Sunday, April 22, 2012

Voltage, Resistance, and Current

Voltage, Resistance, and Current are three fundamental components to electric circuits that our technologically savvy world has been built on. They are responsible for all of the technology we take for granted today and luckily are closely related with one simple equation, called Ohm's Law.

 I (amps)= V(volts) / R(ohms)    ~this is Ohm's Law

V=IR is alternative form of Ohm's Law.


    Voltage measured in volts, is an electromotive force (EMF) or potential difference in electrical energy. Electrons move incredibly fast and in incredibly random fashion, but when a potential difference is present from one area to another then an electric field has been established which will slowly drift the zillions of electrons across a wire or other medium. The voltage or potential difference is responsible for current moving in direct current circuits.
     When you buy batteries for your TV remote, cell phone, and flashlights you are usually looking for a specifically sized battery, but more importantly an accurate number of battery cells to create the voltage demanded by the component that will use them. For example, AA batteries have 1.5 volts. So, the potential difference across the terminals of the battery is 1.5 volts. Most circuits require more than 1.5 volts, that is why most appliances, toys, remotes, use 4 (6 volts), 2 (3 volts) and sometimes 6 (9 volts). In most circuits, the voltage source is constant like how resistance is a constant  opposing force to the flow of current.

Volts, the unit for measuring voltage is symbolized with a lower or uppercase: v = V = volts. Voltage is sometimes symbolized with a E in equations to avoid conflicting with the voltage unit symbol, V or v.

Equations Related To Voltage
V = I / R      ~Ohm's Law
voltage (v)= current (A)/ resistance (Ohm)

P = I x V
Power (Watts) = current (amperes) x voltage (volts)

Electric Potential vs Electrical Potential Energy!


These are different types and sizes of resistors. 

Resistance, measured in ohms, resists the flow of electrons as they travel from high to low electric potential regions of a circuit. Resistance is present in any and every object you can think of, but in the case of most metals, the resistance is very close to 0 ohms, thus a great conductor of electricity. Before the transistor (transforming resistor) was invented, resistor values were always constant, regardless of the current of voltage they were opposing. However, the transistor (transforming resistor) allows the resistance from its pins to change value depending on an input current. For more on transistors go to my post, "Transistors Should Be Easy!"

Resistors are electrical elements used to establish a higher value of resistance in a circuit. For example, you should never hook a 9V battery to an LED (light emitting diode) because it would explode. You need a resistor to limit the amount of current reaching the LED (light emitting diode). Resistors in series add up to create higher amounts of resistance on a specific part of a circuit.

More resistance = more ohms = less flow of electronics =  less amperes of current

Equation for Resistance
R = V/I
R - resistance (ohms: Ω)
V - voltage (volts: v)
I - current (amperes: A)

Resistance of a wire
R_wire  =  (ρ * l ) /A
A - cross sectional area of wire
l - length of wire
ρ - resistivity

Resistors in series
Rtotal = R1 + R2 + R3 + Rn


Current (I : amperes)
Current, or the flow of charge, is measured in Amperes (A), and is symbolized with a capital "I" in equations and formulas, alike. Current can be thought of as voltage/resistance in almost all respects. One Ampere is equivalent to a one coulomb/second. So you can also describe electric current in terms of coloumb per seconds.

The "I" stands for Intensity of electric current, because an ampere is about six quintillions of electons traveling through a point of conduction per second. The "I" also avoids conflict of current with C which stands for specific heat, and also similarly could imply Celsius.

Equations Related To Current
I = Q / t
Q - electric charge (coulombs: )
I - current (amperes)
t - time (seconds) 

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