Electric circuits Flashcards
(24 cards)
Conventional Current Flow
Flow from positive to negative, used to describe the direction
of current in a circuit.
Current
The rate of flow of charge in a circuit, measured in Amperes and has symbol I
I=ΔQ/Δt
Diode
Components that allow current through in one direction. In the correct direction,
diodes have a threshold voltage
EMF
The energy supplied by a source per unit charge passing
through the source, measured in volts.
Internal resistance
+equations
The unavoidable resistance any power source will have that makes it
harder for current to flow through the source. It causes energy to be dissipated in the source. (Lost volts per unit current)
EMF =V+ Ir
EMF=I(R+r)
Kirchoff’s first law
The total current entering a junction is equal to the total current leaving
it
Kirchoff’s second law
The sum of EMF in any loop of the circuit is equal to the sum of the
potential differences of each component
Light dependent resistor
When these components are illuminated with light their
resistance goes down. As light intensity increases resistance decreases.
Ohmic conductor
A conductor following Ohm’s law where current flowing through it is
directly proportional to the potential difference between each end of the conductor. This only
holds if the conductor is kept at a constant temperature
Ohm’s law
For a conductor at a constant temperature, the current through it is proportional to the potential difference across it
Potential difference
The difference in electrical potential between two points in a circuit and
the work done that is required per coulomb to move a charge from the lower potential point to
the higher potential point. It is measured in Volts.
Potential divider
A combination of two or more resistors in series. These result in the
potential difference of the circuit being split into a specific ratio depending on the resistance
of the resistors. They can be used to get a specific output voltage from the circuit.
Power
Rate of energy transfer in a circuit. It can be calculated as the product of the current
and the potential difference between two points. Measured in Watts
Resistance
A measure of how difficult it is for current to flow in a circuit or component,
measured in Ohms and has symbol R
Resistivity
A measure of how difficult it is for charge to travel through a material, depending
on the material’s cross sectional area, length and resistance. It is measured in Ohm metres
and has symbol ⍴
Semiconductors
Materials that change their resistance depending on external conditions.
Terminal PD
The actual potential difference across the terminals of a
power source. It is the source’s EMF minus the voltage drop due to the source’s internal
resistance
Thermistor
When these components are heated up their resistance goes down. As
temperature increases resistance decreases.
Variable resitors
: A resistor that can have its resistance changed. Typically, these are
used with power supplies to change the voltage of a circuit without using a transformer
Voltmeter
A device used to measure the potential difference between two points on a
circuit, ideally it has infinite resistance so no current passes through it.
Resistance in parallel
(Equation)
1/Rtot = 1/R1+1/R2+1/R3…
adding more resistors decreases resistance
current and pd sharing in series and parallel
Series-current constant and pd divided across components
parallel- current shared across loops and total pd of one loop is emf
Potential divider equation
Vout=(R2/R1+r2) x Vin
output voltage is across R2
V1/V2=R1/R2
Resistivity practical
Plot resistance(V/I) over length of a wire. should make a straight line. Gradient makes R/L. Resistivity= R/L x A
