Ohms Law - PatternAgents/Electronics_One_Workshop GitHub Wiki

We're not going to get too heavy into the math here, but a basic understanding of the physics involved will help you to understand some the choices that need to be made in working with simple electronics. Consider the most simple Schematic Diagram, a single Resistor {R}, with an attached power source (i.e. a Voltage).

SimpleCircuit

  • The basic Schematic Diagram (shown above), depicts a Voltage {V} being applied across a Resistor {R}, causing a direct current {I} to flow from the positive (+) terminal through the Resistor {R} and to the negative (-) terminal.

  • The relationship between Voltage, Current, and Resistance is described by Ohm's Law, where:

    • Voltage (V) - electric potential (in Volts)
    • Current (I) - electric charge (in Amperes)
    • Resistance (R) - material opposition (in Ohms)

  • So, One (1) Ampere of Current flows when One (1) Volt of electric potential is applied across a resistance of One (1) Ohm

  • Many people find this easier to remember when visualized as a triangle:

ohms-law

1 Ampere = 1 Volt / 1 Ohm

Power (measured in Watts) is also a simple relationship between current and voltage

1 Watt = 1 Ampere * 1 Volt

Again, many people find this easier to remember when visualized as a wheel of triangles:

wheel-of-ohm

  • A practical application example? You just bought a new Toaster that the box says is 1600 Watts, and a new hot water kettle that the box says is 1200 Watts. When you try to use them both at the same time, your circuit breaker pops and needs to be reset, why? Well, circuits (wires and components) always have a maximum current rating - how much current they can safely handle before overload or failure. A typical domestic plug in your home provides 120 Volts at around 15 Amperes of current. So how much are we demanding with both units switched on at the same time ?

Toaster = 1600 Watts / 120 Volts = 13.333 Amperes

Kettle = 1200 Watts / 120 Volts = 10.000 Amperes

Toaster + Kettle = 23.333 Amperes

  • So, when you turn on both at the same time, you are demanding 23 Amperes of current from a plug that can only provide 15 Amperes of current; that causes the circuit breaker to trip, in order to prevent the wires from getting too hot and possibly melting or causing damage to your home wiring. So, either use them one at a time, or move them to separate circuits (i.e. different wires) that can provide 15 Amps to each appliance independently.

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