Electricity Flashcards
Which way do electrons flow in a circuit
Positive end to negative end
State what is Ohm’s Law
Current flowing through a metallic conductor is directly proportional to the potential difference across it at a constant temperature
Define potential difference (the volt)
Potential difference is amount of energy transferred when one coulomb of charge is moved between the two points
Define power and state it’s units
Rate of doing work / rate at which energy is transferred
Joules per second = watts
Draw a current voltage graph for a fixed resistor, a diode and a bulb
Differences between a variable resistance and a potential divider
Why does resistance increase for a filament bulb
Filament is made of metal which is made up of metal ions bonded together in a lattice
Electrons have to pass through gap in lattice
As current increases, temperature of filament increases, more number of collapses per second
Causing lattice ions to vibrate more, making it harder for electrons to pass through collision
Why does resistance decrease for a diode
Diode is a semi conductor
Electrons in a semi conductor are weakly bound and require some energy to become free from semi conductor
At a threshold voltage, electrons gain enough energy to become free, so current increases
As vintage increases current increases
Define resistance
Ratio of voltage applied to a current through a material
Name one practical use for a semi-conductor diode
Ensuring current only flows through one way
Rules for series circuit
Rules for parallel circuit
What is Kirchoffs first law
At any junction in a circuit sum of current flowing into the junction of equal to the sum flowing away from it
What is kirchoffs second law
In any complete loop of a circuit sum of p.d’s equals the source p.d
Calculations for resistors in series
Calculation for resistors in parallel
State the rules applied here
What happens to p.d across resistors when resistors in series
P.d will be equally divided across them as largest resistance will get largest p.d
What is meant by NTC (negative temperature coefficient)
State difference of PTC
- what should you assume a thermistor is
As temperature increases, resistance of thermistor decrease
- unless told otherwise, assume it is a NTC
Rule for LDR, light dependent resistor
As light intensity increases, resistance of LDR decreases
Even though 10 ohm resistor and 50 ohm resistor have different voltage and resistance, they must have same current as they are in series so simply do 12/60