Question with large number?electron charge?

[graphicer89]

Question with large number?electron charge?

Homework Statement

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?

Homework Equations

F= K Q1Q2 / D^2

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 I am just not with well large numbers...

 

[rl.bhat]

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 = ?

 

[graphicer89]

F= 9 x 10 ^9 N x m X (2.56 x 10^19 C^2 )
This step is wrong. -1.6x10^-19 X -1.6x10^-19 = ?

Thats the thing i don't 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

 

[rl.bhat]

Thats the thing i don't know...do you add the exponents together??

2.56 x 10^-38?


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

This is correct.

 

[Redbelly98]

Thats the thing i don't know...do you add the exponents together??

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:

http://www.google.com/#hl=en&q=1.6e...aq=f&oq=1.6e-19+*+1.6e-19&aqi=&fp=MyO-rnw0Pu0

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

 

[graphicer89]

This is correct.

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

 

[graphicer89]

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?

 

[rl.bhat]

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?

Yes. Force should be in N.

 

[graphicer89]

Yes. Force should be in N.

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?

 

[rl.bhat]

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?

Like charges repel each other.

 

[Redbelly98]

Like charges repel each other.

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