A solenoid and a wire

In summary, a solenoid with a radius of 0.05m, 800 loops per meter, and a resistance of 0.2Ω is not connected to an ideal voltage source. Two loops of wire are bound around the solenoid and attached to a resistor with a resistance of 0.8Ω. When the voltage source is connected, the direction of the current in the wire is from A to B. The total amount of charge that flows through the resistor can be calculated by integrating Faraday's law of induction, which can be simplified to ΔQ = N*Δ∅/R. However, when calculating the change in flux, it is not necessary to multiply by N again as it
  • #1
Eitan Levy
259
11

Homework Statement


[/B]
A solenoid is not connected to an ideal voltage source.
Its radius is 0.05m, it has 800 loops per meter and its resistance is 0.2Ω. ε=120V.
Around the solenoid we bind two loops of a wire. The loops are attached to a resistor with the resistance of 0.8Ω.
Suddenly, we connect the voltage source.
What is the direction of the current in the wire?
What is the total amount of charge that flows through the resistor?

Homework Equations


B=μ0nI.
ε=IR

The Attempt at a Solution


I succesfully calculated that the change in the flux would be -9.47*10-3Wb.
Regarding the first question, I thought that inside the solenoid a magnetic field is created pointing to the right (but I am really not sure about it). So the wire will have to create a magnetic flux pointing to the left, and that in order to do so the current will have to flow from A to B.
Regarding the second question, I simply don't understand how can we know when current will not flow anymore in the wire? When does it stop and why?
 

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  • #2
Eitan Levy said:
Regarding the first question, I thought that inside the solenoid a magnetic field is created pointing to the right (but I am really not sure about it).
Yes. If you want to check your understanding of this, please explain how you deduced the direction of the field of the solenoid.

So the wire will have to create a magnetic flux pointing to the left, and that in order to do so the current will have to flow from A to B.
Yes.
Regarding the second question, I simply don't understand how can we know when current will not flow anymore in the wire? When does it stop and why?
It is interesting that you don't need to know the details of how the current changes with time. Hint: Integrate Faraday's law of induction.
 
  • #3
TSny said:
Yes. If you want to check your understanding of this, please explain how you deduced the direction of the field of the solenoid.

Yes.
It is interesting that you don't need to know the details of how the current changes with time. Hint: Integrate Faraday's law of induction.

I reached this conclusion by rotating the solenoid by 90 degrees and then using the second right hand rule, definitely not the most simple way.
Okay, so I had this idea:
ε=N*Δ∅/Δt
ΔQ/Δt*R=N*Δ∅/Δt
ΔQ=N*Δ∅/R.
I thought that because we have 2 loops I need to multiply by N (by 2). However according to the book it's wrong (The correct answer is when you don't multiply by N), why?
Perhaps it's because I already multiplied by 2 when I calculated the flux?
 
  • #4
Did you already multiply by 2 in finding the value of the change in flux that you stated in your first post?
 
  • #5
TSny said:
Did you already multiply by 2 in finding the value of the change in flux that you stated in your first post?
Yes, I figured that was the problem.
 

1. What is a solenoid?

A solenoid is a coil of wire that is used to create a magnetic field when an electric current is passed through it.

2. How does a solenoid work?

When an electric current flows through the wire in a solenoid, it creates a magnetic field that is strongest inside the coil. This magnetic field can be used to move objects, such as metal cores, within the solenoid.

3. What is the difference between a solenoid and a wire?

A wire is a simple conductor of electricity, while a solenoid is a specific type of wire that is designed to create a magnetic field when an electric current is passed through it.

4. What are some applications of a solenoid?

Solenoids have many practical applications, such as in electric motors, door locks, and valves. They are also used in scientific experiments and equipment, such as particle accelerators and magnetic resonance imaging (MRI) machines.

5. How can a solenoid be controlled?

A solenoid can be controlled by varying the amount of electric current passing through the wire, or by changing the direction of the current. This can be done manually or through electronic circuits and devices.

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