9.5 I-V characteristics | 9.6 Diodes

What are the I-V characteristics for Resistors?

• P.D across resistor is directly proportional to the current in the resistor

• It’s an ohmic conductor as it obeys Ohm’s law

• The resistance of the resistor is constant.

• Straight line graph through the origin.

What are the I-V characteristics of filament lamps?

• The potential difference across a filament lamp is not directly proportional to the current through the resistor.

• It is non-ohmic

• Makes an s shape on graph.

• The resistance of the filament increases as the p.d across it increases. 

• This increase in resistance is caused by the wire getting so hot it glows. 

What is the explanation for the I-V characteristics of a filament lamp?

• As the current increases so does the rate of flow of charge through the filament- more electrons per second pass through it, so more collisions occur between the electrons and the positive metal ions per second.

• When the elctrons collide with the ions they transfer energy to the ions, causing the ions to vibrate more, or in other words to increase in temperature, and to collide still with more electrons.

What is a diode?

A component that only allows current in one particular direction. 

What is an LED?

A diode that emits light when they conduct. However, unlike most light sources, these LEDs emit light on a single specific wavelength.

What is a use for an LED?

As they are so efficient and take very little energy to run, they can be used as indicators of he direction through a part of a circuit.

What is the I-V characteristics for a diode?

• The potential difference across a diode (or LED) is not directly proprtional to the current through it. 

• A diode does not obey Ohm’s law, and so can be described as a non-Ohmic component. 

• The resistance of the diode is not constant.

• The diode’s behaviour depends on the polarity.

• The resistance is infinite when the polarity is correct.

• The diode does not conduct in the reverse direction.