Electricity Flashcards
What is Conventional Current Flow?
Flow from positive to negative in a circuit
How is current measured?
In Amperes, symbol I
What is the function of a Diode?
Allows current to flow in one direction only
What is the typical threshold voltage for diodes?
Approximately 0.7 V
Define Electromotive Force (EMF)
The energy per unit charge transferred electrically by a source, measured in V.
What is Electron Flow?
Flow of electrons from negative to positive in a circuit
What is Internal Resistance?
Resistance within a power source that dissipates energy
State Kirchoff’s First Law
Total current entering a junction equals total current leaving a junction
State Kirchoff’s Second Law
Sum of EMF in any loop equals sum of potential differences of each component
What are Light Dependent Resistors (LDR)?
Resistance decreases as light intensity increases
What defines an Ohmic Conductor?
Follows Ohm’s law, where current is directly proportional to potential difference at constant temperature.
What is Ohm’s Law?
Electric current is proportional to potential difference at constant temperature
What is a Parallel Connection?
Components on separate loops with the same potential difference
Define Potential Difference
The transfer of electrical energy per unit charge to other form of energy between two points in a circuit.
What is a Potential Divider?
Combination of resistors in series that splits potential difference
How is Power calculated in a circuit?
Product of current and potential difference, measured in Watts
What is Resistance?
Measure of the opposition to flow of current, measured in Ohms, symbol R and is found by the ratio of V/I.
Define Resistivity
Difficulty for charge to travel through a material, measured in Ohm metres, symbol ⍴
What are Semiconductors?
Materials that change resistance based on external conditions such at temperature and light levels.
What is a Series Connection?
Components on the same loop with potential difference shared between them
What is Terminal Potential Difference?
Actual potential difference across power source terminals, EMF minus lost volts
What is a Thermistor?
Resistance decreases as temperature increases
What are Variable Resistors?
Resistors with adjustable resistance, used to change circuit voltage
What is the purpose of a Voltmeter?
Measures potential difference between two points, ideally has infinite resistance
Define current
Rate of flow of charge
Define a charge carrier, n
An electron detached form its atom or an ion in a conducting material that is free to flow in order to create a current
What is the difference between thermal energy and heating in terms of a hot filament?
The hot filament is hot and has a thermal energy (store), it transfers energy to its surrounding (HOT to COLD) via heating.
What is a volt?
Where 1 joule of energy is transferred when 1 C of charge passes between two points in a circuit.
Define 1 ohm
when a potential difference of 1 V across a component produces a current of 1A through it.
How do you calculate the power dissipated in a wire?
It is best to use
Define positive temperature coefficient
when a materials resistivity increases when temperature increases. (like a wire)
Define negative temperature coefficient
when a materials resistivity decreases when temperature increases. (like a thermistor)
As a rule of thumb….The total resistance of resistors in parallel…
Is always smaller than the smallest resistor.
What is the difference between a rheostat and a potentiometer.
A rheostat in series control current, a potentiometer in parallel controls voltage.
What is the breakdown voltage of a diode.
the minimum reverse voltage at which a significant current begins to flow through the diode in the opposite direction
How can the EMF of a cell be measured?
Connect a very high resistance voltmeter (multimeter voltmeter) across it so that no current is drawn from the battery - no lost volts
