# Tag Info

## Hot answers tagged electricity

41

Cracks and other flaws can be found in metal parts by scanning the surface of the part with a small electromagnetic coil, which induces a current flow in the metal part as if the coil and the part were two coils coupled together in a transformer. the presence of a flaw like a crack in the part perturbs the flow of induced current and in turn upsets the ...

15

I understand that a watt is a unit of power (change in energy per unit time) that describes the rate at which physical work can be done Right. The key thing to observe is that energy can move in both directions. It can move from the "supply" to the "load", but it can also move from the "load" to the "supply". The power at any given instant is found by ...

11

What you understand is basically correct. Regarding DC circuits it is important to point out that 1 watt = 1 amp x 1 volt under steady state (long time) conditions when transients are gone. Under those conditions an ideal capacitor looks like an open circuit (no current flow) and an ideal inductor looks like a short-circuit (no voltage across the inductor). ...

4

Drift velocities in metals are low, also in superconductors, typically less than 1 mm/s. But self-induction may cause a spark if you cut the circuit. And that does not depend on superconductivity.

3

Suppose I had a magnet coil in a fictitious AC circuit, that is purely capacitive, with no resistive component at all. It would exhibit purely reactive power flow. Wouldn't the coil produce a changing magnetic field, that I can use to deflect a nearby magnet The coil should have a purely inductive impedance (not capacitive), only it it were ideal, like an ...

3

First, don't do that. Ever. Seriously, you can injure yourself or others or start a fire. Second, DC motors are typically rated for around 10 V. That means that they have fairly low resistances. Your AC outlet probably operates at about 120 V if you are in many countries or even more in some countries. That means you are overloading the voltage capacity by ...

2

I know a battery maintains a potential difference between it's terminals , let's say that the ground is at 0 potential for my question , then with respect to the ground both the terminals are at non-zero potentials. This statement depends on what you mean by "ground". In electrical power systems "ground" refers to the earth, or "earth ground" because most ...

2

It is not clear from the question as to the output voltage of the AC power outlet but even it was $10\, \rm V$ there is good reason as to why the dc motor would overheat and be render useless in the process. When a dc motor is operating correctly the current through the motor does not only depend on the supply dc voltage and the resistance of the coil as ...

1

At each point on line $AB$ there are two forces on a positive test charges; a repulsive force due to the positive dipole charge and an attractive force due to the negative dipole charge. Both forces have the same magnitude and inclined by the same angle relative to the line $AB$. This means that the net force on the test charge is at right angles to the line ...

1

Of course, it is 0. And it is true that, if you place a third charge in that midpoint, that charge will move towards one of the ends, depending on the sign. If the extra charge is possitive, it will move towards the negative, of course. That is because the electric field is not 0. Charges move according to forces. Well, to be precise, charges can move ...

1

This is just a phase shift, and it can be done away with using a suitable redefinition of the origin of the time axis. For calculating the frequency it is irrelevant - you can completely disregard it.

1

No, you can't and here is why: In an ideal step-up transformer, as you step up the voltage, you step down the current. This means that the input power (input current times input voltage) equals the output power (output current times output voltage) and you therefore cannot create more power by sending it through a step-up transformer.

1

Everything is already explained in depth, and I want just attempt to say a few words about different units in everyday usage: Watt (W) is used to characterize [useful] power at consumer side; kWh measures actual energy used Volt x ampere (VA, VAR) is used to characterize transmission effects; kVARh measures energy transferred over power lines (in both ...

1

If i have an ordinary electric circuit with only one resistor, then if i raise resistance, the electric current goes down. As I understand it happens because the vector $\vec{E}$ of elecric field inside the conductor goes down. It depends if you changed the resistance by changing the effective length of the resistor or by changing the cross-sectional area ...

1

The 4 point resistance measurements are valid for any thickness. What your article is talking about are measurements of sheet resistance, which is a property that can be used to calculate resistance of other geometric shapes made of the same film. The equations they use presume that the thickness of the film is negligible compared to the distance between ...

1

According to the physics of electrical systems, no, not really. The line and the area around the line may be a couple of degrees warmer, but this is not the reason they do it. According to the Audubon Society, there are 3 reasons for birds to sit on telephone and power lines. It allows them to see their surroundings and keeps them safe from most predators ...

1

It is possible to generate both positive and negative static electric charges by rubbing (or even just contact). This is known as the Triboelectric effect and the list of materials involved is the Triboelectric series. Plastics tend to become negatively charged when rubbed and glass becomes positively charged. Once the two materials are separated the ...

1

In your question, $Id\vec{l}$ is along the z-axis. If a vector is perpendicular to this vector it means that it has to lie in the plane perpendicular to it and cannot have a component in the z direction. Put in equations, Let $$\vec{B} = B_x \;\hat{x} + B_y\;\hat{y}+B_z\;\hat{z}$$ Since $I\vec{dl}$ is along the z-axis, let, $$I\vec{dl} = I\;dl\; \hat{z}$$...

1

The metals conduct electricity because they have a high concentration of "free" electrons in them. These free electrons exists even in absence of current, they don't need to be sent or injected into the metal. Water does not have free electrons. All electrons are bound to water molecules or to $OH^-$ ions. In electrolites there are other ions but still no ...

1

I try to explain a little with informal language; the deep truth is: it's very complicated. If you manage to understand what really the electrons do, well you can get immediately a job in the huge battery industry/R&D. Sorry I'm no battery expert, I write the following from general electromagnetism knowledge. Yes in the galvanic cell we can somehow say ...

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