Electricity: EMF and Resistivity Flashcards
What is the equation for resistivity?
ρ = RA / l
What is the definition of resistivity?
A measure of the resisting power of a material to the flow of charge.
What is resistivity measured in?
Ohmic Meters (Ωm)
How does the length of a wire affect resistance?
A longer wire means a higher resistance.
How does the cross sectional area of a wire affect resistance?
A wider wire means a lower resistance.
How do semiconductors work?
Semi conductors work because electrons are held in bonds in-between the atoms. Once a few electrons have enough thermal energy to escape from these bonds they conduct electric current. As temperature increases, more and more electrons get the ability to conduct electricity. This causes the semiconductor to become a better conductor as temperature increases.
What is superconductivity?
A property that causes a material to have zero resistance once it reaches the critical temperature.
What are the advantages of superconductors?
You can send current a very long way.
Current doesn’t produce any heat.
Can produce strong magnetic fields.
How do we find the total resistance in series?
Rₜ = R₁ + R₂ + R₃ …
How do we find the total resistance in parallel?
1/Rₜ = 1/R₁ + 1/R₂ + 1/R₃ …
What is Kirchoff’s 1st law?
The sum of the current entering any point in a circuit is equal to the sum of the current leaving that point.
(Total current INTO a junction = Total current OUT OF a junction)
In a simple series circuit, how does current behave?
Current will be the same at all points in the circuit.
In a parallel circuit, how does current behave?
Current will split at junctions and recombine later.
In a simple series circuit, how does potential difference behave?
Voltage is shared between the components in a series circuit.
In a parallel circuit, how does potential difference behave?
When voltage reaches a junction, it doesn’t change in either path.
How does a multiple cells connected in series behave?
Potential difference increases but current doesn’t change.
How does a multiple cells connected in a parallel circuit behave?
Current increases but potential difference doesn’t change.
What is Kirchoff’s 2nd law?
The algebraic sum of the directed potential differences in any circuit loop is zero.
How do we calculate energy?
E = IVt
Name 4 different power equations
P=IV P=W/t P=I²R P=V²/R
What is a potential divider circuit?
A circuit used to supply constant or variable potential difference from a power supply.
How does a potential divider circuit work?
Two fixed resistors in series can provide a known fraction of a given potential difference. If you change one of the resistors, then you can increase or decrease the voltage.
What’s the definition of EMF?
EMF is the power supplied per unit current.
What are 2 ways we can calculate EMF?
ε = E/Q OR ε=I(R+r)
What’s the definition of internal resistance?
Opposition to the flow of charge within the battery.
What is terminal potential difference?
Potential difference measured across the terminals of the power supply. (The output of the cell)
How do we calculate terminal potential difference?
V = ε - Ir
How do we calculate efficiency?
Efficiency = (Power in Circuit / Power produced by cell) x 100
