# Homework Help: Question with large number?electron charge?

1. Jul 31, 2009

### graphicer89

Question with large number???electron charge?

1. The problem statement, all variables and given/known data

The electric charge of an electron is -1.6 x 10^-19 C. What is the force exerted between two electrons separated by one meter? Is it attractive or repulsive?

2. Relevant equations

F= K Q1Q2 / D^2

3. The attempt at a solution

Im horrible with large numbers and especially at negative exponents....so this is a guess

K = 9x 10^9 N x m^2/c^2

Q1 = -1.6 x 10^-19 C
Q2 = -1.6 x 10^-19 C
D= 1 m

F= 9 x 10 ^9 N x m^2 X ( -1.6x 10 ^-19 C x -1.6x 10 ^-19 C / 1^2 m)

F= 9 x 10 ^9 N x m X (3.2 x 10^19 C^2 )
F= 28.8 x 10^28 NxmxC^2.....is the answer i got....

I know i am completely off but how can i do this ...this is basically math but im just not with well large numbers...

2. Jul 31, 2009

### rl.bhat

Re: Question with large number???electron charge?

F= 9 x 10 ^9 N x m X (3.2 x 10^19 C^2 )
This step is wrong. -1.6x10^-19 X -1.6x10^-19 = ?

3. Jul 31, 2009

### graphicer89

Re: Question with large number???electron charge?

Thats the thing i dont know...do you add the exponents together??

2.56 x 10^-38????

1.6 x 1.6 = 2.56 but what about the 10^-19? do i add them or does it stay the same????

Actually now i got 2.6 x 10 ^-38...by multiplying both

Last edited: Jul 31, 2009
4. Aug 1, 2009

### rl.bhat

Re: Question with large number???electron charge?

This is correct.

5. Aug 1, 2009

### Redbelly98

Staff Emeritus
Re: Question with large number???electron charge?

Yes, you add the exponents when you are multiplying two numbers.

Do you have a calculator that you can double-check things like this? If not, Google can be used as a calculator:

Note the computer-standard "e-19" to signify "×10-19 "

6. Aug 1, 2009

### graphicer89

Re: Question with large number???electron charge?

Ok so after i have 2.6 x 10^-38 is it C^2?

7. Aug 1, 2009

### graphicer89

Re: Question with large number???electron charge?

Well let me put what i have..... F=9 x 10^9 N x m^2/c^2 X( 2.6 x 10^-38 c^2 /1 m^2)

that is what i have...do i cancel out the m^2 and c^2? from both sides? so that only the N is remaining?

8. Aug 1, 2009

### rl.bhat

Re: Question with large number???electron charge?

Yes. Force should be in N.

9. Aug 1, 2009

### graphicer89

Re: Question with large number???electron charge?

Cool so if i did my calculations right....i got 2.3 x 10^-28 N am i close or am i really off? but i think this force is repulsive no??? because its a positive number .......or is it attractive?

10. Aug 1, 2009

### rl.bhat

Re: Question with large number???electron charge?

Like charges repel each other.

11. Aug 1, 2009

### Redbelly98

Staff Emeritus
Re: Question with large number???electron charge?

Exactly. The equation gives the magnitude of the force. Use the opposites attract / likes repel rule to figure out the direction.