Intro to Electromagnetism: five conceptual questions

In summary: When the wire is cut, the negative charges would remain stuck in sphere #1, giving it a negative charge.In summary, for each of the five questions, there are four possible responses: Positive, Negative, Neutral, or Cannot Tell. A positively charged ball near a neutral isolated conductor will induce a negative charge in the conductor when grounded and removed. A positively charged glass rod will attract a neutral or negative object suspended by a non-conducting thread. A negatively charged glass rod will only repel a neutral object suspended by a non-conducting thread. A positive point charge near a neutral conducting sphere will move in the negative x direction. And the charge on sphere #1 after a positively charged glass rod is brought near and then removed is
  • #1
EMJ
2
0
Hello! I'm working on an online assignment and am on my last chance to submit the right answer, so I figured I'd ask here for some help to see where my reasoning is wrong.

Problem:
For each of the five questions, I can choose one of four responses: Positive, Negative, Neutral, or Cannot Tell.

A. A positively charged ball is brought close to a neutral isolated conductor. The conductor is then grounded, while the ball is kept close. If the ground connection is first removed and then the ball is taken away, the conductor has a _______ charge.

B. A positively charged glass rod attracts an object suspended by a non-conducting thread. The charge on the object is _______ .

C. A negatively charged glass rod repels an object suspended by a non-conducting thread. The charge on the object is _______ .

D. A positive point charge is brought near the outside surface of a neutral conducting sphere and released. The initial position of the point charge is on the on the positive x-axis and the sphere is centered on the origin. The point charge moves in the _______ x direction. (If the point charge does not move, select "Cannot tell".)

E. Two neutral metal spheres, #1 and #2, are mounted on insulating supports. They are connected by a wire. A positively charged glass rod is brought near sphere #1. The wire connecting the spheres is removed and the charged rod is then taken away. Now the charge on sphere #1 is _______ .

My Latest Answers and Reasoning:

A. Negative
Neutral objects can still have induced charge. So, when the positive ball is introduced, the negative charge is attracted to it. When it is connected to the ground, electrons are donated from the ground into the initially neutral object, making it net negative. When the connection the ground in removed, the negative charge is stuck in the conducting object, making it negatively charged.

B. Cannot Tell
Attractions can be produced between oppositely charged objects, but also can be induced between a charged and neutral object. If the suspended object is negative, it would be attracted to the positively charged rod. If the suspended object is neutral, the charges can rearranges so that the electrons are pooled towards the direction of the rod, producing an attraction. Therefore, we cannot tell whether the suspended object is negative or neutral.

C. Positive
Unlike attractions, repulsions can only be caused between two of the same charges. This is because is an object is charged (say, positively) and another object is neutral, when the positively charged object approaches the neutral object, the negative charges in the neutral objects will pool towards the positive object. The negative charges in the neutral object will always be closer in distance to the positive object, than the neutral object's positive charges. Therefore induced charge can only produce an attraction.

D. Negative
I'm less sure about this one.
I feel like the neutral object's charges will rearrange so that its negative charges pool towards the positive point charge? However the fact that it's a point charge and not a charged object gets to me. Perhaps it's too insignificant compared to the charged object to cause an attraction or repulsion?

E. Can't Tell
Even less sure about this one.
I initially thought that sphere #1 would be negatively charged, because the positively charged rod would make the negative charge from sphere #1 and #2 pool in sphere #1 towards the rod (and the negative charges from sphere #2 would go to sphere #1 through the wire). When the wire is cut, the negative charges would remain stuck in sphere #1, giving it a negative charge.
When I was reviewing all my false submissions and didn't know what to change, I figured maybe it was a trick question because they don't specify the wire is conducting and is instead insulating? In which case, sphere #1 would have remained neutral... So the sphere could be negative or neutral.

My Previously Submitted (False) Attempts:
1.
A. Negative
B. Cannot Tell
C. Positive
D. Cannot Tell
E. Negative

2.
A. Negative
B. Cannot Tell
C. Positive
D. Negative
E. Negative

3.
A. Negative
B. Negative
C. Positive
D. Cannot Tell
E. Negative

4.
A. Negative
B. Negative
C. Positive
D. Negative
E. Negative

5.
A. Negative
B. Cannot Tell
C. Positive
D. Negative
E. Cannot Tell

I'd appreciate any help :smile: Thanks!
 
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  • #2
I get the same answers as you except on E. The word "wire" normally implies that it is conducting.
 
  • #3
You seem to think that
EMJ said:
If the suspended object is neutral, the charges can rearranges so that the electrons are pooled towards the direction of the rod, producing an attraction.
Is that always the case? I think not; it only happens with conductors in which charges are free to move about. It does not happen with insulators. So consider that anything referred to as an "object" could be either a conductor or an insulator. I agree with @berkeman about E but I disagree about C. Your reasoning in C is correct, but your most recent answer for C is inconsistent with that reasoning.
 
  • #4
kuruman said:
I disagree about C. Your reasoning in C is correct, but your most recent answer for C is inconsistent with that reasoning.
Oops, I'm dyslexic apparently. Thanks for catching that @kuruman
 

Related to Intro to Electromagnetism: five conceptual questions

1. What is electromagnetism?

Electromagnetism is the branch of physics that deals with the relationship between electricity and magnetism. It describes how electrically charged particles interact with each other and with magnetic fields.

2. What is the difference between electricity and magnetism?

Electricity refers to the movement of electrically charged particles, while magnetism refers to the force exerted by magnets on certain materials. However, they are closely related and can be thought of as different aspects of the same phenomenon.

3. What is an electromagnetic field?

An electromagnetic field is a physical field that is created by electrically charged particles and is responsible for the interactions between electrically charged particles and magnetic fields.

4. How does an electric current create a magnetic field?

An electric current consists of moving electrically charged particles. When these particles move, they create a magnetic field around them, which can be visualized as a series of concentric circles around the current.

5. What are some real-life applications of electromagnetism?

Electromagnetism has a wide range of applications in everyday life, including generators and motors, electric circuits, and communication technologies such as radio, television, and cell phones. It is also used in medical imaging techniques such as MRI and in the production of electricity through hydroelectric dams and wind turbines.

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