Electricity Flashcards
What is current?
The rate of flow of electrical charge flowing around a circuit
What is voltage?
The energy transferred/work done per unit of charge between two points in a circuit
What is resistance?
A measure of how much a material opposes the flow of current (it is the constant of proportionality between p.d. and current)
What is an Ohmic conductor?
A material that follows Ohm’s law meaning current and voltage are directly proportional to eachother, provided all other physical conditions remain constant (e.g. temperature) An example would be a metal wire at a constant temperature
Draw all of the circuit symbols and briefly explain what each one does
Look in booklet for answers
Draw and describe the I-V graphs of an Ohmic conductor, a filament lamp and a diode
Look in booklet for answers
Draw and describe the graphs for an LDR and a thermistor
Look in booklet for answers
How does the length of a wire affect its resistance?
A longer wire will have a higher resistance because the electrons have more material to travel through meaning the electrons collide with atoms in the wire more, which slows down the flow of current (electrons) leading to higher resistance
How does the cross-sectional area of a wire affect its resistance?
A larger cross-sectional area results in a lower resistance because there is more space for the electrons to flow through, which reduces the number of collisions of electrons with the atoms in the wire, allowing better flow of current (electrons) leading to lower resistance
How does the temperature of a wire affect its resistance?
A higher temperature results in an higher resistance because the atoms in the metal wire vibrate more, which increases the amount of collisions between the atoms and the free electrons, which slows down the flow of current (electrons) leading to higher resistance
How does the structure of the material of a metal wire affect its resistance?
If the spacing of the positive ions in the wire are closer together it will increase the amount that the free electrons collide with them, which slows down the flow of current (electrons) leading to higher resistance
What is resistivity?
A property of a material that describes how much that material opposes the flow of electrical current
What happens as a semiconductor is heated?
The positive ions vibrate more (like a normal metal) which increases collisions of electrons with the positive ions, which creates more resistance, however the heat energy allows more electrons to be released and become delocalised, meaning more current is flowing and so therefore less resistance
What are the uses of thermistors?
Anything that uses a temperature sensor e.g. thermometers, kettles, air conditioning, ovens, etc…
What is a superconductor?
A material that, when cooled below a certain critical temperature, has zero resistance (so can conduct very well)
What does the critical temperature of a superconductor depend on?
The type of material being used
What are some uses of superconducting materials?
- Power cables that transmit electricity without any power loss
- Really strong electromagnets that can create strong magnetic fields (useful for MRI scanners, particle accelerators and maglev trains)
- Electronic circuits that work really fast with minimal energy loss
What is the main problem with using superconducting materials?
It requires a lot of energy to cool materials to such low temperatures which can be expensive
How does current behave in series circuits?
The current is the same everywhere
How does voltage behave in series circuits?
The total voltage of the circuit is the sum of the voltages of the individual components in the circuit
How does the resistance behave in a series circuit?
The total resistance of the circuit is the sum of the resistances of the individual components in the circuit
How does current behave in parallel circuits?
The total current of the circuit is the sum of the currents of the individual components in the circuit
How does voltage behave in parallel circuits?
The voltage is the same everywhere
How does resistance behave in parallel circuits?
1/RT=1/R1+1/R2+1/R3+…
How does the voltage of cells in series add up?
You just add their voltages togehter
How does the voltage of cells in parallel add up?
They all have equal voltages
What is Kirchhoff’s first law?
That the total current entering a junction must equal the total current leaving that same junction
What is Kirchhoff’s second law?
The total e.m.f. around a series circuit is equal to the sum of the p.d.s across each component
What is a potential divider?
A circuit that uses 2 or more components (resistors, LDR’s, thermistors) to split the voltage supply into a desired smaller voltage, where the output voltage depends on the ratio of the resistances of the components
Look at the 3 different potential divider circuits in the booklet and re-answer the questions
Look in booklet for answer
What is a potentiometer?
A variable resistor used to create an adjustable potential divider, allowing you to smoothly change the voltage
What is e.m.f.?
The energy transferred from chemical energy to electrical energy per unit charge moved through the source
Define internal resistance
The resistance that is inside the source of e.m.f. (like a battery) and it reduces the total energy available to the external circuit
Define terminal p.d.
The voltage measured across the terminals of a power source when a current is flowing through a circuit (the p.d. across the external circuit when a current flows)
Define load resistance
The resistance of the external circuit (no including the internal resistance)
