Electricity and Magnetism
The electric potential difference (pd) between two points is equal to the work done (energy) required per unit charge to move from one point to another. It is also known as voltage (V).
Voltage is analogical to the differences of upstreams and downstreams where water flow in the stream is the flow of electrons within the circuit.
Resistors
A resistor is an electrical component which implements a specific resistance within an electric circuit.
A resistor with adjustable resistance is called a variable resistor.
Resistors can be connected in series or in parallel.
Kirchhoff's Laws
Voltage Current
The resistance of an object is proportional to its length (L) and inversely proportional to its cross-sectional area (A).
The resistance is influenced by the resistivity constant of the object (determined by the material it is made out of).
The existence of an electric potential difference (see the last section of 5.1) across an object causes charges to flow through the object.
Electric current (I) refers to the rate of flow of electric charge and can be given by the equation
The direction of an (conventional) electric current is opposite to the direction of electron flow.
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