6.4 I-V Characteristics Flashcards
What are I-V characteristics?
A graph which shows how the current (I) flowing through a component changes as the potential difference (V) across it is increased.
What is the relationship between the gradient of a characteristic I-V graph and the resistance?
The shallower (smaller) the gradient of an I-V graph, the greater the resistance of the component
How would you find the characteristic I-V graph for a component?
- use a circuit made up of a power pack, variable resistor, component, ammeter and voltmeter (around the component)
- vary the resistance of the variable resistor
- record a range of current and voltage values and plot an I-V graph using them
What is the assumption for an ideal voltmeter?
That they have an infinite resistance, so no current flows through them
What is the assumption for an ideal ammeter?
They have no resistance, so no potential difference flows across them
What does an I-V graph look like for an ohmic conductor(under constant physical conditions)?
The current is directly proportional to the voltage, so their characteristic graph is a straight line through the origin as their resistance doesn’t change.
What does an I-V graph look like for a filament lamp?
A curve that stats steep but gets shallower as the voltage rises. The current flowing through the filament lamp increases its temperature, which increases the resistance of the lamp.
Why does the current flowing through a filament lamp increases its temperature?
When a current flows through a metal conductor, some of the electrical energy is transferred into heat energy and causes the metal to heat up.
This extra heat energy causes the particles in the metal to vibrate more.
These vibrations make it more difficult for charge-carrying electrons to get through the resistor.
The current can’t flow as easily and the resistance increases.
Is there a limit to the amount of current that can flow through a resistor?
For most resistors there is a limit to the amount of current that can flow through them
More current means an increase in temperature, which means an increase in resistance, which means the current decreases again
What does the I-V graph look like for a diode?
Diodes are made from semiconductors and are designed to let current flow in one direction only
Forward bias is the direction in which the current is allowed to flow
What part of the circuit symbol indicates which direction the diode will let current flow?
The triangle in the circuit symbol
What is the threshold voltage for a diode?
Most diodes require a voltage of about 0.6V in the forward direction before they will conduct - this is called the threshold voltage
What happens when a diode is in reverse bias?
The resistance of the diode is very high and the current that flows is very tiny
