Electricity Flashcards
What is electrical current?
The rate of flow of charge
What is potential difference?
Work done per unit charge
Sketch the current-voltage graphs for an ohmic conductor, semiconductor diode and filament lamp.
-
What is Ohm’s law?
Electric current is directly proportional to potential difference, under constant physical conditions
How does the resistance of a metal conductor vary with temperature?
The resistance of a conductor increases with temperature. This is because as the temperature increases the atomic lattice of the conductor has more energy so begins to vibrate more. This means it is more likely for any electrons travelling within the conductor to interact with atoms thus increasing its resistance
Describe how a NTC thermistor works
Resistance decreases as temperature increases. This is because more charge carriers are released at higher temperatures, increasing the currrent, and therefore decreasing the ratio of current to p.d. in the circuit
Applications of thermistors
Temperature sensors, which trigger an event to occur once the temperature reaches a certain value eg turning the heating on
Also can be use to produce resistance temperature graphs
What is superconductivity?
A property of certain materials which
have zero resistivity at and below a critical temperature
which depends on the material.
Applications of superconductivity?
No resistance means an infinite current can be passed through, creating a large magnetic field which is used for maglev trains
Used in power cables, as the power loss due to heating is zero due to no resistance
What is conserved in d.c circuits
Charge and energy, meaning that the current flowing out of any junction is the same as the current flowing in, and the sum of all voltages in each circuit loop is equal to the battery voltage
What is a potential divider?
A combination of resistors in series, which results in the p.d. in the circuit being split into a specific ratio. Variable resistors can be used, to allow the p.d. to vary
Potential divider equation
vout= vinX r1/r1+r2
Define terminal pd.
The potential difference across the terminals of a cell
Define EMF
The energy transferred from chemical energy to electrical energy by a cell per coulomb of charge that passes through it
Define internal resistance
The resistance of the materials in the battery, it is the loss of voltage per unit current
