Electromagnetism Exercise

[wingnut]

Re Ex 2....

The first problem you ignore the charges movement
Use F = k x Q1 x Q2/r^2 to work out force between Q1 and Q2 where r =.1m

This force is counterbalanced by F = k Q1 x Q3/.3^2

If you understand the principle of inverse squared, if you triple the distance apart of the charge (Q3 vs Q2) you get 1/9 the force.

Thus logic tells me that Q3 must be = 9 x Q2

But you prove that for yourself using the formulae above, and figure out what its charge must be and give me your answers for the forces.

 

[PostMortem]

Re Ex 2....

The first problem you ignore the charges movement
Use F = k x Q1 x Q2/r^2 to work out force between Q1 and Q2 where r =.1m

This force is counterbalanced by F = k Q1 x Q3/.3^2

If you understand the principle of inverse squared, if you triple the distance apart of the charge (Q3 vs Q2) you get 1/9 the force.

Thus logic tells me that Q3 must be = 9 x Q2

But you prove that for yourself using the formulae above, and figure out what its charge must be and give me your answers for the forces.

I found Q3 to be -18nC using this formula: Q3/X1^2+Q2/x2^2=0
Thank you I think I understand everything a little better now.
Also using the formula you mentioned above in the first exercise i found Q to be 8,8*10^-6 nC ..Not sure if its right.
Thank you again for all your help!