Question about galvanometers and coils...?

Question

Two separate but similar oils of wire are mounted close to each other. The first is connected to a battery and has a direct current flowing through it. The second is connected to a galvanometer. How does the galvanometer respond when the switch in the first circuit is closed? How about after being closed when the current is steady? And what about when the switch is opened?


*This is for my physics class.....I'm SO confused! If someone could explain it in easily-understandable terms, i would greatly appreciate it!

Answer 1

Not so clear question. It depends firstly on which polarity you hv connected ur galvanometer. It will determine the fluctuation of the galvanometer.
There should be a change in the current so that a deflection is noticed.

Answer 2

Okay, what you have here is a circuit set up to show inductance. What happens is, when the switch is closed that connects the battery to the coil, a current begins to flow.

The coil has some natural resistance to it (we are talking about normal wire conductors, not superconductors.) As the current beings to flow through the coil, it generates a magnetic field. At the same time, the magnetic field generates a voltage opposite in polarity to the voltage causing the current to flow through it.

[This is sometimes called a counter-EMF, or back-EMF. EMF is the abbreviation for Electro-Motive Force, the technical name for voltage.That is what motivates the electrons and forces them to move through the circuit as a current.]

So, the counter-voltage wants to cause a current to flow in the opposite direction. The total current flowing in the original direction is diminished by the magnitude of the current caused by the counter-EMF.

So, the current in the first coil starts at a maximum and dminishes to a steady-state value.

If we were to use an oscilloscope to look at the current as it increases from zero to its maximum value, we would see that it is not an alternating current (it does not periodically reverse direction) but it IS a changing current; changing from zero to its maximum value. Only a current changing (either alternating or from one value to another) can cause a changing magnetic field. Otherwise the magnetic field would be a single value all the time.

It is necessary to have a changing magnetic field to induce currents and voltages from one coil to the other. A magnetic field sitting at one level will not do the trick. Imagine the magnetic field expanding and contracting like a balloon that is being inflated and deflated. It takes up more or less space.

As the changing magnetic field passes over the other coil, a current is induced. This means that the changing current in the first coil caused a changing magnetic field, and the changing magnetic field caused a changing current in the second coil.

This is the basis for how a transformer works. This is how we can step voltages and currents up and down.

The galvanometer will deflect for a moment, only until the changing current in the first coil reaches its final value. If the current in the first coil was alternating, the current in the second coil would alternate as well.

[That is, if the current in the first coil was periodically reversing direction, dropping to zero, starting to flow in the opposite direction, then increasing to a maximum value, then decreasing back to zero and then flowing the other way again in a repeating pattern, the current in the second coil would mirror that behavior.]

When the current reaches its steady-state value in the first coil (a value limited only by the resistance of the coil itself), the current in the second coil drops to zero. The current in the second coil reflects not the magnitude of the current in the first coil, but the rate of change of current in the first coil.

Call the first coil the primary and the second coil the secondary. When the primary current has just been switched on, it is at its maximum. As the counter-EMF builds against it, it diminishes to the steady level. As the primary current changes, it induces a current in the secondary. When the primary current diminishes to the steady level, the current in the secondary diminishes to zero.

I hope this is clear enough for you. If not, try looking on line for an animation illustrating this. There must be some somewhere, and it is easier to understand with colors and moving arrows indicating the direction of the currents. Good Luck!

Answer 3

Prior to the switch being closed the Galvanometer is pointing to zero. When the switch is closed the Galvanometer needle will deflect in one direction, reach a max, and return to zero. While the current is steady the Galvanometer needle will point at zero. When the switch is opened the Galvanometer needle will deflect in the opposite direction than when the switch was closed. Again, it will reach a peak and return to zero.

Answer 4

From Wikipedia: The term "galvanometer" derives from the surname of Luigi Galvani. Many early purposes of galvanometers for measuring and recording are related with William Thomson (Lord Kelvin). The earliest galvanometer replace into stated via skill of Johann (Johan) Schweigger of Nuremberg on the school of Halle on sixteenth September 1820. André-Marie Ampère additionally contributed to this form of the galvanometer. i've got have been given now no longer been waiting to be sure if Schweigger's galvanometer replace right into a shifting coil or iron vane gadget. The physicist Johann Salomo Christoph Schweigger is outstanding typical because of the reality the inventor of a gadget for measuring susceptible electric powered currents, the so-referred to as multiplicator. From the 0.33 reference, it form of feels to have been a shifting coil gadget.