What is an I/V characteristic?
A graph of I against V, which shows how the current ( I ) flowing through a component changes as the potential difference ( V ) across it is increased.
What is a cell?
A source of electrical energy.
What is a diode?
A component which allows current in one direction only.
How does the resistance of a thermistor vary?
Decreases with increasing temperature.
How does the resistance of a LDR vary?
Decreases with increasing light intensity.
How can you measure the variation of current with pd for a component?
Using a:
• Potential divider to vary the pd from zero
• A variable resistor to vary the current to a minimum
What is an advantage of using a potential divider?
- The current through the component and the pd across it can be reduced to zero.
- This isn’t possible with a variable resistor circuit.
How does the resistance of a metal vary with temperature?
• The resistance of a metal increases with increase of temperature.
Why does the resistance of a metal increase with an increase in temperature?
- Positive ions in the conductor vibrate more when its temperature is increased.
- Charge carriers ( conduction electrons ) cannot pass through the metal as easily when a pd is applied across the conductor.
What does it mean for a metal to have a positive temperature co efficient?
When its resistance increases with an increase of temperature.
How does the resistance of an intrinsic semi conductor vary with temperature?
- Number of charge carriers ( conduction electrons ) increases when the temperature is increased
- A thermistor made from an intrinsic semi conductor therefore has a negative temperature co efficient.
What does it mean for an intrinsic semi conductor to have a low temperature co efficient?
Resistance decreases with an increase of temperature.
What is a thermistor?
A resistor with a resistance that depends on its temperature.
What is a negative temperature co efficient?
Resistance decreases as the temperature goes up.
What is the I/V characteristic for an NTC thermistor?
- Curves upwards.
- Increasing the current through the thermistor increases its temperature
- Increasing gradient of this characteristic graph tells you that the resistance is decreasing.
- V/I characteristic is the opposite.
What does heating up a thermistor do?
• Gives more electrons enough enough energy to escape from their atoms, which means there are more charge carriers available, decreasing the resistance.
What do diodes do?
Let current flow in one direction onlu.
What is forward bias ( diodes )?
Direction in which the current is allowed to flow.
What is the threshold voltage of diodes?
Voltage in the forward direction before they will conduct.
Most diodes have a threshold voltage of 0.6 volts.
What is reverse bias ( diodes )?
Resistance of the diodes is very high, therefore the current that flows in the forward direction is very tiny.
What is the I/V characteristic for a filament lamp, and why?
- Curve that starts steep, but gets shallower with voltage increase.
- Current flowing through the lamp increases its temperature.
- Resistance of a metal increases as the temperature increases.
What is the filament?
Coiled up length of metal wire.
