DC Electricity Flashcards
Current
The rate of flow of charge at a point in a circuit
What is used instead of an ammeter for very small currents?
A galvanometer / galvo
What is the resistance of an ideal ammeter?
0 ohms
Direction of flow of current
Positive to negative
Direction of flow of electrons
Negative to positive
Potential difference between two points
The energy converted when a unit charge flows between the points
What is the resistance of an ideal voltmeter?
Infinite resistance
Resistance of a devise
The ratio of the potential difference across its ends to the current flowing through it
What is resistance a measure of?
How difficult it is for current to flow
Ohm’s law
Provided the temperature and other physical factors remain constant, the current through a conductor is directly proportional to the p.d across it.
Power
The rate at which energy is converted
A kilowatt-hour
The energy supplied by 1 kilowatt of power in 1 hour
Kirchoff’s 1st law
At a junction, the total current entering the junction is equal to the total current leaving the junction
Explanation for the shape of a V-I graph
- Obays Ohm’s law at low PD and I
- As PD increases, I increases
- As I increases, more power is dissipated
- As more power is dissipated, the temp increases
- As temp increases, resistance increases
- As resistance increases, there is a smaller increase in I for the same increase in PD
Why does resistance increase at high temperatures?
The metal ions vibrate more vigorously, making it more difficult for electrons to flow through a wire
