mv)
3. KE = .5mv^2

The Attempt at a Solution

In this problem I thought you could use the first equation to find the energy with the specific wavelength of 10pm. However, the workbook goes through equations 2 and 3 to first find the velocity and then find the kinetic energy. The answers come out very different, so I must be thinking wrong. Can anyone help me understand this?
Since I am solving for energy, why do I need to go through equations 2 and 3?

 

[Doc Al]

1. E = hv=hc/lambda

This only applies to photons.

2. lambda = h/(mv)
3. KE = .5mv^2

For an electron, you'll need these two equations.

 

[cloudage]

So whenever they say "electrons" I need to use them? That makes sense, I figured the electrons were being emitted as photons so I thought of them as photons.

Thank you for your help, I see why I got the wrong answer on a couple of other problems now too

 

[Doc Al]

So whenever they say "electrons" I need to use them?

For any kind of massive particle. (A photon has no mass.)

That makes sense, I figured the electrons were being emitted as photons so I thought of them as photons.

Yikes, don't do that.