[custom] 4.2 test remade Flashcards
Define potential difference.
The energy transferred from electrical energy to other forms, per unit charge by the charges passing through the component. It is measured across a component.
Define 1 Volt
The PD between two points when 1 Joule of work is done to move a charge of 1 Coulomb.
What equation is used to find Potential Difference and EMF?
V = W/Q E = W/Q
Potential difference is a measure of what?
The work done by charge carriers, which lose energy as they pass through the components in a circuit.
Define electromotive force.
The energy transferred from chemical energy into electrical energy per unit charge, by charges passing through a supply.
What is EMF used as a measure for?
Used to measure the work done to charge carriers, when they gain energy as they pass through a cell or a power supply.
Explain what resistance is?
A measure of how difficult it is for current to flow through a component.
How do we determine the resistance of a component?
What is the resistance equal to on the graph of results?
Setup a circuit with a variable power supply, an ammeter in series with the component, and a voltmeter in parallel with the component.
By varying the power supply, we can vary the potential difference across the component, and record the PD and current to calculate the resistance.
The resistance is equal to 1 over the gradient of the IV graph.
State Ohm’s law
For a metallic conductor kept at a constant temperature, the current in the wire is directly proportional to the potential difference across it.
Where Ohm’s law is true, components are considered ____, and their IV characteristics graph will have a _____ ______ gradient.
Where Ohm’s law is true, components are considered OHMIC, and their IV characteristics graph will have a CONSTANT LINEAR gradient.
What happens when the current across a non ohmic component increases?
The metal ions are heated, gaining kinetic energy and vibrate more around their fixed points in the metallic lattice.
This increases the frequency of collisions with electrons, so more work is done on the charge carriers, increasing the resistance.
How are fixed resistors designed?
Designed so that their resistance is always constant, despite environmental changes.
Do fixed resistors follow Ohm’s law? Why?
They follow Ohm’s law. This is because the PD is proportional to current.
Judging by its IV characteristics, are filament lamps ohmic or non-ohmic?
They show that the component is non-ohmic.
but as the magnitude of the current increases,
What are diodes?
Components made from semiconductors, which allow current to flow only in one direction.
Are diodes Ohmic or Non-Ohmic?
Non Ohmic.
What occurs when a diode is reverse biased?
It does not conduct at all, and the resistance across it is infinite.
What does it mean if a semi-conductor has a negative temp coefficient?
Where would these NTC semi conductors be useful?
As the temp of the material increases, the resistance of the material decreases.
They are useful in temp sensing circuits such as thermometers and thermostats.
Are thermistors ohmic or non ohmic?
Why?
Non ohmic
It is made of an NTC semi conductor material.
What are thermistors made of?
What happens as the current through a thermistor increases?
It is made of an NTC semi conductor material.
As the current, hence the temperature, through the thermistor increases, the resistance decreases.
What are LDRs?
What do they do?
LDRs are small, non-ohmic components made from semi conductors.
When the light intensity incident on the resistor increases, the resistance of the LDR decreases.
What is resistivity?
A measure of how difficult it is for charge to travel through a material.
What is resistance proportional to?
Proportional to: Length.
Proportional to: 1 / Area
This means it is inversely proportional to area.
The resistivity, p, of a material is a ______ property of the material.
It is the same for any ___ of a given material at a set ____.
The resistivity, ρ, of a material is a PHYSICAL property of the material.
It is the same for any SHAPE of a given material at a set TEMPERATURE.
