Electricity 1 Flashcards
Define current
the rate of flow of charge
Which way does conventional current flow?
positive to negative
How should an ammeter be connected?
in series
What is one coulomb?
the charge that flows past a point in one second when there is a current of one amp
What is Kirchhoff’s first law?
the total current that enters a junction is equal to the total current that leaves a junction
Define potential difference
the work done when one coulomb of charge moves between two points
Define electromotive force (EMF)
the amount of electrical energy a power supply transfers to each coulomb of charge
What is the relationship between current at each point in a series circuit?
current is the same at all points
What is Kirchhoff’s second law?
the total EMF around a series circuit is equal to the sum of the potential difference across each component
How should a voltmeter be connected?
in parallel
Define power
the rate of doing work
Define resistance
the rate of potential difference across a component to the current through the component
What is ohm’s law?
for an ohmic conductor at a constant temperature, the current is directly proportional to the potential difference across it
What is the I-V graph for an ohmic conductor?
directly proportional graph
What is the I-V graph for a diode?
I is very small (basically zero) up to the threshold voltage of 0.6V where I increases almost vertically
Give an example of an ohmic conductor
a resistor
What is the threshold frequency for a diode?
0.6V
What is the I-V graph for a filament lamp
- I and V are initially directly proportional
- After, for the same increase in V, the increase in I becomes progressively smaller
Explain the I-V graph of a filament lamp
1) as voltage increases, current increases
2) As current increases, temperature increases and thus positive ions vibrate more
3) Therefore electrons collide with positive ions more frequently
4) Therefore resistance increases
How much resistance can ammeter be assumed to have?
0 resistance
How much resistance can voltmeters be assumed to have?
infinite resistance
What happens to the resistance of a thermistor as its temperature increase?
As temperature increases, resistance decreases
Why is it that as the temperature of a thermistor increases, its resistance decreases?
1) increasing the temperature of the thermistor causes electrons to be emitted from atoms
2) thus the number of charge carriers increases and so the current increases
3) causing resistance to decrease
