What is the net charge after adding electrons?

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Homework Help Overview

The problem involves calculating the net charge of a metal sphere initially charged at +7.0 µC after adding a specific number of electrons. The context is centered around electrostatics and charge calculations.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the charge of an electron and its multiplication by the number of electrons added. There are questions about significant figures and the correct interpretation of the initial charge. Some participants express confusion regarding calculator outputs and rounding errors.

Discussion Status

There is an ongoing exploration of the calculations involved, with some participants providing insights into potential errors and clarifications regarding significant figures. The discussion reflects a mix of interpretations and attempts to clarify the mathematical process without reaching a definitive conclusion.

Contextual Notes

Participants are navigating issues related to significant figures in the context of charge calculations, and there is mention of a possible misunderstanding regarding calculator outputs. The original poster expresses uncertainty about the correctness of their calculations.

rcmango
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Homework Statement



A metal sphere has a charge of +7.0 µC. What is the net charge after 8.00 10^13 electrons have been placed on it?
in µC


Homework Equations





The Attempt at a Solution



I believe that the charge of an electron is: -1.6 x 10^-19 C
and there are 8 electrons,

so -1.6 x 10^19 C * 8.00 x 10 ^13 electrons right?

then I add it to 7 uC? well I'm having trouble with the sigfigs, I got 5.72 uC I don't believe that is correct.

please help.
 
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Do you have a rounding error? I am getting -5.8µC.
 
ah, I see from your answer. Sometimes it just takes someone else.

it was my sign! it has to be negative.

Thankyou!
 
also, when i get the answer, after multiplying the electrons, does +7.0 uC have sigfigs? i can't seem to figure out why my calculator won't give me anything past 1.28 x 10^33 i believe.
 
rcmango said:
also, when i get the answer, after multiplying the electrons, does +7.0 uC have sigfigs? i can't seem to figure out why my calculator won't give me anything past 1.28 x 10^33 i believe.

Sorry I don't understand your calculator comment. 7.0µC has 2 significant figures, and it means [itex]7.0*10^{-6}[/itex]C. 7.00µC would be 3 sig figs, and 7µC would be 1 sig fig.
 

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