I-V Characteristics Flashcards
What is the relationship between the gradient of a. I-V graph and the resistance of the component?
The shallower the gradient of the characteristic I-V graph, the greater the resistance of the component.
What is an I-V characteristic?
A graph where current is plotted against potential difference.
What does a curved I-V characteristic show?
The resistance is changing.
Describe the method of finding the I-V characteristic of a component.
- set up a circuit where the ammeter is in series to the component and the voltmeter is in parallel to the component.
- use the variable resistor to decrease/increase the resistance of the circuit in small, equal steps. For each change, take a reading from the ammeter and the voltmeter.
- reverse the direction of electricity flow by switching the wires connecting to the power pack to collect data for negative values of V and I.
- plot the data on a pair of axes.
What is the I-V characteristic of a metallic conductor given that they obey ohms law?
A straight line passing through the origin where the current is directly proportional to the potential difference.
What does the I-V graph for a filament look like?
A curve that starts steep but gets shallower as the voltage rises. It is an “S” shape graph.
A filament is a thin coil of metal wire, so why is the I-V graph not the same as the I-V graph of a metallic conductor?
Some of the current flowing through the filament lamp is transferred into heat energy and causes the metal to heat up - meaning the filament lamp does not obey ohms law.
Why does the extra heat in a filament lamp result in an increasing resistance?
The particles in the metal vibrate more due to the extra heat. These vibrations make it more difficult for the electrons, that are carrying the charge, to get through the resistor. The current can’t flow easily and the resistance increases.
Why does the I-V graph for the filament lamp level off at high currents?
The more current passing through the filament lamp, the greater the increase in temperature, resulting in an increase in resistance, meaning the current decreases again.
What is a semiconductor?
A group of materials which conduct electricity (but not as well as metals).
What happens when a superconductors temperature rises?
They can release more charge carriers and their resistance decreases.
Name three semiconductor components.
- thermistors
- diodes
- LDR’s
What is a thermistor?
A component with a resistance that depends on it’s temperature.
What are NTC thermistors?
Negative temperature coefficient thermistors. Their resistance decreases as the temperature goes up.
How is data collected for an I-V curve for a thermistor?
- measure the resistance at different temperatures.
- continue with the method used for finding the I-V characteristic of any other component.
