Rotating Coil in Magnetic Field

Click For Summary

Homework Help Overview

The discussion revolves around calculating the magnetic field (B) using a search coil, based on the charge passing through the coil during its rotation in a magnetic field. The problem involves understanding the relationship between charge, current, resistance, and electromagnetic induction as described by Faraday's law.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants explore the relationship between charge, current, and resistance, questioning how to incorporate these into the calculation of magnetic flux change. There are attempts to derive equations linking these concepts, with some participants expressing uncertainty about the role of the coil's area and the number of turns in the calculations.

Discussion Status

The discussion is active, with participants providing insights into the relationships between the variables involved. Some guidance has been offered regarding the need to consider time in Faraday's law, and there is an ongoing exploration of how to correctly apply the equations to arrive at a solution.

Contextual Notes

Participants are navigating the constraints of the problem, including the fixed area of the coil and the need to account for the number of turns in their calculations. There is a recognition of the complexity involved in integrating these concepts correctly.

dukesolice
Messages
4
Reaction score
0

Homework Statement


[/B]
Magnetic field values are often determined by using a device known as a search coil. This technique depends on the measurement of the total charge passing through a coil in a time interval during which the magnetic flux linking the windings changes either because of the motion of the coil or because of a change in the value of B. As a specific example, calculate B when a 61-turn coil of resistance 194Ω and cross-sectional area 44.5m^2 produces the following results: A total charge of 4.76E-4C passes through the coil when it is rotated in a uniform field from a position where the plane of the coil is perpendicular to the field to a position where the coil's plane is parallel to the field.

Homework Equations


emf = -change in flux

The Attempt at a Solution



emf = -d/dt (integral of B dot dA)

The change in flux is from when the coil is perpendicular to the field to when the coil is parallel to the field. So 90 degrees. But I don't know how to get the change the in area, and how to use the charge and resistance.
 
Physics news on Phys.org
dukesolice said:
But I don't know how to get the change the in area, and how to use the charge and resistance.
The shape of the coil doesn't change as the coil rotates. So, the area of the coil remains constant.

You'll need to bring together several elementary concepts in this problem. How is charge related to current and time? How is current related to resistance and emf?
 
TSny said:
The shape of the coil doesn't change as the coil rotates. So, the area of the coil remains constant.

You'll need to bring together several elementary concepts in this problem. How is charge related to current and time? How is current related to resistance and emf?

Current is charge/time. Emf = current * resistance.
 
dukesolice said:
Current is charge/time. Emf = current * resistance.
OK. These relations along with Faraday's law give you everything you need.

Try combining them to get a relation between the total charge and the change of flux.
 
dukesolice said:

Homework Equations


emf = -change in flux
This is not correct. Faraday's law also involves time.
 
So now I have dQ/dt * R = -d(flux)/dt, so then I took integral of both sides and got NRQ = -BA, where N is number of coils, this gave me the wrong answer
 
dukesolice said:
So now I have dQ/dt * R = -d(flux)/dt,
OK, but should the number of turns, N, appear somewhere here?

so then I took integral of both sides and got NRQ = -BA, where N is number of coils, this gave me the wrong answer
Show the steps in getting to this result. Why does N appear on the left?
 

Similar threads

Trace on the screen of a C.R.O. when a deflection coil is rotated
  • · Replies 9 ·
Replies
9
Views
1K
EMF induced by a magnet falling through a coil
  • · Replies 4 ·
Replies
4
Views
3K
Eddy currents in Faraday's Law Experiment
  • · Replies 3 ·
Replies
3
Views
2K
Torque on a rectangular coil in a uniform magnetic field
  • · Replies 7 ·
Replies
7
Views
4K
AC generator -- Understanding coil voltages as function of position
  • · Replies 1 ·
Replies
1
Views
2K
Origin of repulsive force on a magnet approaching conducting ring?
  • · Replies 5 ·
Replies
5
Views
2K
EMF shielding using a conductor
  • · Replies 6 ·
Replies
6
Views
2K
Forces acting on a coil due to a varying magnetic field
  • · Replies 12 ·
Replies
12
Views
3K
Will EMF be induced in a coil that is accelerating in a uniform magnetic field?
  • · Replies 4 ·
Replies
4
Views
1K
Calculating Magnetic Field Strength and Force of Eddy Currents in a Solenoid
  • · Replies 49 ·
2
Replies
49
Views
6K