Current and Voltage

Current is the amount of charge per unit time passing a point. In a case, we have electrons moving past the point, and the Charge is ΔQ and the amount of time it has taken is Δt. The charge is ΔQ/Δt aka dQ/dT, which is the charge moving past the point in time.

We're going to move charge through a conductor and that's all current is. 1/10th of an amp can kill a person so an amp is actually a lot of current. Conventional current is the lack of electron holes, and conventional current is not the electrons moving but the holes moving in another direction. Voltage will go from the positive sign to the negative sign. Conventional current has the electrons moving in the opposite direction but the holes are moving from the positive to the negative direction. 

What's inducing the current is a voltage.  When it comes to current, I have no frame of reference. A single gate might be 10nA of current, whereas a computer has 5A of current and a hairdryer has around 10A of current. Digital TTL chip means that the gates can oppose the transistors. Most gates are CMOS gates but TTL chips are good for 5V devices such as Arduino Uno (35 mA or something like that). Quiescent current, or IQ, is the current drawn by a system in standby mode with light or no load. Power is voltage x current. So current is Power / Voltage. In the USA most socket support 10-20A and a hairdryer is just a heating motor, for about 1,000 Watts. 120V rms is standard voltage for the USA.

Voltage is really a manifestation of an electric field, between 2 conductive plates. When we put an electron inside of an electric field, there's going to be a force on the electron. First thing we need to create is that when you put a charge in an electric field, there will be a force exerted through the charge. Voltage is the "Pressure" that will help to move the charge, derived from the electric field. Call this charge Q0. We are changing the charge's potential energy denoted as U. 

Voltage is the potential energy per unit charge or mathematically V = U/q0 therefore the change in voltage is the change in potential energy per unit charge. dV = dU/q0 

1V = 1J/1C. What this means is 1 Joule of energy  must be used to use 1 Coulomb of charge to go across a potential difference of 1 Volt. Magnetic field and photoelectric effect can generate a voltage. 

There are 2 types of batteries: primary batteries and rechargeable batteries. There are chemicals inside of a battery that will generate a chemical reaction that creates a voltage difference. They are actually pretty easy to make. Most of these are standard consumer batteries, aka car batteries. 

The positive part of the battery is the anode and the negative part is the cathode. Here's the symbol: 

The positive side of the battery is the bump. The second you put a load on the battery the voltage is going to drop a little bit. These batteries have a bit of internal resistance. mAH represents amount of energy to do. 2400mAh means that the battery can supply up to 2,400 milliamps for an hour or we can do around 240 mA for 10 hours. 

The amount of energy is directly proportional to the size o the battery. In a 9V battery, the big circle is negative while the small one is positive. Switching leads in a multimeter will go to the negative sie. The red should be Voltages and the black should be on the COM feature of the Volt Meter. To measure current, we have to put the meter in the circuit put the meter into current mode. Put it on mA first. Now when we have the battery, it's got an internal impedance or internal resistor. A negligible voltage will drop across the battery. However, as we draw a lot of current, some voltage will drop across the internal resistance of the battery. 

To measure the current, we are going to put the meter in Amp mode and read what the current i is. The battery is going to push out a lot of crurrent, go through the meter, and the current i is the voltage drop over the resistor. If we pulled out 1 Amp of Current, then 1 Volt would drop over a 1 Ohm resistor. So to take another volt meter we will see how many volt is left using an internal impedance. 

0L in a voltmeter means it's out of range. If you measure current directly, the internal impedence is dropping a voltage and the battery gets hotter and hotter. So this means we can only measure current for a few seconds. Measuring the current directly will blow the fuse. What we have to do is to break the circuit and bridge the gap in the ciruit using the meter. To measure current with Ammeter, you HAVE to put the meter as part of the circuit itself.