Charged particles deflecting in a statics question.

davidmn
Messages
2
Reaction score
0
[SOLVED] Charged particles deflecting in a statics question.

Homework Statement



A particle mass 2g and carrying a charge of q is suspended from a light, insulating thread. A second particle carrying an equal and opposite charge is held near to the first particle in the same horizontal plane and causes it to deflect. When the particles are separated by 25cm it is observed that the thread makes an angle of 45° to the vertical. By considering the forces acting on the suspended particle, find the magnitude of q.

Homework Equations


F=Qq/(4∏ε r^2)
Trigonometry
Statics


The Attempt at a Solution


I've assumed that the 25cm is measured between the particles before the deflection.
I've drawn a force diagram and resolved the forces relative to the force from the stationary particle. So 2gsin(45) is acting downwards, tension in in the string acts in opposition to the electrostatic force and 2gcos(45). I am at a loss as to what is acting in opposite to the 2gsin(45). I can take a photo of what I have if anyone isn't clear on what I've done.
 
Last edited:
Physics news on Phys.org
Your assumption does not correspond to the wording of the question.

Quote: "When the particles are separated by 25cm it is observed that the thread makes an angle of 45° to the vertical".
 
Ah. True. OK I have two answers now. They make sense, one for if g=9.81 and another for if g=the unit. Thank you very much.
 
Thread 'Need help understanding this figure on energy levels'
This figure is from "Introduction to Quantum Mechanics" by Griffiths (3rd edition). It is available to download. It is from page 142. I am hoping the usual people on this site will give me a hand understanding what is going on in the figure. After the equation (4.50) it says "It is customary to introduce the principal quantum number, ##n##, which simply orders the allowed energies, starting with 1 for the ground state. (see the figure)" I still don't understand the figure :( Here is...
Thread 'Understanding how to "tack on" the time wiggle factor'
The last problem I posted on QM made it into advanced homework help, that is why I am putting it here. I am sorry for any hassle imposed on the moderators by myself. Part (a) is quite easy. We get $$\sigma_1 = 2\lambda, \mathbf{v}_1 = \begin{pmatrix} 0 \\ 0 \\ 1 \end{pmatrix} \sigma_2 = \lambda, \mathbf{v}_2 = \begin{pmatrix} 1/\sqrt{2} \\ 1/\sqrt{2} \\ 0 \end{pmatrix} \sigma_3 = -\lambda, \mathbf{v}_3 = \begin{pmatrix} 1/\sqrt{2} \\ -1/\sqrt{2} \\ 0 \end{pmatrix} $$ There are two ways...
Back
Top