Circuits Flashcards
Ohm’s Law?
The current passing through a conductor is directly proportional to the potential difference across the conductor as long as temperature is kept constant.
Potential Difference?
The work done per unit positive charge, V= W/Q
Current?
The rate of flow of charge, I = Q/t
Resistance?
A material’s opposition to the flow of electric current.
Emf?
Electromotive Force. The total energy supplied per coulomb of charge by the cell.
One Ohm?
Unit describing the resistance a conductor has if a potential difference of 1V applied across it causes a current of 1A to flow through it. Ω = V.A¯¹
Equivalent Resistance?
The resistance of the single resistor which can replace two or more resistors in a circuit without changing the total current through that section of the circuit.
Properties of Series Circuits?
Current flows along one path only.
The sum of voltages across individual components is equal to the voltage across the battery.
Equivalent resistance is made up of the sum of all the resistors aligned in series.
Properties of Parallel Circuits?
Current divides, sum equals total current flowing in the circuit.
Voltage across individual components are all equal to the potential difference across the battery.
Equivalent resistance is smaller than that of the smallest resistor in the circuit.
Ohmic Conductors?
Obey Ohm’s Law over a wide range of conditions. To elaborate, under their normal operating conditions, the change in resistance is small enough to ignore. Examples include: constantan, manganin, nichrome, carbon resistors, generally most metals.
Ohmic behaviour?
Shows a linear relationship between the voltage across a conductor and the current flowing through it, should apply to metals if T is kept constant. Therefore, resistance can be calculated from the gradient of the slope.
Non-Ohmic Conductors? Give two examples.
Don’t obey Ohm’s Law. Examples include: tungsten, silicon, germanium and diodes.
Non-Ohmic behaviour?
Shows a non-linear relationship between the voltage across a conductor and the current flowing through it. Therefore, we cannot use the gradient to find the resistance.
Properties of Metallic Non-Ohmic Conductor?
At higher temperature, metals have higher resistance. This is because when temperature increases, the + ions vibrate more and cause more restriction to the flow of electrons. The V vs I graph for a resistor behaving in a non-ohmic way is concave shaped.
Properties of Semi-Conductors?
At higher temperature, semi-conductors have lower resistance. This is because the valence electrons get energized and become free to move meaning less restriction to the flow of electrons. The V vs I graph for these are convex shaped.
