Resistance

  • Resistance is opposition to the flow of current.

  • Different materials have different levels of resistance. For example glass and rubber are excellent resistors whereas silver and copper offer little resistance to current flow.

  • We utilise resistors to control the flow of current in a circuit.

Relationship between resistance and insulation

Resistance and insulation are not the same thing although they relate to the same natural phenomena.

Resistance is a property of an electrical circuit whereas insularity is a property of substances found in the world.

Similarly, insulators are naturally occuring materials that resist the flow of current to different degrees whereas a resistor is a man-made electrical component that is used to control the flow of current in a circuit.

Factors affecting resistance

  • The larger the diameter of an electric wire, the lower the electrical resistance to the current flow. (If we use the analogy of electricity as water-flow: the wider the pipe, the more water that can flow.)
  • As a conductor heats up (e.g. copper, aluminium wire), its overall resistance increases.

Notation and scientific expression

Resistance

  • We use \(R\) to represent resistance
  • The unit of resistance is ohms (\(\Omega\))

One ohm is the resistance of a circuit or circuit element that permits a steady current flow of one amp (one coulomb/second) when one volt is applied to the circuit.

Conductance

  • We use \(G\) to represent conductance
  • The unit of conductance is Mho (ohm spelled backwards) (\(\mho\))

Conductance is the ability of a material to pass electrons

Given that resistance is the opposite of conductance, the relation between the two quantities can be expressed via a recipricol: \(R = 1/G\) and \(G = 1/R\)

Ohm’s Law

The relationship between current, resistance and voltage is expressed in Ohm’s Law.

Resistors

A resistor is an electrical component that can be used in circuits to introduce specific amounts to resistance where needed. This is typically done in order to temper the total voltage and so keep the current flowing within certain set parameters.

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