Coulomb's Law and Electrical Fields

In summary, the conversation discusses a problem involving a tiny sphere with a mass of .60g in equilibrium in a horizontal electric field of 700 N/C. The question asks about the magnitude and sign of the charge on the ball, and the conversation goes on to discuss the forces involved and how to find the solution using free body diagrams and equations. Ultimately, the solution is found to be -3.1qC.
  • #1
Yut
7
1

Homework Statement


The tine sphere at the end of the weightless thread has a mass of .60g. It is immersed in air and exposed to a horizontal electric field of strength 700 N/C. The ball is in equlibrium in the position shown. What are the magnitude adn sign of the charge on the ball?

Homework Equations


F=qE
Gravitationa Force= mg
https://fbcdn-sphotos-h-a.akamaihd.net/hphotos-ak-xpf1/v/t34.0-12/10994667_10152670641336806_932307476_n.jpg?oh=9257cdd3e8de5465969a5ec980ec995b&oe=54EDB2B7&__gda__=1424855811_d63d4b9c3de86b44377f76cc1112f998

The Attempt at a Solution


So, since the ball in the equlibrium the forces are balanced.
force downwords due to gravity
mgcosθ
Since the ball moves towords the E field, it should have a negative charge.

So
Fx: F(electrical field)- mgsin =0
qE= mgsinθ
q= mgsinθ / E

I don't get the right answer,
the answer should be -3.1qC
 
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  • #2
F and mg are perpendicular. So mg can't balance the force. Hint: you have forgot to consider another force.
 
  • #3
Is it the force due to the other charge, which will be + and equalt to kq^2 / r^2... and I would find R using sinθSorry, I mized it with other problem.
What other force there could be?
 
  • #4
Its the force exerted by the string. What would have happened if the string was absent? The ball would have moved away. But the string stops and holds the ball inplace. So consider tension force. Draw free body diagram. You should get ##T_y=mg## and ##T_x=F_E##
 
  • #5
Oh, I completely forgot about that, and then it will be Tcosθ, and you find T using the mg=Tsinθ
the euqation there fore will be
F(electrical)- Tsinθ-mgcosθ= 0
and you solve for F(electrical)
F(electrical) = qE

and then you look for q
 
  • #6
Again... I told you F has nothing to do with mg. Its just ##F=Tsin\theta## and ##mg=Tcos\theta##. Find T from 2nd equation and put it on first equation.
 
  • #7
Yes! Here the set up that gave me the right answerhttps://fbcdn-sphotos-h-a.akamaihd.net/hphotos-ak-xpf1/v/t34.0-12/11014718_10152670767961806_1607350090_n.jpg?oh=c796df67fefef907f1ccfe3fbafe9f57&oe=54ECB140&__gda__=1424800785_7febf55bcb55aca57d3a84e1bb4b6827
 
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FAQ: Coulomb's Law and Electrical Fields

What is Coulomb's Law?

Coulomb's Law is a fundamental law in physics that describes the relationship between electrically charged particles. It states that the force of attraction or repulsion between two charged particles is directly proportional to the product of their charges and inversely proportional to the square of the distance between them.

How is Coulomb's Law related to electrical fields?

Coulomb's Law is the basis for understanding electrical fields. The law states that a charged particle creates an electric field around it, which exerts a force on other charged particles. The strength and direction of the electric field is determined by the magnitude and sign of the charges involved.

What is an electric field?

An electric field is a region in space where an electrically charged particle experiences a force. It is a vector quantity, meaning it has both magnitude and direction. The strength of an electric field is measured in newtons per coulomb (N/C) and is represented by the symbol E.

How is the direction of an electric field determined?

The direction of an electric field is determined by the direction of the force that would be exerted on a positively charged particle placed in the field. If the force is repulsive, the direction of the electric field is away from the charged particle, and if the force is attractive, the direction is towards the charged particle.

What are some real-life applications of Coulomb's Law and electrical fields?

Coulomb's Law and electrical fields have numerous applications in our daily lives. Some examples include the functioning of electronic devices such as computers and mobile phones, the operation of electric motors, and the generation and transmission of electricity. They also play a crucial role in medical technologies, such as electrocardiograms and magnetic resonance imaging (MRI).

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