Topic 10 – Electricity and Circuits- Resistance 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 the current in a circuit be varied?
Using a variable resistor.
Give the equation linking current with resistance
p.d. (V) = current (A) x resistance (Ω) V = IR
How is 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 current and potential difference 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.
- Filament lamps
- Diodes
- Thermistors
- Light Dependant Resistors (LDRs)
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
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
