AS Physics Unit 1.10 Resistance And Resisitivity Flashcards
What is the definition of Ohm’s Law?
Ohm’s Law states that the current through a metallic conductor is directly proportional to the applied potential difference, providing the temperature is constant.
What is the equation and units for resistance?
R = V / I
This is where R = resistance in ohms, V = potential difference in volts, I = current in amperes.
What are the two equations that link the power and resistance equations?
P = I^2 x R
P = V^2 / R
What is the current like in a series circuit?
It is the same anywhere.
What is the voltage like in a series circuit?
The voltage is shared across each of the series components.
What is the current like in a parallel circuit?
It is shared across each of the parallel components.
What is the voltage like in a parallel circuit?
It is the same anywhere in a parallel circuit.
What rate the two equations to add resistors in parallel?
1 / RT = 1 / R1 + 1 / R2
RT = (R1 * R2) / (R1 + R2)
What is the definition of resistivity?
Resistivity is defined as being the numerical value or the resistance between the two opposite faces of a 1m cube or material.
What is the equation and units of resistivity?
R = P x (L / A)
P = R x (A / L)
What are the units for resistivity?
Ohm meter (Nm)
What is 1mm^2 equal to in m^2?
1 x 10 ^ -6 m^2
What is the equation for the cross sectional area of a circle?
πd^2 / 4
What is the definition of a superconductor?
We can define a material as a superconductor if it loses all its electrical resistivity to become a perfect conductor when it is below its critical temperature.
What is the temperature that is known as absolute zero?
-273 degrees or 0K is absolute zero on the thermodynamic scale of temperature.
When was superconductivity discovered and what was the metal tested?
It was discovered in 1911 by a Dutch physicist and his experiment was about the resistivity of mercury.
What happens at -273 degrees or 0K?
All molecular motion ceases and metals have no resistance.
Where can we find superconductors in today’s world?
They can be found in MRI scanners and in Maglev (magnetic levitation) transport. This eliminates friction.
What happens as temperature rises for non-metals?
Resistance falls quite significantly.
Why does this happen in non-metals?
Non-metals have many more electrons in their outer shell that become available for conduction after thermal release.
What are semi-conductors at low temperatures?
Good insulators.
Why are semi-conductors bad insulators at higher temperatures?
As temperature increases their conductivity increases. They are said to have a negative temperature coefficient (NTC) of resistance.
What is one of the two things that can happen when the temperature of a metal is increased?
The outer shell or conduction electrons in the atoms can be released by thermal agitation.
What is the other thing that can happen as the temperature of a metal is increased?
The atoms begin to vibrate with both a greater frequency and larger amplitude. This means that the electrons have an increased chance of collisions.
