(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

An electron in the beam of a typical television picture tube is accelerated through a potential difference of 2.0*10^4 V before it strikes the face of the tube. What is the energy of this electron, in electron volts, and what is its speed when it strikes the screen?

2. Relevant equations

delta V = delta Ep/q

Ek=0.5mv^2

3. The attempt at a solution

well, I used the first equation to find its electric potential energy, which is (2.0*10^4)*(1.6*10^-19), and that gives me 3.2*10^-15J

then since it's asking in eV, and 1eV = 1.6*10^-19J, i do (3.2*10^-15)/(1.6*10^-19), which gives me 2*10^4eV (exact number as we started).

I don't see anything wrong with the procedure but the answer is 2*10^-4eV. what did i do wrong?

as for speed: (im using my 2*10^4eV as the energy)

Ek=0.5mv^2, and energy in J is 3.2*10^-15J

so 3.2*10^-15 = 0.5 (9.11*10^-31)v^2

that gives me 8.4*10^7m/s, which is exactly the same as the answer.

therefore i'm assuming the answer key for the energy in eV is wrong, what do you think?

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: What is the energy of this electron

**Physics Forums | Science Articles, Homework Help, Discussion**