Electricity is the movement of electrons. Electrons create charge, which we can use to do work. Any electrical device uses the movement of electrons as a power source.

A circuit is a closed loop that allows charge to move from one place to another. Components are placed in the circuit to harness the movement of charge to do work.

Current, resistance, and voltage are three basic building blocks required to manipulate and utilize electricity. These cannot be seen, so tools such as multimeters and oscilloscopes have to be used to visualize them.

Voltage (ΔV) is the difference in charge between two points.

Current (I) is the rate at which charge is flowing.

Resistance (R) is a material's tendency to resist the flow of charge (current).

A water tank is often used as an analogy for voltage, current, resistance, and charge. In this analogy, water in the tank would be the charge. The water pressure would be the voltage. The amount of water flowing across a point on a pipe would be current. And a blockage or narrow section in the pipe would be resistance.

In the images below (from SparkFun), the water in the tank represents charge. The more water in the tank, the more pressure put on the water to move down through the pipe. Back in electrical terms, this would mean that a greater charge results in greater voltage. Furthermore, the water pressure (voltage) is going to impact the amount of water flowing out of the pipe (current). More pressure results in more water. Again, in electrical terms, more voltage will result in higher current. In the water tank, as the water level (charge) goes down, so will the pressure (voltage), resulting in less flow out of the pipe (current). This can be seen in flashlights as the batteries begin to die, the light will get dimmer until there is not enough charge to light the bulb anymore.

Resistance is neglected in the water tank analogy, but is a fairly simple concept to grasp. As mentioned above, resistance is the opposition to current flow. Wire and electrical components all have natural resistance in them, but they are negligible and will not be accounted for at this level. However, it is often necessary to use resistors in circuits to prevent to much current from entering a component. Imagine it this way, what would happen to your sink if you hooked it to a fire hydrant? It would be way too much water for your sink to handle. The same thing happens in electrical components. They can burn up from too much current flowing through them. Resistors are used to solve this problem.

Ω = Ohms

V = Volts

A or Amps = Amperes

ΔV = Potential Difference (Voltage)

I = Current

R = Resistance

W = Watts

R_T = Total Resistance

I_T = Total Current

ᐃV_T = Total Voltage

R₁ = Value of resistor 1

R₂ = Value of resistor 2

R_N = Value of the last resistor (no matter how many there are in the circuit)

V₁ = Voltage drop across resistor 1

V₂ = Voltage drop across resistor 2

I₁ = Current flowing through resistor 1

I₂ = Current flowing through resistor 2

I_LED = Current for LED

V_LED = Voltage required for LED

V_Batteries = Total voltage of batteries

Resistance (Series):

R_T = R₁+R₂+R₃+...R_N

Resistance (Parallel):

R_T^-1 = R₁^-1 ÷ R₂^-1 ÷ ...R_N^-1

* X-1 = 1/X *

** This provides you with the inverse of the total resistance **

*** Find the inverse of your answer to get total resistance ***

Total Voltage (Series):

V_Batteries = V_Battery1+V_Battery2+V_Battery3+...V_BatteryN

Excess Voltage:

V_Excess = V_Batteries - V_LED

Resistance Required:

R_Req = V_Excess ÷ I_LED

Required Wattage:

W_Req = V_Excess × I_LED

Series Circuits

Above, you can see an example of a simple series circuit. The image on the left shows a drawing of each component and the image on the right shows a schematic diagram of the same circuit. Series circuits have all components arranged so the charge can only flow in one direction. You can see in the illustrations above that there is only one path for electrical current to flow.

When working with series circuits, an important law to know is Kirchhoff's Voltage Law, which states that the sum of the voltage drops is equal to the applied voltage in a series circuit. This means that when you add the voltage drop across each component in a circuit, the sum should equal the voltage that is being applied to the circuit.

- More Coming Soon -

Parallel Circuits

Above, you can see an example of a simple parallel circuit. The upper image shows a drawing of each component and the lower image shows a schematic diagram of the same circuit. Parallel circuits have all components arranged so the charge will flow though multiple branches. You can see in the illustrations above that there are multiple paths for electrical current to flow.

When working with parallel circuits, an important law to know is Kirchhoff's Current Law, which states that the total current entering a circuits junction is exactly equal to the total current leaving the same junction. This idea by Kirchhoff is commonly known as the Conservation of Charge, as the current is conserved around the junction with no loss of current.

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Electricity Basics - Sparkfun

Direct Current - All About Circuits

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