# Current and Resistance

Conventional Current vs Electron Flow

Tip: This isn't the place to ask a question because the teacher can't reply.

## Key Questions

flow of charge

#### Explanation:

Materials in general can be as classified as conductors, semi conductors or insulators depending on the behaviour of charge carriars when a potential difference is applied across it.
In metals for example, the charge carriars are the electrons. Experiments reveal that electrons move randomly in a conductor, but when a PD is applied across it the electrons gain energy and move in a particular direction.
The movement of these charge carriars constitute electric current;

Electrical resistance is the repulsion of a current within a circuit.

#### Explanation:

It explains the relationship between voltage (amount of electrical pressure) and the current (flow of electricity). With more resistance in a circuit, less electricity will flow through the circuit.
Electrical resistance shares some conceptual parallels with the notion of mechanical friction. The SI unit of electrical resistance is the ohm (Î©), while electrical conductance is measured in siemens (S).

$V = I \cdot R$

#### Explanation:

Ohm's Law states that the electric potential (Voltage) is equal to the electric current times the resistance.

$V = I \cdot R$

Another way to think of this is how to increase the current (or flow).

To increase the current, we need to increase the voltage and/or decrease the resistance.

Example, find the current in a simple circuit that has a $12 \text{V}$ battery and a wire with a resistance of $1.2 \Omega$

$I = \frac{V}{R}$
I=(12"V")/(1.2Omega) = 10"A"

One way to remember the relationship between $V$, $I$ and $R$ is the $V I R$ triangle:

This can be read as $V = I \cdot R$ or $I = \frac{V}{R}$ or $\frac{V}{I} = R$

• A thicker wire (of the same material) has lower resistance.

Having a thicker wire means that the volume of conducting material has increased so there are more conduction electrons available.

A concrete example of this point would be consider the current that flows through a wire. Now take a second identical wire and set it parallel with the first. The current that flows through the parallel combination would be larger (by a factor of two). Therefore the resistance of that arrangement must be less than the single wire (half the resistance of the single wire).

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