66 lines
2.3 KiB
Markdown
66 lines
2.3 KiB
Markdown
---
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tags: [physics, electricity]
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---
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# Resistance
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- Resistance is opposition to the flow of [current](./Current.md).
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- Different materials have different levels of resistance. For example glass and
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rubber are excellent resistors whereas silver and copper offer little
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resistance to current flow.
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- We utilise **resistors** to control the flow of current in a circuit.
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## Relationship between _resistance_ and _insulation_
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Resistance and insulation are not the same thing although they relate to the
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same natural phenomena.
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Resistance is a property of an electrical circuit whereas insularity is a
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property of substances found in the world.
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Similarly, insulators are naturally occuring materials that resist the flow of
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current to different degrees whereas a resistor is a man-made electrical
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component that is used to _control_ the flow of current in a circuit.
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## Factors affecting resistance
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- The larger the diameter of an electric wire, the lower the electrical
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resistance to the current flow. (If we use the analogy of electricity as
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water-flow: the wider the pipe, the more water that can flow.)
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- As a conductor heats up (e.g. copper, aluminium wire), its overall resistance
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increases.
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## Notation and scientific expression
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### Resistance
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- We use $R$ to represent resistance
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- The unit of resistance is **ohms** ($\Omega$)
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> One ohm is the resistance of a circuit or circuit element that permits a
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> steady current flow of one [amp](Current.md#formal-expression) (one
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> coulomb/second) when one [volt](Voltage.md#voltage) is applied to the circuit.
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### Conductance
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- We use $G$ to represent conductance
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- The unit of conductance is **Mho** (ohm spelled backwards) ($\mho$)
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> Conductance is the ability of a material to pass electrons
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> Given that resistance is the opposite of conductance, the relation between the
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> two quantities can be expressed via a recipricol: $R = 1/G$ and $G = 1/R$
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## Ohm's Law
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The relationship between current, resistance and voltage is expressed in
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[Ohm's Law](Ohms_Law.md).
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## Resistors
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A resistor is an electrical component that can be used in circuits to introduce
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specific amounts to resistance where needed. This is typically done in order to
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temper the total voltage and so keep the current flowing within certain set
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parameters.
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