1.9 - Current-potential difference relationships
● ***Rheostat: variable resistor; can be used to control current in a circuit/give a
continuously variable PD (known as a potential divider in this case)
I-V characteristics for different materials
● (gradient = 1/R)
Metallic conductors Filament lamp Semiconductor diode
(Ohmic)
Thermistor Light-dependent resistor (LDR)
Ohm’s law and resistance
● I ∝ V , given that temperature remains constant (so resistivity\resistance remain
constant)
● ***V ( potential difference [V ])=I ( current [ A]) × R(resistance[Ω])
V V
● ∵ I ∝ V , V =IR , ∴ R= (where the ratio is constant)
I I
● For filament lamps - as temperature increases, resistance increases
1
● ***Rheostat: variable resistor; can be used to control current in a circuit/give a
continuously variable PD (known as a potential divider in this case)
I-V characteristics for different materials
● (gradient = 1/R)
Metallic conductors Filament lamp Semiconductor diode
(Ohmic)
Thermistor Light-dependent resistor (LDR)
Ohm’s law and resistance
● I ∝ V , given that temperature remains constant (so resistivity\resistance remain
constant)
● ***V ( potential difference [V ])=I ( current [ A]) × R(resistance[Ω])
V V
● ∵ I ∝ V , V =IR , ∴ R= (where the ratio is constant)
I I
● For filament lamps - as temperature increases, resistance increases
1
