current, pd and resistance Flashcards
current, pd and resistance
what is the flow of electric current?
the flow of electrical charge
state the equation for charge
Q = IT
charge(coulombs) = current(amperes) x Time(seconds)
what is the value of current at any point in a single closed loop
current is the same at all points in a closed loop
what 2 factors does the current in a circuit depend on
- potential difference
- resistance
what is the equation linking current, voltage and resistance
V = IR
potential difference = current x resistance
what is an ohmic conductor
- current and potential difference are directly proportional
- resistance remains constant as the current changes
- temperature must be constant
components where resistance is not constant as the current changes
- lamps
- diodes
- thermistors
- ldrs
what happens to resistance in a filament lamp as the temperature increases
- resistance increases
- ions in metal have more energy, colliding more, causing more collisions with electrons as they flow through the metal
- creating greater resistance to current flow
what happens as current flows through a diode
- current only flows in 1 direction
- resistance is very high in the other direction, preventing current flow
what happens to the resistance of a thermistor as temperature increases
thermistors resistance decreases
2 examples when a thermistor may be used
- in a thermistor to turn a heater on below a certain temp
- in a freezer to turn on a cooler when the temp becomes too high
thermistors resistance depends on the temp
how are they related
as the temperature increases, the resistance decreases
what happens to an ldr as the light intensity decreases
the ldrs resistance increases
give an application for an ldr
- street light
- when light levels become too low, the light gains sufficient current to turn on
