Electricity: Basics Flashcards
What is the definition of an electric current?
An electric current is the rate of flow of charge past a point in a circuit.
What is current measured in and what is it’s state symbol?
Current is measured in Ampere’s (A) and it’s symbol is I.
What is charge measured in and what is it’s state symbol?
Charge is measured in Coulombs (C) and it’s symbol is Q
What charge does one electron carry?
1.6 x 10⁻¹⁹ C
What charge does one proton carry?
1.6 x 10⁻¹⁹ C
What is charge?
Charge is a property carried by some particles.
What’s an ammeter?
An ammeter is a device used to measure current in a circuit.
How do we calculate charge?
Q = I x T
What is the definition of potential difference?
The work done per unit charge
How do we connect ammeters into a circuit?
In series.
How do we connect voltmeters into a circuit?
In parallel.
How do we calculate voltage? (without resistance)
V = W / Q
What is the definition of resistance?
R = V / I
What is resistance?
Opposition to the flow of charge.
What is Ohm’s Law?
For a metallic conductor at a constant temperature, the current is directly proportional to the potential difference? Alternatively, this can be shown as V = I x R
What does the graph of an Ohmic Resistor on an I - V graph look like?
A straight line that goes through the origin where the gradient remains constant.
What does the graph of a filament lamp on an I - V graph look like?
A straight line that goes through the origin until it starts to curve at both ends and flattens out.
What does the graph of a diode on an I - V graph look like?
A flat line that goes through the origin and goes upwards sharply once it has reached the threshold.
Why does the graph of an Ohmic Resistor look the way it does?
The resistance is constant so the gradient doesn’t change.
Why does the graph of a filament lamp look the way it does?
As the current increases, the filament heats up causing vibrations in the metal ions. This increases the chance that electrons will hit the metal ions which increases resistance lowering the gradient on the graph.
Why does the graph of a diode look the way it does?
Below a threshold P.D. the resistance is infinite so no current flows. Above the threshold P.D. there is very little resistance so the gradient is very steep.
What is a conductor that follows Ohm’s law called.
An Ohmic Conductor
What is a conductor that doesn’t follows Ohm’s law called.
A Non Ohmic Conductor
