# Calculating Electric Potenial Difference

## Homework Statement

In a TV tube, an electric potential difference accelerates electrons from a rest position towards a screen. Just before striking the screen, the electrons have a wavelength of 1.0 x10-11m. Find the electric potential difference.[/B]

λ = h/mv

Ek = qΔV

## The Attempt at a Solution

[/B]
First, determine the velocity

λ = h/mv

v = h/λm

v = 6.63 x10-34J / (1.0 x10-11m)(9.11 x10-31m/s)

v = 7.28 x10-7

Now determine the electric potential difference

Ek = qΔV

1/2 mv2 = eΔV

V = 1/2 mv2 /eΔ

V = 1/2 (9.11 x10-31kg)(7.28 x10-7m/s)2 / (1.60 x10-19C)

V = 1.51 x10-24

The electric potential difference is 1.51 x10-24 V right before the electron strikes the screen.

I am fairly confident in my methods/answer but I haven't had to calculate the electric potential difference before so I just want to make sure I have the right idea. Any feedback would be great.

## Answers and Replies

Charles Link
Homework Helper
Gold Member
For the velocity, you put an extra minus sign in the exponent. It should be +7. Otherwise, your methodology is correct.

• chef99
For the velocity, you put an extra minus sign in the exponent. It should be +7. Otherwise, your methodology is correct.
Oh wow, thank you for catching that.

So the electric potential difference is actually 1.51 x10-4

Charles Link
Homework Helper
Gold Member
Oh wow, thank you for catching that.

So the electric potential difference is actually 1.51 x10-4
Try the arithmetic again. I get ## V=1.51 \cdot 10^{+4} ## volts.

• chef99