Topic 2- Current, Potential difference, and resistance Flashcards
What is electric current
The flow of electrical charge
State the equation linking charge, current and time.
Charge (Q) = Current (I) x Time (t)
charge= coulombs current= amperes time=seconds
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 two factors does the current in a circuit depend on?
potential difference (V)
resistance (R)
What equation should be used to calculate potential difference if current and resistance are known?
Potential difference (V) = current (I) x resistance (R)
p.d = V current= A resistance= ohms
What is an ohmic conductor? state the conditions required
A conductor for which current and p.d are directly proportional
-resistance remains constant as current changes
-temperature must be constant
List four components for which resistance is not constant as current changes
Lamps, Diodes, Thermistors, Light dependant resistors (LDRs)
What happens to the resistance of a filament lamp as the temperature increases? why?
resistance increases
Ions in metal have more energy, so vibrate more, causing more collisions with electrons as the 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 other direction preventing current flow
State what happens to the resistance of a thermistor as temperature increases
The thermistor’s resistance decreases
Give two examples of when a thermistor may be used
in a thermostat to turn a heater on below certain temperature
in a freezer to turn on cooler when the temperature becomes too high
State what happens to the resistance of a LDR as light intensity decreases
The LDRs resistance increases
Give an application for a LDR
Street lights often use LDRs
When light levels become too low, the light gains sufficient current to turn on