2022-10-11 11:30:05 +01:00
|
|
|
---
|
|
|
|
|
tags: [physics, electricity]
|
|
|
|
|
---
|
|
|
|
|
|
|
|
|
|
# Resistance
|
|
|
|
|
|
2024-02-02 15:58:13 +00:00
|
|
|
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.
|
2022-10-11 11:30:05 +01:00
|
|
|
|
2022-10-23 13:30:04 +01:00
|
|
|
## Relationship between _resistance_ and _insulation_
|
|
|
|
|
|
2024-02-02 15:58:13 +00:00
|
|
|
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.
|
2022-10-11 11:30:05 +01:00
|
|
|
|
|
|
|
|
## Factors affecting resistance
|
|
|
|
|
|
2024-02-02 15:58:13 +00:00
|
|
|
- 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.
|
2022-10-11 11:30:05 +01:00
|
|
|
|
|
|
|
|
## Notation and scientific expression
|
|
|
|
|
|
|
|
|
|
### Resistance
|
|
|
|
|
|
2022-10-23 14:30:04 +01:00
|
|
|
- We use $R$ to represent resistance
|
2022-10-11 12:00:05 +01:00
|
|
|
- The unit of resistance is **ohms** ($\Omega$)
|
2022-10-11 11:30:05 +01:00
|
|
|
|
2024-02-02 15:58:13 +00:00
|
|
|
> One ohm is the resistance of a circuit or circuit element that permits a
|
|
|
|
|
> steady current flow of one
|
2024-02-17 11:57:44 +00:00
|
|
|
> [amp](Current.md#formal-expression)
|
2024-02-02 15:58:13 +00:00
|
|
|
> (one coulomb/second) when one
|
2024-02-17 11:57:44 +00:00
|
|
|
> [volt](Voltage.md#voltage) is
|
2024-02-02 15:58:13 +00:00
|
|
|
> applied to the circuit.
|
2022-10-11 12:00:05 +01:00
|
|
|
|
|
|
|
|
### 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
|
|
|
|
|
|
2024-02-02 15:58:13 +00:00
|
|
|
> Given that resistance is the opposite of conductance, the relation between the
|
|
|
|
|
> two quantities can be expressed via a recipricol: $R = 1/G$ and $G = 1/R$
|
2022-10-11 12:00:05 +01:00
|
|
|
|
2022-10-24 10:30:04 +01:00
|
|
|
## Ohm's Law
|
|
|
|
|
|
2024-02-02 15:58:13 +00:00
|
|
|
The relationship between current, resistance and voltage is expressed in
|
2024-02-17 11:57:44 +00:00
|
|
|
[Ohm's Law](Ohms_Law.md).
|
2022-10-24 10:30:04 +01:00
|
|
|
|
2022-10-23 14:30:04 +01:00
|
|
|
## Resistors
|
|
|
|
|
|
2024-02-02 15:58:13 +00:00
|
|
|
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.
|
