Description
The Photo Transistor Characteristics Apparatus is a laboratory device designed for studying the response of a phototransistor when exposed to varying light intensities and collector-emitter voltages, allowing learners to plot and understand its V-I characteristics and light sensitivity.
Apparatus Description
The apparatus typically includes a phototransistor mounted on a panel, a regulated DC power supply (usually 0–10 V), analog meters (voltmeter and ammeter), and a controllable light source such as an LED or bulb.
Some setups use an optical bench or adjustable mount to change the distance/light intensity incident on the phototransistor.
Principle and Working
A phototransistor is a light-sensitive transistor whose collector-base junction is exposed to light. When light falls on the base junction, it generates a photo-induced current, causing the collector current to increase in proportion to light intensity.
This generates greater amplification (gain) than a photodiode, making phototransistors very responsive to changes in light conditions.
Experimental Procedure
The light source is adjusted at various intensities.
For each incident light level, the collector-emitter voltage is changed in steps, and the corresponding collector current is measured using the meters.
The result is a family of V-I curves for the phototransistor at different light intensities, demonstrating its sensitivity and photo-amplification properties.
Applications
Phototransistor characteristic studies are fundamental in understanding optoelectronic devices, as these sensors are widely used in object detection, optical switches, counters, and communication systems.
This apparatus is important in physics, electronics, and engineering laboratories for hands-on study of light-controlled electronic components.