3.5.1.2 Current-Voltage Characteristics Flashcards
To revise Electricity for AQA A Level Physics
What does the gradient of an I/V graph show?
The gradient of an I/V graph represents the reciprocal of the resistance (1/R).
What does the gradient of a V/I graph show?
The gradient of a V/I graph shows the resistance of a component.
Describe a brief method of how you would investigate the I/V characteristics of a component.
- Connect the component to the source of potential difference.
- Connect an ammeter in series with the component.
- Connect a rheostat/variable resistor in series with the component.
- Connect a voltmeter in parallel across the component.
- Vary the current through the component using the rheostat.
- Start at the highest setting and decrease the resistance in regular intervals.
- Every time you decrease the resistance, record the reading of the voltmeter and ammeter.
- After taking multiple readings, plot a graph of current against potential difference (I/V).
Describe the I/V graph of an ohmic conductor.
Straight line through the origin. Linear relationship between current and potential difference.
What does a steep gradient on a I/V graph represent?
What does a shallow gradient on a I/V graph represent?
A steep gradient means that the resistance of the component is low.
A shallow gradient on a I/V graph means that the resistance of the component is high.
What does a shallow gradient on a V/I graph represent?
What does a steep gradient on a V/I graph represent?
A shallow gradient of a V/I graph represents that the resistance of the component is low.
A steep gradient on a V/I graph represents that the resistance is high.
What needs to be constant for the current and potential difference to be proportional for an ohmic conductor?
External/Physical conditions such as temperature and light intensity need to remain constant.
Describe the I/V graph for a filament lamp.
The graph is a curve that starts steep but gets shallower as the potential difference increases.
Why does the graph curve?
The graph curves because the filament in the lamp heats up, due to an increase of current, so the resistance increases.
This means that the current will increase at a lower rate than potential difference.
What increase the temperature of the filament?
The high current increases the temperature of the filament.
Why is a filament lamp not an example of an ohmic conductor?
Because the current through it and the potential difference across is are not directly proportional.
Why does the metal filament within the lamp heat up, and why does this cause an increase of resistance?
When a current flows through a metal filament, some of the electrical energy is transferred into heat energy and causes the metal to heat up.
The increase in heat energy, causes the internal energy of the particles to increase, thus increasing their kinetic energy,
The increase in kinetic energy causes the particles to vibrate more.
This makes it harder for charge carriers to pass through the metal filament, so current can not flow as easily, Therefore the resistance has increased.
What are diodes made from?
Semiconductors
What is a diode designed to do?
They are designed to let current flow in one direction only.
What is Forward Bias? How can you tell what is the Forward Bias from a circuit diagram?
The forward bias is the direction in which the current is allowed to flow.
This is shown by the direction of the triangle in the circuit symbol.
