Electricty Flashcards
(10 cards)
Explain the IV curve of a filament lamp
Mention gradient relationship to resistance
Higher gradient = less resistance = 1/R
As current rises filament heats and resistance grows - more temp means increased movement of atoms means more electron collisions per second (RATE OF COLLISIONS)
What is JC-2S equivalent to?
Ohms
What is the definition of EMF
Pd across terminals in an open circuit OR Electrical E transfered p unit charge OR work done by cell p unit charge
How do you find how V across thermistor changes with temperature?
Voltmeter across thermistor Vary temp with a water bath Make sure to stir it and use a thermometer or ice to cool it down. plot a calibration curve of V against T Use a resistor as a control,
Why is V less than EMF when a switch is closed
Current flows therefore there is an internal resistance in the power supply and lost volts
Superconductivity definition
Material has zero resistance
Resistivity drops when cooler becomes superconducting below critical temperature
How to find IV of a semi conductor diode
connect circuit up measure current and voltage vary resistance obtain a range of results reverse connections and repeat plot a graph 0.6 v critical voltage disconnect between readings
Explain why a thermistor is better equipped to deal with a surge in current
Thermistor as current rises and temp rises resistance falls
Resistor is the opposite
less wasted piwrt
Why does more external resistance mean a more efficient circuit?
More external resistance = less current
Less current = less lost volts
EMF=0.7 V
Internal R = 0.78 Ohms per cell
How to create emf 14v
Internal R 3.9 Ohms
Need 20 cells in series to achieve 14V
IR: 15.6 Ohms internal res
Need cells in parallel to lower IR
Four parallel sets of 20 cells divides IR by four achieving 3.9
