P2 topic 2 Flashcards
when is the heat in resistors made of use?
in electric cheaters and the heating element of an electric kettle
what can cause fires?
excessive heat produced in electrical devices can cause fires if there are no safety features- an overloaded mains socket is a potential fire hazard
what is an example of safety feature to prevent fires in an electrical device?
cooling fan in a laptop
what can be used to calculate how much it would cost to use a device?
electrical power
what can be used to calculate how much electrical energy a device will transfer?
electrical energy
electrical power
the rate of energy transfer
what happens when current flows?
electrons travel through the lattice of the metal
what causes heating in a circuit?
electric current- the heating is the result of collisions between electrons and the ions in the lattice
heat energy
collisions cause increased vibrations (around fixed positions) of the ions
what does LDR stand for
light dependent resistor
LDR
a special type of resistor made from a semiconductor material
what happens the the resistance of a LDR as intensity of light incident on it increases?
the resistance decreases as light intensity increases- more light means less resistance- circuits with LDRs can be used to detect changes in light intensity
thermistor
special type of resistor- its resistance depends on temperature- a sensor in a electric circuit that detects temperature changes
what happens to the resistance of a thermistor as temperature increases?
the resistance of a thermistor decreases as its temperature increases- greater temperature means less resistance
where are LDRs used?
simple light-meters, light-sensitive circuits in burglar alarms and circuits for automatically controlling how much light enters a camera
where are thermistors used?
simple electrical thermometer, circuit to switch off fan inside laptop when it overheats, central-heating controller that senses temperature
why are metals not used for thermistors?
increasing the temperature of a metal does not significantly change the number of conduction electrons- in semiconductors and metal oxides, more temp frees up more electrons from atoms and causes resistance to decrease
what are LDRs made from?
semiconductors that are responsive to light- as the intensity of light falling on a LDR increases, this frees up more electrons from the atoms and this causes the resistance to decrease
what causes a resistor to heat up?
the current in the resistor
what can be used to determine the resistance in a wire?
the potential difference across the wire and the current in the wire
what is the relationship between the resistance of a wire and it’s length?
the resistance of the wire is directly proportional to its length- the resistance doubles when the the length is doubled
rheostat
variable resistor
how can the resistance of a rheostat be changed?
manually
what happens when a resistor is set to its maximum value?
the current in the circuit is low
