2.1 Current, Potential Difference and Resistance Flashcards
what is electric current?
the flow of electrical charge.
state the equation linking charge, current and time.
Q = I 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 uised to calculate potential difference if current and resistance are known?
V = I R
potential difference (V), current (A), resistance (Ω)
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 electrocs as they flow through the metal, creating greater resistance to current flow
what is an ‘Ohmic Conductor’? state the condition required.
- a conductor for which current and potential difference are diectly 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 dependent resistors (LDRs)
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 thermistor’s resistance decreases.
give two examples of when a thermistor may 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
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 levels become too low, the light gains sufficient current to turn on
