(2) Current, P.D and Resistance Flashcards
What does the ammeter measure?
Current
What does the voltmeter measure?
Potential difference (voltage)
What is electric current?
Electric current is the flow of electrical charge
Equation for charge flow
Charge flow= current x time
(Q=I x t)
Charge flow= Coulombs (C) Current= Amps (A) Time= Seconds
What can be said about the value of current at any point in a single closed loop?
Current is caused by a source of potential difference, it has the same value at any point in a single closed loop of a circuit
What 2 factors does the current in a circuit depend on?
- Potential difference (V)
- Resistance (R)
Equation for P.D, current and resistance
P.D= current x resistance
(V= I x R)
P.D= Volts Current= Amps Resistance= ohms
Define an ohmic conductor
An ohmic conductor is
- a conductor for which 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
- Lamps
- Diodes
- Thermistors
- LDRs (light dependent resistors)
What happens to the resistance of a thermistor as temperature decreases?
The resistance decreases
What is different about current flow through a diode?
Current only flows in one direction
(Resistance is very high in the other direction preventing current flow)
Give 2 examples of when a thermistor may be used
- A thermostat
- A freezer (to turn on a cooler when the temperature gets too high)
What happens to the resistance of a filament lamp as the temperature increases?
The resistance increases
(As the current through the lamp increases, the filament gets hotter and has a higher resistance)
What happens to the resistance of a LDR as light intensity decreases?
The resistance increases
How could a LDR be used?
• street lamp
(When light levels become low it gains sufficient current to turn on)
