Electricity

Potential Difference vs Electromotor Force

P.D is the energy provided to each charge within the circuit. It is also the difference in potential between two points. EMF accounts for the resistance within the battery it provides energy to the resistor in the battery.

where is EMF, is the resistance of the circuit and is the internal resistance of the battery.

The EMF of a cell is equal to the electrical energy per unit charge gained by the charges as they pass through the cell.

as the charges lose energy as they pass through the cell.

Coulombs

An electron has a charge of

Kirchoff’s Law

For any point in an electrical circuit, the sum of currents into a point is equal to the sum of currents out of that point.

Number Density

Number density is

It has unit In an insulator in a semi-conductor and in a conductor

Mean Drift Velocity

Electrons move at . Even though individually they move slow turning on a switch is instantaneous is as they push each other.

cross sectional area number density electric charge velocity

Derivation

volume

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Resistance

In a parallel circuit

An analogy is with traffic with more available lanes the flow of traffic increases.

Factors affecting resistance are: material, temperature, length and cross sectional area of wire

1. Length - the electrons will collide with more metal ions in total. Directly proportional
2. Cross sectional area - the electrons have more space to flow, more paths to go down.

where is resistivity - an intrinsic property of a material that measures how strongly a given material opposes the flow of electric current.

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Diodes

The diode circuit symbol shows the direction that conventional current can flow. In the foward direction the electrons still need a threshold voltage to pass through A diode is made of 2 layers. One consisting of positively charged particles p-type semi conductors, one with negatively charged particles. When electrons approach from the positive side the electrons are attracted to the positive particles and repelled by the negative making it hard for them to get through. When electrons approach from the negative side the negative particles repel the electrons through ??? TODO understand it properly