2024-12-09 18:34:15 +00:00
|
|
|
---
|
|
|
|
|
tags: [physics, electricity]
|
|
|
|
|
---
|
|
|
|
|
|
|
|
|
|
# Resistance
|
|
|
|
|
|
2025-01-16 07:08:09 +00:00
|
|
|
- Resistance is opposition to the flow of [current](Current.md).
|
2024-12-09 18:34:15 +00:00
|
|
|
|
|
|
|
|
- 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](Current.md#formal-expression) (one
|
|
|
|
|
> coulomb/second) when one [volt](Voltage.md#voltage) 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](Ohms_Law.md).
|
|
|
|
|
|
|
|
|
|
## 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.
|
