Sphere Charge Hanging on Thread (Electric Field Question)

In summary: This is a good problem to show that!In summary, the conversation was about a physics problem involving two charges, one hanging from a thread and the other brought close to it. The tension in the thread and the charge on the second charge was to be calculated. Through a series of calculations, it was determined that the tension in the thread was 1.92 N and the charge on the second charge was +/- 4.7x10-6 C, with the positive choice being the correct solution due to the fact that the two charges had the same magnitude and opposite signs. The expert gave positive feedback on the solution and encouraged the person to trust their physics knowledge.
  • #1
HarleyM
56
0

Homework Statement


Charge 1 (0.15 kg) in the following diagram is hanging from a light insulating thread, as shown in diagram (red is what I have added myself)
diagram2.png

Charge 2 is brought close and pulls charge 1 , deflecting the string away from the vertical axis by 40 degrees. The charges have the same magnitude, charge 1 is negative.

A) Find the tension in the thread
B) Find the charge on 2.

Homework Equations


Fg=mg
Fe=Kq2/r2


The Attempt at a Solution



Vertical

Fnet=0
0=FtCos40 + (-mg)
Ft=mg/cos40
Ft=1.92

Horizontal

Fnet=0
0=Fe+(-Ftsin40)
0=kq2/r2+(-1.92sin40)
q=√(1.92sin40)(0.42)/(9x109)
q=+/- 4.7x10-6C

How does this look?

diagram3.png
 
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  • #2
Is there anything about that which concerns you?
How could you work out for yourself if you got the right answer?

FWIW: without crunching the numbers, your reasoning looks sound.
Comment the actual paper you hand in.
 
  • #3
the answer q=+/- 4.7x10-6 C is not correct. Read the problem again. It says
The charges have the same magnitude, charge 1 is negative.

Do the charges attract or repel? What is charge 2 then?

ehild
 
  • #4
Well I wrote +/- because it was a square root, the charge is actually positive I know because it attracts charge 1

Thank you for the input however I feel more confident with my physics knowledge everyday !
 
  • #5
HarleyM said:
Well I wrote +/- because it was a square root, the charge is actually positive I know because it attracts charge 1

Then it was correct but it was not the solution yet.

HarleyM said:
Thank you for the input however I feel more confident with my physics knowledge everyday !

It was a nice solution. I especially liked the picture. You can be confident in your knowledge! :smile:

ehild
 
  • #6
It is common for the math to give a choice of solutions - you pick the one that makes sense in terms of the physics.
 

1. What is the electric field around a sphere charge hanging on a thread?

The electric field around a sphere charge hanging on a thread depends on the charge of the sphere, the length of the thread, and the material of the thread. It can be calculated using the formula: E = kQ/r^2, where k is the Coulomb's constant, Q is the charge of the sphere, and r is the distance from the center of the sphere to the point where the electric field is being measured.

2. How does the electric field change as the length of the thread is increased?

The electric field decreases as the length of the thread is increased. This is because the electric field is inversely proportional to the square of the distance from the center of the sphere, and as the length of the thread increases, the distance from the center of the sphere also increases.

3. What happens to the electric field if the charge on the sphere is doubled?

If the charge on the sphere is doubled, the electric field will also double. This is because the electric field is directly proportional to the charge of the sphere. Therefore, increasing the charge will result in a stronger electric field.

4. Can the material of the thread affect the electric field around the sphere charge?

Yes, the material of the thread can affect the electric field around the sphere charge. This is because different materials have different dielectric constants, which can alter the electric field. Materials with a higher dielectric constant will result in a stronger electric field, while materials with a lower dielectric constant will result in a weaker electric field.

5. Is the electric field around the sphere charge uniform?

The electric field around a sphere charge hanging on a thread is not uniformly distributed. It is strongest near the surface of the sphere and decreases as the distance from the sphere increases. This is due to the nature of electric field lines, which originate from the surface of the sphere and spread out in all directions.

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