Anonymous
Anonymous asked in Science & MathematicsPhysics · 7 years ago

# Simple questions about electricity that I just can't understand?

Hello, my physics teacher wasn't very good, and therefore I can't study more complicated things since I don't fully understand the basics of electricity... I seem to understand things well if they are explained with examples and if someone tells me how it is used. If you only know an answer to just some of these questions, please answer anyway, even if one question is answered it will help a lot.

What exactly is voltage? How is it useful? If something has 12V, what does it do differently compared to something that has 1V? I read that it is like a force pushing the electrons through the wire, does that mean that in the US, the electricity is pushed slower since it has 120V compared to Europe's 220V?

What is the difference between DC and AC? How is each one used? How is it useful? I know that DC keeps flowing through the circuit, and that AC moves, stops, and moves the other way. Doesn't that keep the AC in one spot? How can that be used as electricity if it doesn't really move?

What is an inductor? How is it useful? how does it work? What does it do?

What does it mean when something "Induces". I understood it as it creates, but I just can't seem to fully understand.

Thank you for your help, I am generally good in physics, but electricity is something that I am bad at. Thank you.

Update:

So pretty much it is a force that pushes electrons through? So if I have 1V, it pushes through a certain amount, but if I have 12 V, it pushes through 12 times more electrons, meaning that the amount of electricity in ampers that passes is also 12 times bigger? So higher voltage, more electricity passing through?

Update 2:

Brendan: About AC: But how does the electricity get to my house if the electrons are essentially in the same position? Does it work like this: http://www.youtube.com/watch?v=0LnbyjOyEQ8

?

Relevance
• 7 years ago

Voltage is a measured potential difference in electic field applied to a charge. Essentially, it acts on charged particles in a similar way to how gravity acts on mass: it "forces" the charged particles to move along a path. Voltage itself is basically the total "distance" a charged particle can be made to travel within an electric field, as it is literally V = E*d (Voltage = Electic field applied over a distance). A voltage of 12V can mean an electric field of 12N/C (Newtons per coulomb, Force per unit charge) is applied over a distance of 1m, or it can mean that a field of 1N/C is applied over 12m. The important thing is the total of how much potential energy that voltage can contribute, which is actually directly measured as PE = Q*V/2 (Potential energy = 1/2 Charge times voltage). 120V doesn't necessarily means particles move "slower" it just means there won't be as many of them pushed through the wire at one time. It could be because they're slower or because there's fewer of them. Current is the measure of the number of charged particles moving through a conductor (wire), not necessarily the speed of them.

DC and AC are vastly different in both in practice and application. DC (Direct Current) simply means electrons flow from one way to the other. A DC circuit exhibits 3 stages: Initial, Intermediary, and Final (those aren't actual terms, but there are 3 stages). There is an intial stage, before a DC condition is met (flipping a switch, etc.), an intermediary (when components are adjusting to new values), and final stage (when things settle to their final values and stay that way). DC is very useful for a lot of consumer applications, such as charging a phone (need a constant voltage), running a computer (1's and 0's are represented through constant voltages, usually +5V for 1 and 0V for 0).

With AC, don't try to think of the particles as "not moving". At the end of the day, they haven't moved from their original spot, but they exhibit motion one way for a period of time, and then the other way. In doing so, they can cause components like capacitors and inductors to behave differently. AC is also extremely useful because this "lack" of motion means that your supply doesn't exhaust as much energy because the RMS (Root Mean Square) of the voltage is lower than its DC counterpart, thus it burns less energy in the power lines while being transmitted. As a result, AC signals are used by power companies to transmit the electricity to your house. If DC was used, you would need an enormous number of repeaters in power grids to make sure that the power stayed constant, and electricity in your home would cost significantly more as a result. AC is also the reason why transformers work, but I'll let you research that one. Basically, without AC, we would need to take power from the power company "as is", without it being stepped down. It is "ramped up" in the first place to ensure that there isn't too much power lost within the power lines themselves while being transmitted, since powerlines can act like enormous resistors.

Inductors serve many purposes: transformers, noise blockers, etc. It works by Ampere's Law, which states that an electric current flowing in a straight line will generate a circular magnetic field that flows in a rotating, perpendicular fashion around the line of current. They call this the right-hand rule, because if you stick the thumb on your right hand up (which represents the line of current), the rotation inward of your fingers tells you the direction that the magnetic field rotates around that line. In an inductor, you wind the wire in a coil, thus making the current into the circle, which adds all the magnetic field of the loops in the coil together into one giant magnetic field straight in the middle. When current flows through an inductor, it generates a magnetic field, and when the current within the inductor changes, this pre-existing magnetic field ensures that, at least for a short while, the current continues to flow in that same direction until all of its energy is burnt off, at which point it can no longer generate a current to oppose this change.

Induction is when the action of one part of a circuit/component causes another to behave in a direct manner. In the case of an inductor, the flow of current "induces" a magnetic field within it.

I hope this helps, I tried to be as thorough as possible. If you are still curious (which is never a bad thing), then there are literally limitless resources available on youtube and such. A great person for explaining a lot of these components is either Afrotechmods or Collin Cunningham on youtube.

• 7 years ago

It is not practical to answer all of your questions as there are so many. So I will just answer the first one.

Q1. What exactly is voltage?

The technical definition is that the voltage between 2 points is the electrical energy transferred per unit of charge passing between the 2 points. This leads to the equation V=E/Q, where V is voltage, Q is charge and E is energy transferred.

What this means is best explained with an example.

Suppose when 20 coulombs (20C) of charge pass through a bulb 100 joules (100J) of electrical energy are turned to heat and light energy. The voltage across the bulb is:

V = E/Q = 100/20 = 5 J/C

The unit 'joules per coulomb' (J/C) is called the volt, so the voltage across the bulb is 5 volts.

It is usually more convenient to think of voltage as a sort of 'pressure' pushing current around a circuit. If the voltage is increased the current is increased.