PHYSICS RESISTANCE Flashcards
What is the definition for potential difference?
Pd between two points is energy converted from electrical potential to another form per coulomb
What equation links energy transferred to charge and pd?
AE = VQ
V=W/Q
W=VIt
What is the definition for electrical resistance?
Resistance of a conductor is the pd across it divided by resulting current through it R=V/I
What causes electrical resistance?
Collisions between free electrons and positive ions in metal lattice transter energy
What does a current-voltage graph for a wire at a constant temperature tell us about the resistance?
Constant resistance (straight line)
Draw a current-voltage graph for a filament lamp
Curve increasing at a decreasing rate
What does a current-voltage graph for a filament lamp tell us about the resistance?
At low voltage resistance is constant (straight line), as voltage and temperature increase resistance increases
What is the definition of Ohm’s law?
Current in a metal wire at a constant temperature is proportional to the pd across it
What does it mean if a device is non-ohmic?
Temperature increases and resistance increases (not constant resistance)
What is the definition of power?
Energy transferred per second P=E/t
What are 2 equations that link Power and Current?
P = I V and P = 1R
What is the resistivity equation?
R = pL/A
What is the unit of resistivity?
ohms
What effect does doubling the radius have on the resistance of the wire?
A=(pie)3.14*r so doubling radius means A x 4 so R decreases by a factor of 4
What is the definition of superconducting transition temperature Tc?
Temperature at which material loses all resistance and becomes superconducting
Give an example of a metal that exhibits superconductivity and one that doesn’t
Zinc/Lead/Mercury exhibit superconductivity but
Copper/Silver/Gold never do
What is the advantage of using superconducting wires?
No resistance so no heat loss (less power dissipated)
Give 2 applications/uses for superconductivity
Nuclear fusion reactors, Large Hadron Collider, Particle accelerators, MRI scanners, Large generators
What is the disadvantage of using superconducting wires?
Difficult to sustain extremely low temperatures, materials are often brittle and hard to make into a wire
