Electricity Flashcards
what is an electric current?
flow of charge
what is charge measured in?
coulombs
what is the direction of electron flow?
negative to positive`
what is a conventional current?
positive to negative
what is p.d.?
gain/loss of energy per coulomb of charge moving through an object
when charges move through battery…
they gain potential energy
when charges move through bulb…
they give up potential energy
what is current?
number of coulombs passing through fixed point per second
how does a bulb work?
converts electrical energy into light
how does a variable resistor work?
converts electrical energy into heat
rule of p.d.
p.d. is always conserved
p.d. in series circuits
- p.d. shared between compononents
- some may be lost to wire
p.d. in parallel circuits
- p.d. same for battery and bulbs
rule of current
current is conserved - total current flowing in is equal to total current flowing out
current in series circuits
same everywhere in circuit
current in parallel circuits
shared between bulbs
what is resistance?
measure of how hard it is for current to flow through a component
how is resistance related to length?
directly proportional (longer wire - higher resistance)
how is resistance related to area?
indirectly proportional
thinner wire - higher resistance
how is a resistor designed?
to have a constant resistance (obeys ohm’s law)
characteristics of voltage-current graph of resistor
linear: current is directly proportional to resistance
high resistance - low currrent - (shallow)
low resistance - high current - (steep)
characteristics of voltage-current graph of bulb
- gradient becomes less steep as current increases
because resistance increases as temperature increases (in a metal) - graph curves when bulb reaches working current/temp
how is a diode designed?
- to make sure current only flows one way (low voltage used to prevent overheating)
- turns A.C. into D.C
characteristics of voltage-current graph of diode
when voltage is negative, no current is let through (reverse biased)
when voltage is above 0.7 V, resistance drops so current flows through - steep gradient (forward biased)
what happens to the resistance when light input increases? (in a LDR)
decreases
why does resistance decrease when light input increases? (in a LDR)
electrons gain energy
move more easily
what happens to the resistance when heat increases? (in a thermistor)
decreases
why does resistance decrease when heat increases? (in a thermistor) when heat increases? (in a thermistor)
electrons gain energy
move more easily
uses of LDR
- light sensors
- burglar alarms
- car headlamps
- streetlights
- cameras
uses of thermistor
- fridges
- ovens
