Electricity Flashcards
What is current ?
Rate of flow of charge in coulombs per second
What is the formula for charge current and time ?
Q = IT
What is the difference between electron flow and conventional current ?
conventional current is what is normally shown in Q’s where current flows away from positive and towards negative, electron flow is the opposite.
What is Ohm’s Law ?
The current flowing through a metallic conductor is directly proportional to the potential difference applied across it at a constant temperature.
V=IR
What is the charge of one electron ?
-1.6x10^-19
What is the definition of potential difference ?
PD between two points is the amount of energy transferred when one coulomb of charge passes through
What is the formula for work done ?
W = QV
What is the formula for power ?
W = PT
P = IV
What does a current voltage graph look like for a diode ?
current only allowed through one direction and is flat then increases
What does a current voltage graph look like for a fixed resistor ?
Linear through origin
What does a current voltage graph look like for a filament lamp ?
Linear through origin but then plateaus
WHat does it mean when a component is ohmic ?
Ohms law applies.
What is a potentiometer circuit ?
When a component is in parallel with a variable resistor which can be moved to change current through the component can be seen as component in parallel with a resistor then series with another.
What are the rules for a parallel circuit ?
Current is split between branches and PD is same everywhere
WHat are the rules of a series circuit ?
Current is the same everywhere and PD is split amongst components
What is Kirchoffs first law ?
At any junction in a circuit the sum of the current flowing into the junction is equal to the sum of the current flowing away from it
What is Kirchoffs second law ?
In any complete loop of a circuit the sum of PD is equal to PD of the scource
What is the formula for resistors in parallel ?
(1/r1 +1/r2 …)^-1
What is the formula for resistors in series ?
r1 + r2 ….
What is the relationship between resistors in a series circuit ?
And how would you work out PD across each resistor ?
resistor with largest resistance will have the largest PD vice versa. This is because current is equal everywhere but resistance is different so PD across each resistor is different
V(resistor) = R(resistor)/R(total) x V(total)
What is a NTC thermistor ?
As temp increases resistance decreases
What is a PTC resistor ?
As temp increases resistance increases
What is a LDR ?
As light intensity increases resistance decreases
What is the resistivity of a metal ?
How resistive the metal is in ohms per metre
What is the formula for resistivity ?
R = ρ x L/A
How do you work out the voltage across branches ?
On each side of voltmeter do one value take away the other
(see p29 electricity booklet for clarity)
What is a superconductor and what are its uses ?
a type of material that conducts electricity with zero energy loss or resistance when cooled to its critical temperature
maglev trains
What is the emf of a cell ?
Work done per unit charge on the whole circuit by the power source
What is the TPD of a cell ?
Voltage across terminals when current is passing through
WHy is TPD lower than the emf ?
Battery has internal resistance which can be shown as a resistor in series with the cell. This “resistor” uses x volts when current is flowing through working against the battery therefore it is lower
