P4: Electricity Flashcards
What is electric current?
The flow of electrical charge
State the equation linking charge, current and time?
Q = I t
What can be said about 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 equation should be used to calculate potential difference if current and resistance are known?
V = I R
What is an ‘Ohmic conductor’?
A conductor for which current and potential difference are directly proportional
Resistance remains constnat as current changes
Temperature must be constant
List 4 components for which resistance is not constant as current changes?
Lamps
Diodes
Thermistors
Light Dependent Resistors
What happens to the resistance of a filament lamp as the temperature increases?
Resistance increases
Ions in metal have more energy, so vibrate more, causing more collisions with electros as they flow through the metal, creating greater 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
State what happens to the resistance of a thermistor as temperature increases?
The thremistor’s resistance decreases
Give 2 examples of when a thermistor may be used?
In a thermostat to turn a heater on below a certain temperature
In a freezer to tuen on a cooler when the temperature becomes too high
State what happens to the resistance of a LDR as light intensity decreases?
The LDR’s resistance increases
Give an application for a LDR?
Street lights often use LDRs
When light travels become too low, the light gains sufficient current to turn on
