Finding magnitude of torque on a molecule

AI Thread Summary
The discussion revolves around calculating the torque on a carbon monoxide molecule in an electric field. The molecule is a permanent dipole with charges of +3.4E-21 C and -3.4E-21 C, separated by a distance of 0.11 nm. Initially, the user calculated the net force incorrectly, assuming it was non-zero, but later realized the forces cancel each other out. For torque, the correct approach involves using the force on one charge and the distance between the charges, leading to a torque calculation of 5.6E-27 N·m. The conversation emphasizes the importance of understanding the relationship between electric force, charge, and distance in torque calculations.
catan
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Homework Statement



Molecules of carbon monoxide are permanent electric dipoles due to unequal sharing of electrons between the carbon and oxygen atoms. The figure shows the distance and charges. Suppose a carbon monoxide molecule with a horizontal axis is in a vertical electric field of strength 15000 N/C.

The picture they provide is one of 2 circles connected together in a linear line with C on the left and O on the right. The diagram shows them to be .11 nm apart from each other. The C has a +3.4E-21 charge and the O has a -3.4E-21 charge.

A. What is the magnitude of the net force on the molecule?

B. What is the magnitude of the torque on the molecule?


Homework Equations


F = eE
Torque = qEL


The Attempt at a Solution



Ok, so part A I got right. I just used the F = eE equation and got the answer 2.4E-15 and thought that I would be using this for part B.

In part B my book shows the equation qEL = torque. It says that qE is the magnitude of the electric force and L is the length they are from each other.

Torque = (2.4E-15 N) * (1.1E-10 m) = 2.64 E -25

This isn't right though. What am I doing wrong? I really appreciate the help!
 
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catan said:
Ok, so part A I got right. I just used the F = eE equation and got the answer 2.4E-15 and thought that I would be using this for part B.
Is the electric field uniform? I don't understand how you got your answer for the net force on the molecule. (What's the net charge on the molecule?)
 
Oh wait, I just realized the answer to part A is zero because they cancel each other out. I was wrong. So the torque tho I'm supposed to use not the net force but the force on the individual atoms? 3.4E-21

I'm still lost...
 
The maximum torque on a dipole equals the force on one charge times the distance between them. Read about it here: http://hyperphysics.phy-astr.gsu.edu/HBASE/electric/diptor.html"
 
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to find the force on each molecule, you divided by the radius squared. don't do that - multiply by the distance instead--traditonally torque is distance * force

so it is 15000 * 3.4*10^-21 * .11*10^-9 = 5.6*10^-27
 
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