How to find speed with Faraday's law

In summary, the metal rod can slide on a rail without any friction in the presence of a uniform magnetic field of B=1T which is perpendicular to the plane of the paper. The distance between the tracks is d=0.1m and the resistance given is R=0.1 ohm. The resistance of the rail is negligible and the mass of the rod is m=20g.
  • #1
Jacobs
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Homework Statement


A metal rod can slide on a rail without any friction in the presence of uniform magnetic field of B=1T which is perpendicular to the plane of the paper.The distance between the tracks is d=0.1m and the resistance given is R=0.1 ohm.The resistance of the rail is negligible and the mass of the rod is m=20g. A)How much force must be on the road exerted in order to move it with a constant speed of v=10m/s? B)The rod has been moved for t=2s and then it is released.How much work is dissioated on the resistor till the rop will stop?

Homework Equations


F=IBl=B^2*l^2*v/R

The Attempt at a Solution


According to first formula F=1 but for B i have no idea
 
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  • #2
Welcome to the PF.

Could you please post the figure that goes with this question? It sounds like a classic sliding rail changing the total B*dA, but it's hard for me to be sure from the text of your post. Thanks. :smile:
 
  • #3
1st one
 

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  • #4
You might start here. http://hyperphysics.phy-astr.gsu.edu/hbase/electric/farlaw.html

The rails and the rod and resistor make an electric loop. You can find the area of that loop if you know the length, but for this problem, you are interested in the Change in the area when the rod moves. Since Phi = B*A, phi can change if B changes or (in your case) when A changes. It doesn't do a whole lot of good to have some formulas, unless you have an idea of where they come from. Then you'll understand which ones to use.
 
  • #6
so formula is BdeltaA/delta(t) but still have no idea about how find find change in the area
 
  • #7
Answer of B is 2?
 
  • #8
Jacobs said:
so formula is BdeltaA/delta(t) but still have no idea about how find find change in the area
The motion of the movable rod changes the area.
Jacobs said:
Answer of B is 2?
Please always show your detailed work so we can check it. Thank you.
 
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1. How does Faraday's law relate to speed?

Faraday's law, also known as the law of electromagnetic induction, states that a change in magnetic flux through a conductor will induce an electromotive force (emf) in the conductor. This emf can then produce a current, which can be used to measure the speed of an object.

2. What is the equation for finding speed using Faraday's law?

The equation is v = -dΦ/dt, where v is the speed of the object, dΦ is the change in magnetic flux, and dt is the change in time. This equation is derived from Faraday's law and is known as the motional emf equation.

3. Can Faraday's law be used to find the speed of any object?

Yes, Faraday's law can be used to find the speed of any object as long as it is moving through a magnetic field and a conductor is present to measure the induced emf.

4. How do you measure the change in magnetic flux to use in the speed equation?

To measure the change in magnetic flux, you can use a device called a fluxgate magnetometer or a Hall effect sensor. These devices can measure the strength and direction of a magnetic field, which can then be used to calculate the change in magnetic flux.

5. Are there any limitations to using Faraday's law to find speed?

One limitation is that the object's motion must be perpendicular to the magnetic field for accurate results. Additionally, the conductor used to measure the induced emf must have a constant velocity and be in a closed loop to maintain a constant magnetic flux. Any external interference or variations in the magnetic field can also affect the accuracy of the results.

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