Section 6 (Electricity) - Resistance and Resistivity Flashcards
Definition of Resistivity:
The measure of how much a particular material resists current flow
If the area of the a wire increases, what happens to the resistivity?
The resistivity decreases as it’s easier for electrons to pass along it
If the length of the a wire increases, what happens to the resistivity?
Resistivity increases as it’s more difficult for current to pass through
Difference between Resistance and Resistivity
Resistance is a property of an object
Resistivity is a property of a material
What are Semiconductors?
A group of materials that aren’t as good as metals at conducting electricity. i.e. higher Resistivity.
(Because they have fewer electrons available)
What does the Resistance in a Thermistor (NTC) depend on?
What is the relationship between these two variables?
- Temperature
- As Resistance decreases, temperature increases. Therefore current increases.
What is a Superconductor?
A material which no longer has resistivity.
How can a material lose resistivity?
When it’s cooled down to below a critical temp called the ‘Transitional Temperature’.
Hard/Expensive to reach transitional temp as it’s very low (e.g. -250 °C)
No Resistance = No Heat Wasted
What are the uses of Superconductors?
Can be used to make:
- Power cables
- Strong Electromagnets (e.g. Maglev trains)
- Electronic circuits that work fast as there’s no resistance to slow current down.
Definition of Resistance:
The measure of how much a particular object resists current flow
Ohm’s Law states:
Current is directly proportional to Voltage in an Ohmic Conductor, IF physical conditions (temp) remain constant.
When there’s 2 resistors in parallel, to find Total Resistance you can use the formula…
Total R = (R1 x R2) / (R1 + R2)
