Find the final speed of an electron

[marshall4]

Find the final speed of an electron, starting from rest, passing between two parallel plates with a potential difference of 5000V.

m=9.1*10^-31kg
q=1.6*10^-19C

v=sqr root of [2(1.6*10^-19)(5000)]/9.1*10^-31 = 4.2*10^7 m/s

Is this answer valid, why?

 

[Adrian Baker]

Yes and No

The calculation is correct and in Classical Physics all is fine. However, if you increase the PD to say 30,000V you will find the electron traveling faster than the speed of light!

Your calculation doesn't account for the mass increase of the electron as it approaches the speed of light. For most School work it is fine though.

 

[M98Ranger]

Yes, this answer is valid. The final speed of an electron can be calculated using the equation v=sqrt(2qV/m), where q is the charge of the electron, V is the potential difference, and m is the mass of the electron. Plugging in the given values for q, V, and m, we get a final speed of 4.2*10^7 m/s. This answer is valid because it follows the correct formula and uses the correct unit conversions. Additionally, the calculated speed is within a reasonable range for the speed of an electron in this scenario.