Electric Field Force and Charge to Mas Ratio (1 Viewer)

[wrxsti]

could someone please tell me the formula for electric field FORCE....... it not on the formula sheet .... and can someone show me how to calculate the chareg to mass ratio of an electron

Thanks... Physics trial is 2moz so if i can get a speedy reply

 

[shredinator]

F = qE -------------- Electric Force
F = qvB ------------- Magnetic Force

Thompson made it so that these forces cancelled out.. Ie:

qE = qvB

which gives v = E/B

now qvB = mv^2/r (centripetal force, because the magnetic field causes the electrons curve up in a circle )

this rearranges to:

q/m = v/Br

You wont' have to talk about actual values - just explain thats how he arrived. From here Thompson subbed in v (which equals E/B from before), B and r to get:

q/m (charge to mass ratio) = 1.76 * 10^11.

GL, You'll need it.