Magnetostatics - Rotation of circular disc

In summary, the problem involves a rotating disc with a given radius and angular frequency, and a magnetic flux density. A load is suddenly connected and the question asks how long it will take for the disc to slow to half its initial speed. The solution involves using equations for emf and kinetic energy. The correct answer is T = 6.16s.
  • #1
Keano16
23
0

Homework Statement




A disc has radius a and rotates with angular frequency w. Magnetic flux density is B. Such a disc of mass 10^4 kg and radius 3m is rotating freely at 3000 revs/min in a field of 0.5T. A load of 10^-3 ohms is connected suddenly between the rim and the axis of the disc. How long would it take the disc to slow to half its initial speed?


Homework Equations





The Attempt at a Solution



I found an equation for the emf produced that is: w*a^2*B/2 . Using this I wanted to equate two equations -- kinetic energy of the rotating disc at half the intiial speed = (V^2/R)*T.

The answer is meant to be T=6.16s, but that's not what I have.

Thanks for any help.
 
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  • #2
Keano16 said:
I found an equation for the emf produced that is: w*a^2*B/2 . Using this I wanted to equate two equations -- kinetic energy of the rotating disc at half the intiial speed = (V^2/R)*T.

No, the loss in kinetic energy should be equal to (V^2/R)*T.
 
  • #3
Ah I see now -- thanks for your help!
 

1. What is magnetostatics?

Magnetostatics is a branch of electromagnetism that deals with the study of the static magnetic fields produced by electric currents. It is concerned with the behavior of magnetism in the absence of time-varying electric fields.

2. What is the rotation of a circular disc in magnetostatics?

The rotation of a circular disc in magnetostatics refers to the behavior of a disc-shaped object when placed in a static magnetic field. The disc may rotate due to the interaction between the magnetic field and the electric current flowing through the disc.

3. What factors affect the rotation of a circular disc in magnetostatics?

The rotation of a circular disc in magnetostatics can be affected by several factors, including the strength and direction of the magnetic field, the amount of current flowing through the disc, and the shape and size of the disc.

4. How is the rotation of a circular disc in magnetostatics calculated?

The rotation of a circular disc in magnetostatics can be calculated using the principles of torque and angular momentum. The magnitude and direction of the torque acting on the disc can be determined by considering the magnetic field, current, and geometry of the system.

5. What are some real-world applications of the rotation of circular discs in magnetostatics?

The rotation of circular discs in magnetostatics has various practical applications, such as in electric motors, generators, and magnetic levitation systems. It is also used in devices such as MRI machines and particle accelerators.

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