Electricity ⚡︎ Flashcards
If a bulb in series melts why does series bulb 2 get brighter and parallel bulb get dimmer ?
Circuit resistance increases so the current decreases meaning greater share of voltage across series bulb 2
Energy equation
E = Vit
Why do bulbs have same light intensity but different power
Power is lost as thermal energy and more energy can be wasted in certain lamps
Ohmic conductor
I is directly proportional to V
Electricity required practical
Hhh
Principal property of a superconductor
Zero resistivity
Critical temperature
Material becomes superconducting at crit temperature
Use of a superconductor
Maglev trains
Magnets
Bullet trains
Particle accelerators
Conditions of superconductivity
Zero resistance
Resistance decreases with temp
Superconducts when crit temp is reached
Filament current alternation
Resistance of filament increases
As temp of filament increases
Explain change if a lamp is connected to a similar lamp in series
Voltage of supply now shared by lamps
Current is reduced
Explain the change if a lamp is connected to a similar lamp in parallel
Current through the lamp is unchanged
Both directly connected to the supply
Why is a filament lamp more likely to fail to switch on
Resistance of lamps lowered when switched on
Hence initial current will be larger
Sudden rapid change in temp
Electric current
Rate of flow of charge
I = Q/T
Potential difference
Work done per unit charge
V = W / Q
Resistance
Measure of how difficult it is for charge carriers to pass through a component
R = V / I
Diode
HIGH resistance
Only small amount of current can flow
Filament
Wire that heats up as current increases
Low current = no heat = Ohm’s law obeyed
If current increases then resistance increases
Resistivity
How easily a material conducts electricity
p = RA/L
Why if temp increases does the resistance increase
Atoms will gain kinetic energy and move more causing charge carriers to collide with the atoms more frequently so they slow down
Therefore current decreases and resistance increases (R = V / I)
Thermistor
Temp increase = resistance decrease
Increase of temp causes electrons to be emitted from atoms
Therefore number of charge carriers increases and so resistance decreases
Application of a thermistor
Temperature sensor
Series equation
RT= R1 + R2 + R3…
Parallel equation
1/RT = 1/R1 + 1/R2 + 1/R3 + …
