Electricity Flashcards
(42 cards)
What is electric current?
The rate of flow of electric charge, measured in amperes (A).
What is the difference between conventional current and electron flow?
Conventional current flows from positive to negative terminal; electron flow is opposite, from negative to positive terminal.
How is current measured in a circuit?
Using an ammeter connected in series with the component.
Define potential difference (p.d).
Electrical work done per unit charge between two points.
Measured in volts (V),
How does a cell create a potential difference?
By separating positive and negative charges at its terminals, causing electrons to flow when the circuit is closed.
How is potential difference measured?
Using a voltmeter connected in parallel across the component.
What is resistance?
The opposition to the flow of current in a component, measured in ohms (Ω).
Defined as R=V/I.
What effect does resistance have on current?
For a given potential difference, higher resistance means lower current; lower resistance means higher current.
What is Ohm’s law?
or a conductor at constant temperature, current is directly proportional to potential difference across it.
V∝I or V=IR.
How can you tell if a component obeys Ohm’s law from its I-V graph?
If the graph is a straight line through the origin, it obeys Ohm’s law.
Describe the I-V characteristics of a filament lamp.
The I-V graph is an ‘S’-shaped curve; resistance increases with temperature, causing current to increase slower than voltage.
Describe the I-V characteristics of a semiconductor diode.
Current flows only in forward bias (sharp increase in current), zero current in reverse bias.
How do you calculate current given charge and time?
𝐼=Δ𝑄/Δ𝑡
Why must a voltmeter be connected in parallel?
To measure the potential difference across the component without affecting the circuit current.
What is resistivity?
Resistivity is a material property that measures how much it opposes the flow of electric current.
How does the length of a wire affect its resistance?
Longer wire → greater resistance (because electrons collide more often).
How does the cross-sectional area of a wire affect its resistance?
Larger area (thicker wire) → lower resistance (more paths for electrons).
What is the unit of resistivity?
Ohm meter (Ω·m)
Why do metals have resistance?
Because free electrons collide with vibrating metal ions, transferring energy and resisting current flow.
How does temperature affect resistance in metals?
Increasing temperature → atoms vibrate more → more collisions → resistance increases.
What is the relationship between temperature and resistance in a thermistor?
Thermistor has negative temperature coefficient (NTC): as temperature increases, resistance de
Name three common applications of thermistors.
Ovens, fire alarms, digital thermometers.
Define superconductivity.
The property of zero electrical resistance below a critical temperature.
What is the critical temperature in superconductors?
The temperature below which a material becomes superconducting and resistance disappears.
