Module 4 Flashcards
Define electric current
The rate of flow of charge
What is the coulomb?
The unit for charge
What is the charge on an electron, in terms of elementary charge?
-e
What is the charge on a proton in terms of elementary charge?
+e
What is current?
The movement of electrons in metals and movement of ions in electrolytes
What is convential current, and how is this different from electron flow?
Convential current is the flow of charge from positive to negative. Electron flow, which is what actually happens, is electrons moving from negative to positive, so has the opposite direction
Define Kirchhoff’s first law
For any point in an electrical circuit, the sum of the currents into that point is equal to the sum of currents out of that point
Define number density of a material
Number of free electrons per cubic metre of material
Describe how materials can be classified as conductors, semiconductors and insulators
Their number density is used, where a high number density suggests that it is a conductor, and a very low number density suggests an insulator
Define mean drift velocity
The average velocity of electrons as they move through a wire
Define potential difference
The measure of the transfer of energy by charge carriers.
Define the volt
The potential difference across a component when 1 J of energy is transferred per unit charge passing through the component
Define electromotive force
The energy transfered from chemical to electrical energy per unit charge
Give the difference between e.m.f. and p.d.
- Potential difference is used to describe when work is done by the charge carries.
- Electromotive force is used to describe when work is done on the charge carriers
Define resistance
A property of a component calculated by dividing the potential difference across it by the current in it.
Define the ohm
The resistacne of a component when a p.d. of 1 V is produced per ampere of current
Define ohm’s law
For a metallic conductor kept at a constant temperature, the current in the wire is directly proportional to the p.d. across its end
Describe the I-V characteristics of a resistor
The graph of I against V gives a straight line throught the origin. The steeper the gradient, the lower the resistance
Describe the I-V characteristics of a filament lamp
- The p.d. across the filament lamp is not directly proportional to the current through the resistor
- The resistance of the filament lamp is not constant
- The graph of I against V gives a ‘s’ shape through the origin
Define ohmic conductor
A conductor which obeys Ohm’s law, e.g. a resistor
Define non-ohmic component
A component which does not obey Ohm’s law, e.g. a filament lamp
Describe the I-V characteristics of a diode/LED
- When the voltage is negative, there is no current
- As the voltage is increased, the resistance gradually starts to drop when the threshold p.d. of the specific diode is reached.
- Above this voltage, the resistance drops sharply for every small increase in the p.d., so the diode has very little resistance
