Finding magnitude of torque on a molecule

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Homework Help Overview

The discussion revolves around calculating the torque on a carbon monoxide molecule in an electric field. The molecule is described as a permanent electric dipole, with specific charges and distances provided. Participants are exploring the implications of these characteristics in relation to the torque and net force acting on the molecule.

Discussion Character

  • Mixed

Approaches and Questions Raised

  • Participants discuss the application of the torque equation and question the assumptions regarding the net force on the molecule. There is confusion about whether to use the net force or the force on individual charges for calculating torque.

Discussion Status

Some participants have identified errors in their initial calculations and are reconsidering their approach. There is an ongoing exploration of the correct application of formulas related to torque and electric forces, with references to external resources for clarification.

Contextual Notes

Participants are navigating the complexities of electric dipoles and the effects of an electric field, including the uniformity of the field and the resultant forces on the individual charges. There is a noted lack of consensus on the correct method for calculating torque, with various interpretations being discussed.

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"
 
Last edited by a moderator:
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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