inductor.

Not sure where you got the 4*pi/10,000,000 term, the equation for inductance is

L=(mu*A*N^2)/length

So, yes, the equation is correct but you are completely missing the point being made

OutToLunch said:

Not sure where you got the 4*pi/10,000,000 term, the equation for inductance is

L=(mu*A*N^2)/length

So, yes, the equation is correct but you are completely missing the point being made

Click to expand...

You say that the formula is correct, but on the other hand you say that the inductance depends on the magnetic field.
Where do you see 'B' in the formula?

Isnt it like saying that capacitance depends on electrical field?

you have been referring to a variable inductor and how a traffic light system detects the car through that variability. The magnetic field is altered because the car has entered into a region where it can affect the permeability of the loop inductor. This is the point: the only way that has any meaning at all is if there is current flowing through the loop for the system to detect a change.

allegro said:

So this formula is wrong?

H = (4 * Pi * #Turns * #Turns * coil Area * mu) / (coil Length * 10,000,000)

Click to expand...

"mu" is relative permeability, permeability is the ratio of the B field (flux) to the H field (vector potential). If you want to make a sticking point of it, you are trying to define a ratio of 0/0 by insisting on a definition with no current present.

Isnt it like saying that capacitance depends on electrical field?

Click to expand...

It does when you ask how goofing with the dielectric affects capacitance when there's no electric field.

It's like asking how a balance scale changes if you put a bigger rock on one side with the condition that there's no gravity.

But an inductance of an inductor is a physical quantity, that doesnt depent on the outside world or external sources (like current).

I dont understand, mu is the permabilty of the material that is inside the coil, isnt it?
If it is, so how come a car that is outside the coil, affects the inductance of the coil?

mu is the (relative) permeability of the material that "conducts" the magnetic field. The magnetic field surrounds the wires and when the car enters into this field it changes the permeability.

UM... would that circuit be similar to that of a simple metal detector?
it has a base frequency and you know when something metalic is near the magnetic field by hearing that base frequency drift in response to the change in the inductance value of L in the LC tank circuits resonance point?

There are three values for µ

allegro said:

So this formula is wrong?

H = (4 * Pi * #Turns * #Turns * coil Area * mu) / (coil Length * 10,000,000)

Click to expand...

OutToLunch said:

Not sure where you got the 4*pi/10,000,000 term, the equation for inductance is

L=(mu*A*N^2)/length

Click to expand...

duffy said:

"mu" is relative permeability, permeability is the ratio of the B field (flux) to the H field (vector potential).

Click to expand...

There are three values for µ (MU):

µ0 (mu zero) is the permeability of the vacuum. Its value is 4*pi/10,000,000 Henry / meter.

µ (just mu, without any subindex) is the permeability of a material. This is the ratio of the B field to the H field. It is also measured in Henry / meter

µR is the relative permeability of a material. Is the ratio between µ and µ0, or "how many times the material is more permeable than a vacuum". Typical values for steel are arround 1000 times.

1. My question is, if you do not apply current on the coil, but you place a car above the coil, would its inductance change?

Yes.

2. Now, if you place a car inside the (huge) coil, and still dont apply current on coil, would its inductance change?

Yes.

allegro said:

But an inductance of an inductor is a physical quantity, that doesnt depent on the outside world or external sources (like current).

Click to expand...

You claim to be "interested knowing whats right" but you sure aren't putting much effort into it. Weight is a physical quantity, right? But it's mass times the acceleration of gravity - no gravity, no weight. Gravity doesn't change the mass, but the weight floats without it and a scale won't work anymore than inductance will without a current.

Tell me - even if the car was inside the coil, would the coil necessarily be touching the car? It wouldn't. So what's the difference, above and not touching, or inside and not touching? You can't ignore that field. The field extends outside the coil. The car's still in the field when it's above it. If there's no field, then the coil is just a hunk of wire.

I don't understand why you are stubbornly and tediously refusing to acknowledge that field, unless maybe you're a troll here to jerk our chains.

If a tree falls in the middle of the woods and there is no one there, does it make a sound?

If a man says something in the forest, and there's no woman to hear him, is he still wrong?

Not fixed in 20 years!!!!

Dean Huster said:

The worst thing about traffic lights are the pinheads that program them. You should see the traffic lights in Poplar Bluff, Missouri. We have around 15 right now with a new one being installed within the next few months and no two have similar programming, so a vistor has no idea what's going to happen next. Needless to say, it isn't the biggest town! The next-largest town south of us has one light.

Dean

Click to expand...

Here I Loudon, Tn (37774) we have a traffic light at the intersection of Hwy 72 & 11 that has been operating on the backup timer for around 20 years! Most of the road sensors are bad but the city won't spend the money fixing them.
In the meantime the traffic has increased many hundred percent and and we have had periods of super high gasoline prices.

This is about the only way I can think of embarrass the city officials to do something. Talking to them is absolutely useless.

Rolf

I will gladly trade you a new roundabout for that old half-assed stoplight.