Physics 30 - Static Electricity

[Kylah]

[SOLVED] Physics 30 - Static Electricity

Imagine that you have an object with an unknown electrostatic charge. If you are given a rubber rod, fur, and a neutral electroscope, describe how you could find the type of charge on the object.
My answer: By rubbing the rod on the fur, the fur will deposit some of its electrons onto the rod. The rod would then be negatively charged. If the object is attracted to the negatively charged rod, we can infer it is positive. If the object is repelled, it can be assumed the object is also negatively charged. So what I'm wondering is, where does the neutral electroscope come into hand? Did I do this question entirely wrong? Miss a step? Or did they just throw that into mess me up?


2. Two objects are separated by a distance of 2.00 m where q1= -3.00 C and q2 = 4.00 C.
A) Calculate the magnitude of the electrostatic force between the two charges.
I used F=((Kq1q2)/r2) and got an answer of -2.70 x 10^10. Is that the right way to do this question/does that seem like the right answer? And how do I know if it's attracting or repelling?

B)Imagine that the two identical objects are brought to the middle, touched to each other, and then returned to their original positions. Determine the new charge on each object. Concisely explain your answer. Use your answer to calculate the new electrostatic force between the objects.
I'm going to be honest here, I'm totally lost...


3. A charge of -4.27 x 10^-8 C experiences an electrostatic force of repulsion of 7.91 x 10^-4 N, north.
A) Calculate the magnitude of the electric field at the point in space occupied by the charge.
I used E=F/q and got -1.85 x 10^4 N/C. Does that seem right?
B) Determine the direction of the electric field. Explain your answer.
Again, I don't know how to figure this out.

A lightning bolt can deliver up to 20 C of charge to Earth.
A) Calculate the number of electrons transferred from the cloud to the ground in this discharge.
I went 20.0 C/1.60 x 10^-19 C and got 1.25 x 10 ^20 electrons. I'm not sure if that's the correct procedure though.
B)Explain why a bolt of lightning looks jagged.
I wrote: A bolt of lightning will take a jagged path because the negative charges are attracted to the pockets of positive charge which are randomly dispursed throughout the atmosphere.


Thanks in advance for any help. It's greatly appreciated.

 

[kamerling]

1. the object and the rod are likely too heavy and the charge too small to directly measure the attraction.

2a The value of F is OK. you know opposite charges attract?
2b if object 1 has 3 coulombs of electrons extra and object 2 lacks 4 coulomb of electrons, what will happen if you bring them together? (I assume the objects are conducting)

3a for the magnitude, you want a positive number.
3b the direction is the magnetic field is the direction of the force on a positive charge

4a Ok

 

[Moetasim]

Hi there! It looks like you have a good understanding of the concepts involved in these questions. Let me help clarify a few things for you.

First, regarding the use of the neutral electroscope in the first question, you are correct in using it to determine the type of charge on the object. By bringing the object close to the electroscope, you can observe if there is a deflection in the indicator. If the object is positively charged, the electroscope will be attracted to it and the indicator will move towards it. If the object is negatively charged, the electroscope will be repelled and the indicator will move away from it.

For question 2, your calculations for the electrostatic force are correct. The negative sign indicates that the force is attractive, meaning the two objects will be pulled towards each other. When they are touched and then separated, the charges will redistribute evenly, resulting in a new charge of 0 on each object. The new electrostatic force will be 0 as well.

For question 3, your calculations for the magnitude of the electric field are correct. The negative sign indicates that the electric field is directed towards the south (opposite direction of the force). This is because the charge experiencing the force is negative, so the electric field will be directed away from it.

For the last question, your calculations for the number of electrons transferred are correct. And your explanation for why lightning looks jagged is also correct. The charges are attracted to each other, but the path of least resistance is not always a straight line, resulting in a jagged path.

I hope this helps clarify things for you. Keep up the good work in your studies of physics and static electricity!