2. Circuits Flashcards
Definition of current
The rate of flow of charge
Current Units
Amps
Current equation
I = Q / T
Unit for charge
Coulombs
What equation do you use to figure out the speed of electrons in a conductor?
I = naVe
What does drift velocity mean
How fast each electron moves
What does the n stand for in I= naVe
Charge carrier density = number of electrons per meter
How to derive I = naVe
time = length / velocity
N = volume x charge carrier density
Charge of an electron = e
Definition of potential difference
The energy supplied per unit charge
Unit of Pd
Volts
Equation to find voltage
V = IR or V = E / Q
Definition of resistance
The ratio of potential difference to current
Equation for resistance
R = V /I
How does resistance occur
The collisions between free electrons and the ions means it is harder for electrons to flow
What happens when temp is increased within a conductor
Resistance increases as it is proportional to temperature
The kinetic energy of particles increases so particles are moving faster so they collide more therefore higher resistance and temp
What is ohms law
R is constant for all values of V and I
What is the equation for resisitivity
Resistance = (Resistivity x length) / area
What is resistivity
The general measurement of how much a material resists the flow of current
It stays constant for the same type of material
What is the unit for resistivity
Ohm - metre
What is the IV graph for a filament lamp
Curved starting from the origin
What is the IV graph for a metal wire at a constant temp
Directly proportional
What is power
The amount of energy transferred per unit of time
Power equation
P = IV or P = E/ T
What is superconductivity
When a material conducts with zero resistance
What is the transitional temperature
The temperature which a super conductor needs to be cooled down to
How are superconductors used
Used to create magnets used in trains
MRI scanners
Particle accelerators
What quantities are equal across branches in a parallel circuit
Potential difference
What happens to current in a parallel circuit
Each branch must add up to the current through the source
What is the difference between sum of resistance in a series circuit and in a parallel circuit
Series= resistors all add up
Parallel= Reciprocal of the sum of reciprocals
What is a potential divider
When there are two resistors in series
What is a potential divider used for
To supply a variable voltage to an external circuit
What is a thermistor
A temperature sensitive device that reduces resistance when heated
What is an LDR
Light dependent resistor
Made out semi conductor material they have a lower resistance when exposed to the lighyt
What happens when light intensity increases on a circuit with a LDR
The resistance of the LDR decreases so the potential difference also decreases
What is EMF
Electromotive force
Definition of emf
The energy supplied per unit charge from the source
What is the equation with EMF
V = E - Ir
What do you do when a series circuit has multiple cells
Add up all the emf and add up the internal resistance to make overall total of one cell
What is a diode
A component that only allows current to flow in one direction
What is Kirchoffs first law
All of the current going to a junction is equal to the total current leaving the junction
What is Kirchoffs second law
The sum of potential differences must equal the total emf of the circuit
