Physics - Resistivity
What three things does the resistivity depend on?
- The material of the wire.
- The length of the wire.
- The cross-sectional area of the wire.
If you double the length of a wire, what happens to the resistance?
It also doubles.
What’s the difference between resistivity and resitance?
Resistivity is the property of a material whereas resistance is just a measurement of a component.
How would you write that the resistance $R$ is directly proportional to its length $L$?
How would you write that the resistance $R$ of a wire is inversely proportional to its cross-sectional area $A$?
If $R \propto L$ and $R \propto \frac{1}{A}$, how could you combine these equations?
\[R \propto \frac{L}{A}\]
How would you write this using a constant of propotionality?
\[R = \frac{\rho L}{A}\]
What does $\rho$ represent in this equation?
The resistivity.
What are the units for resistivity?
What does the gradient of this graph represent?
What does the gradient of this graph represent? How would you work out the resistivity from the gradient?
How would you work out the resistivity from the gradient?What factor is not accounted for in the resistivity equation?
Temperature.
What experiment could you perform to determine the resistivity of a material?
Measure how the resistance of a wire varies with its length.
Roughly, what’s the order of magnitude for the restivity of conductors?
How can you keep the current constant as you change the length of a wire?
Use a variable resistor in the circuit.
Why is it important to keep current constant in an experiment measuring resistance?
Because changing the current will affect the temperature of the wire, which will also affect the resistance of the wire.
What does it mean for a component to be a super conductor?
The material has no resistance.
What is the current issue with superconductors?
They have to be kept very cold.
What does $T _ c$ represent here?
What does $T _ c$ represent here?The critical temperature of the superconductor.