Electric Circuits Flashcards
Charge Definition
The property of the protons and electrons within an atom which experience a force within the electric field.
What is the charge of a single electron?
1.60 x 10^-19 C
What is charge measured in?
Coulombs / C
Charge in a series circuit….
is the same everywhere.
Charge in a parallel circuit…
sum of charge equals total charge.
Current Definition
Current is the rate of flow of charge from positive to negative terminal.
Current Equation
Current = Charge / Time
What is the Principle of Charge Conservation?
Total electric charge in a closed system does not change.
What is Kirchhoff’s First Law?
Total current flowing into a junction is equal to current flowing out.
What is current measured in?
Amps / A
In a series circuit current…
is the same everywhere.
In a parallel circuit current…
sum of currents equals the total current.
Potential Difference Definition?
The energy transferred per unit charge between two points.
Potential Difference Equation
Voltage = Energy Transferred / Charge
Potential Difference in a series circuit…
the sum of all the voltages is equal to the total potential difference.
Potential Difference in a parallel circuit…
potential difference is the same across each branch and sum to give total potential difference.
The sum of all voltages in series is…
equal to the battery voltage or sum of all the voltages is 0
Resistance Definition
A measure of how difficult it is for charge carriers to pass through a component.
Resistance Equation
Resistance = Voltage / Current
What is Ohms Law?
Ohms Law states that current is directionally proportional to current given that the conditions remain constant.
Resistance in a series circuit…
the sum of each resistor equals the total resistance.
Resistance in a parallel circuit…
the sum of the reciprocal resistances equals the total resistance.
Drift Velocity Equation
Current = number of charged particles x cross sectional area x velocity x charge
Power Definition
Rate of energy transfer over time
Power Equation
Power = Voltage x Current
How do you use power to find energy transfer?
Multiply power by time to find energy transfer.
EMF Definition
Energy transferred to a unit charge
EMF Equation
EMF = Energy Transfer / Charge
What is EMF measured in?
Volts / V
EMF Key Facts
Emf is the product of the total resistance within a circuit, it is the sum of P.D. in a closed circuit, EMF energy into circuit is equal to the P.D. out of the circuit.
What is internal resistance?
Resistance within a battery which is caused by electrons colliding with atoms inside the battery so some energy is lost before electrons leave the battery.
Internal Resistance Equation
EMF = Terminal P.D. + Lost Volts = Current (Load Resistance + Internal Resistance)
What would happen if there is no internal resistance?
The terminal P.D would equal the EMF.
What is terminal P.D.?
The voltage across the load resistor
What does a graph for EMF and Internal Resistance look like?
y - axis = Voltage, x - axis = Current, y - intercept = EMF and gradient = - Internal Resistance
What is a potential divider?
A circuit that has two or more resistors, that is series and when an output is placed across one of the resistors.
What are potential dividers used for?
It is used to predictably vary the proportion of a supply the output receives.
Potential Divider Equation
Voltage Out = Voltage In x Resistance 2 / Resistance 1 + Resistance 2
What can the variable resistor be replaced by?
A thermistor or LDR
Resistivity Definition
A measure of how easily a material conducts electricity.
Resistivity Equation
Resistance x Cross-Sectional Area / Length
What happens in an ohmic conductor?
In an ohmic conductor as you increase P.D. the energy transferred to each electron increases so they collide with greater force increasing drift velocity. This means that current increases as I = nAqv and V is directly proportional to I. AS resistance is inversely proportional resistance is 1/R.
Example of an Ohmic Conductor
Wire or Resistor
What happens in a semi-conductor?
As current increases so does the temperature this means that the number density increases as more free electrons are released so resistance decreases however it does not obey ohms law a temp increases so P.D. does not increases proportionally.
Example of a Semi-Conductor
Thermistor and LDR
What happens in a Filament Bulb?
In a filament bulb as P.D. increases the energy of electrons increases so there is greater energy in collisions with ions. This causes temperature to increase so metal ions vibrate with a greater amplitude further increasing collision rate. The resistance increases and as temperature increases it does not obey ohms law V = IR so current does not increase proportionally.
What happens in a Diode?
The forward bias of a diode is the direction in which it will allow current to flow past the threshhold P.D. Above the threshold P.D. electrons move up an energy level to the conduction band so the number of free electrons increases and as I = nAqv current also increases.
