Thread: calculate the net charge.

A metal sphere has a charge of +7.0 µC. What is the net charge after 8.00 1013 electrons have been placed on it?
in µC

anyone able to help me with this one please.

Originally Posted by rcmango

A metal sphere has a charge of +7.0 µC. What is the net charge after 8.00 1013 electrons have been placed on it?
in µC

anyone able to help me with this one please.

You mean 8.00 x 10^13 electrons?

Well the charge of a single electron is -1.6 x 10^-19 C. So 8 x 10^13 electrons has a charge of...

-Dan

Originally Posted by rcmango

A metal sphere has a charge of +7.0 µC. What is the net charge after 8.00 1013 electrons have been placed on it?
in µC

anyone able to help me with this one please.

Well here's a start: How many coulomb is 8.00 1013 electrons? (You might need to refer to your class notes for the conversion). This NEGATIVE charge is added to +7.0 µC.

Originally Posted by topsquark

You mean 8.00 x 10^13 electrons?

Well the charge of a single electron is -1.6 x 10^-19 C. So 8 x 10^13 electrons has a charge of...

-Dan

So couldn't be just -1.6 x 1^-19 C * 8 x 10^13?

then add that to 7uC?

i'm getting confused from sig figs i think.

Originally Posted by rcmango

So couldn't be just -1.6 x 1^-19 C * 8 x 10^13? Mr F says: Yes.

then add that to 7uC? Mr F says: Yes.

i'm getting confused from sig figs i think. Mr F says: You wouldn't be the first.

..

thanks got it, -5.72 uC

Except I have
A metal sphere has a charge of +8.0 µC. What is the net charge after 8.00 x 10^13 electrons have been placed on it

Everytime I try doing

(-1.6x10^-19) x (8.00x10^13) + 8 = 7.9999872

But thats not the correct answer.

Why is that not working???