Resitance Flashcards
How does resistance affect current in a circuit
As the total resistance of a circuit increases the current flowing through the circuit decreases
How can current in a circuit be varied
Using a variable resistor
Equation linking current and resistance
Current=P.D/Resistance
How is the total resistance affected by two resistors in series
The total resistance increases it is equal to the sum of the two resistors
How is total resistance affected by two resistors in parallel
The total resistance decreases it is less than the resistance of the resistor with the lowest resistance
What is an ohmic conductor state the condition required
A conductor for which is current and potential difference are directly proportional
Resistance remains constant as current changes
Temperature must be constant
List 4 components for which resistance is not constant as current changes
Filament lamps
Diodes
Thermistor
LDR
What happens to the resistance of a filament lamp as the temperature increases?Why?
Resistance increases
Metal ions have more kinetic energy, so vibrate more , colliding more frequently with electrons as they flow through the metal
This creates more resistance to current flow
What is different about current flow through a diode
The current only flows in one direction
Resistance is very high in the other direction preventing current flow
What happens to the resistance of a thermistor as temperature increases
The thermistors resistance decreases
Where can a thermistor be used
In a thermostat to turn a heater on below a certain temperature
In a freezer to turn on a cooler when the temperature becomes too high
What happens to the resistance of an LDR as light intensity decreases
The LDRs resistance increases
Application for an LDR
Street lamps or night lights
When light levels drop resistance increases and the light gains sufficient current to turn on
How do diodes work
A diode allows current to flow in one direction. If current is flowing the right way , the resistance is large for small voltages but then at higher voltages becomes very small
