3.5.1.2 Current-voltage characteristics Flashcards
What is Ohm’s law?
Provided physical conditions are kept constant, the current through an ohmic conductor is directly proportional to the potential difference across it
What does the I-V graph look like for an ohmic conductor?
Straight line through the origin
- gradient is constant
What physical factors affect resistance?
Light level and temperature
What does the gradient of an I-V graph tell you?
The resistance of a component, the shallower it is, the greater the resistance of the component (for an ohmic conductor)
What is an ideal voltmeter?
Has infinite resistance (no current flows through them)
What is an ideal ammeter?
Has zero resistance (no p.d. across them)
What is another word for ohmic conductors?
Metallic conductors
Describe the I-V graph for a filament bulb
As p.d. increases, so does the current, but at a decreasing rate. There is a non-linear correlation (curved line) With a changing positive gradient, where the gradient decreases. The p.d. is not directly proportional to the current
Why is the I-V graph for a filament lamp not directly proportional?
As temperature of the filament increases, resistance increases, so graph is curved. As the current is increased, the filament starts to heat up, causing an increase in lattice vibrations, therefore the rate of collisions increases so the resistance increases.
What is the I-V graph like for a diode?
As p.d. increases, current only flows after a certain threshold p.d. value (usually around 0.6 V). There is a non-linear correlation (curvy line) with a changing gradient (getting steeper). So the p.d. is not directly proportional to current
Why is current not directly proportional to voltage in a diode?
Current only flows in one direction and once current flows, resistance decreases.
What is reverse bias?
Where the diode doesn’t allow current to flow because resistance is infinitely large or the current is very small - in the mA or microA range
What is forward bias?
Where the diode allows the flow of current because resistance is small
What is a diode used for?
Current rectification
