1
$\begingroup$

So the device is a Galvanometer.
According to the Lenz's Law, when we take the magnet towards the coil, the pole at the right end, should be north pole and when we take it away, the pole should be south. And the reason is inertia.
And my question(s) are-
1. If we take the magnet inside, due to inertia, the pole formed is north. Okay. Now, by:

the direction of current in the first figure observed from the right side, should be, anti-clockwise. But this is the direction of conventional current, which is not true in real. In real, electrons move, so due to inertia, the direction of the current should be reverse. (From the point of view of Lenz's Law).
2. A Galvanometer shows the direction of a conventional current, so isn't the device in figure one showing the wrong/reverse deflections?

|cite|improve this question
$\endgroup$
  • $\begingroup$ Explain the downvote, downvoter. $\endgroup$ – Aditya Agarwal Sep 3 '15 at 10:33
  • $\begingroup$ how are you relating electron movement to inertia ? $\endgroup$ – Shubham Sep 16 '15 at 16:23
  • $\begingroup$ This is what is the basic principle of Lenz law. $\endgroup$ – Aditya Agarwal Sep 17 '15 at 10:48
  • $\begingroup$ Can you please mention where from (which website or book)you got the above version of Lenz's Law? Because the law seems to deviate from the original law stated by Lenz. The statement "the reason is inertia" is not totally true. $\endgroup$ – SchrodingersCat Sep 18 '15 at 15:31
  • $\begingroup$ My teacher told me that. "Due to inertia, the coil doesn't want to move and mass of electrons is very light, so they move in such a direction such that an opposing magnetic pole is formed on that side of the coil. $\endgroup$ – Aditya Agarwal Sep 18 '15 at 15:50
1
$\begingroup$

Aditya, a comment would have been enough perhaps. But I want to end the matter here. So here is a detailed answer.

As for your first question, my second comment must have proven it to be quite irrelevant. I believe you took your teacher too seriously (when he/she mentioned about the "inertia") without checking the Law in detail. I am putting up the comment which serves as my answer and I quote:

Your reasoning is correct but it is a trivial point and moreover it is NOT the law. The law is a direct consequence of the principle of conservation of energy. As you move the magnet, you do some work and the magnetic flux through the coil changes.This work done is manifested in the form of an induced EMF which causes a flow of current and produces a magnetic polarity, attracting or repelling, conserving energy.

So you see, inertia which forms a major part of your first question, is not that important. And the question becomes, to some extent, meaningless.

Now, as far as the second question is concerned, one thing to understand is that the galvanometer arrow gets deflected in the direction opposite to that of electron flow, i.e, in the direction of conventional current. That is how the instrument works- its working principle. Now if you ask me why, I will say you should go and consult the following from any standard physics textbook:

  1. The derivation of the formula $$\vec F = i(\vec l \times \vec B)$$ that is the magnetic force acting on a wire due to some magnetic field.
  2. How the above formula is used to derive the relation for magnetic torque, that is, $$\vec \tau = \vec m \times \vec B $$
  3. And finally how the above formulae are used to deduce the expression for the working principle of a galvanometer.The one I mentioned in the comment- $$ϕ=(\frac{NBA}{k})i$$

If you study these in detail, you will have no doubt that there is no right or wrong direction for a galvanometer arrow...its just that it is made in such a way that it depends on the direction opposite to that of electron flow, i.e, in the direction of conventional current.

P.S. I don't understand why the galvanometer is showing right or wrong direction, i.e. when the magnet is inside, South polarity is induced on the left side of loop and the reverse on the right side. So if you draw the direction of current, it flows from left to right. As the magnet is tried to be removed the induced emf opposes and so the direction of current changes and so does the deflection of galvanometer. And it is not clear on which side of the wire the +ve side of the galvanometer is connected. So nothing can be said about the direction in particular. If the connection is reversed, the deflection is also reversed.

I hope I cleared your doubt.

|cite|improve this answer
$\endgroup$
0
$\begingroup$

I'm not entirely sure what the question is. I can only suggest that perhaps you're confused at to which direction the electrons flow. Electrons flow in the opposite direction to the conventional direction of current flow, and everything else makes sense as far as I can see.

|cite|improve this answer
$\endgroup$
  • $\begingroup$ I am asking that why does Lenz law use conventional current's direction, when in real electrons move and that too, in the direction, reverse of conventional current. $\endgroup$ – Aditya Agarwal Sep 16 '15 at 9:10
0
$\begingroup$

According to the Faraday’s law of electromagnetic induction, emf gets induced in the rotor. As the rotor circuit is closed one so, the current starts flowing in the rotor. This currents called the rotor current. This rotor current produces its own flux called rotor flux. Since this flux is produced due to induction principle so, the motor working on this principle got its name as induction motor. Now there are two fluxes one is main flux and another is called rotor flux. These two fluxes produce the desired torque which is required by the motor to rotate.

In 1831, while pursuing his experiment, Michael Faraday made one of most important discoveries in electromagnetism. Now known as Faraday’s Law of electromagnetic induction, it reveals a fundamental relationship between the voltage and flux in a circuit.

|cite|improve this answer
$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.