## Ohm´s law

The most commonly used formula in electrical engineering is known as Ohm´s law. The law describes the relationship between Voltage (U), Resistance (R) and Current (I). Many law´s and formulas are important to remember but Ohm´s law is the formula that **every** electrical engineer knows by heart!

Ohm´s law states that U = I * R.

The picture above displays a basic DC circuit. Once the + side of the power source E is connection to the – side using a conductive material (Cooper wires for instance) an electrical current (I) will start to flow. The magnitude of the current will be dependent on the potential difference (Voltage) of the power source and the resistance in the circuit. By applying Ohm´s law it can be established that if a 12 V battery is connected to a 24 Ω resistor the current in the circuit will be 0.5 A.

*U = I * R *

*I = U/R*

*I = 12/24*

*I= 0.5 A*

## How does the circuit behave?

When analyzing a circuit the observer should acknowledge that current flows from the + side (cathode) to the – side (Anode). In the exact moment that a connection is made between the two potentials of the power source, a current will start to move in **all parts** **of the circuit at the same time**. It does not start at the + side but everywhere in the circuit simultaneously. The same amount of current that flows out from the cathode comes back to the anode. When current flows through a resistor there will be a voltage drop over the resistor. If the circuit is open there will be no current going through the component and no voltage drop over the component.

If two potentials are connected without any resistance or the resistance is extremely low, a situation will appear that is known as a short circuit. A short circuit will heat up the conductors and potentially cause fire´s, explosions or failures. A protective measure to avoid this scenario is to add a fuse to the circuit which will in the unfortunate event of a short circuit break the connection between the two potentials.

## In summary

- Ohm´s law describes the relationship with current, voltage and resistance in a electrical circuit
- Ohm´s law ==> U = I * R or I = U/R or R = U/I
- Current flows from the + side to the – side
- The current flow starts simultaneously in all parts of the circuit
- If a power source is connected without or very little resistance (Load) a short circuit is created (Not good)

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