Basic Electronics
DEMONSTRATING HOW A TRANSISTOR CAN BE USED TO SLOWLY CHARGE AND DISCHARGE A CAPACITOR
A batter of 9V, three resistors of resistances (470Ω, 100KΩ, 3.3KΩ), one LED, one switch, one NPN transistor, one capacitors of 100µF and a connecting wire.
Diagram showing the electrical circuit and component arrangement
The various components are connected in a circuit as shown above in the diagram. The switch is closed and opened to observe what will happen to the LED. The resistors are replaced with other ones of different resistance values and then observe what happens. The capacitor is also charged and replaced with different capacitors to observe the outcome.
Observation:
When the switch was closed the LED lit slowly, flashes and then goes off. When other resistors of lower resistances were used it took a larger time before the LED flashes and went off.
Discussion:
The LED slowly lit, flashes and goes off as a result of the gradual charging, then when it attains a maximum capacitance the LED fight brightly for a very brief second in a flash. It goes off because the capacitor that becomes fully charged up opens the circuit so that the LED does not receive any current thus it gives off. Large capacitors became fully charge over a long time so will lit more slowly than a smaller one. Large capacitors discharge large current so produced a brighter and larger flash than a smaller one. However, for smaller capacitors, it charges slowly but faster than a larger one. The smaller capacitors discharged smaller current resulting in less bright flash.
THE USE OF THE CHARGING AND DISCHARGING BEHAVIOUR OF CAPACITORS IN THE FLASH LIGHT OF CAMERAS
When a capacitor becomes fully charged, it takes less than a second for it discharge completely whiles a battery takes some minute or hours to discharge fully. This is the reason why the flash lights of cameras use capacitors. The capacitor becomes charged up by battery of camera, then it discharges the full charge into the light at the same time the picture is being taken, it is the full discharge of the capacitor just within a second or less and that results in lighting the flash bulb so brightly for less than a second.