# 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 (Ω), 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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