1. Explain why electrons move from N region to P region going to the positive terminal of the battery.
2. Explain the mechanism how diodes and transistors are being used as switch.
1. When electrons move from the N region to the P region, they're actually moving in response to an electric field created by the battery. To understand why this happens, we need to look at the basic principles of a pn junction.
A pn junction is formed when a P-type semiconductor, which has positive charge carriers (holes), and an N-type semiconductor, which has negative charge carriers (electrons), are brought into contact. The P region has an excess of holes, while the N region has an excess of electrons.
When a battery is connected to the pn junction, its positive terminal repels the holes in the P region and attracts the electrons in the N region. This creates an electric field that acts as a barrier to the flow of current. This barrier is called the depletion region.
However, when the battery is connected in the forward bias configuration, the positive terminal is connected to the P region, and the negative terminal is connected to the N region. In this case, the positive terminal attracts the electrons in the N region, causing them to move toward the junction.
These electrons, which are the majority carriers in the N region, diffuse across the depletion region and combine with the holes in the P region. This results in the movement of negative charge (electrons) from the N region to the P region, creating a current flow from the N to the P region.
2. Diodes and transistors can be used as switches by exploiting their properties to control the flow of current. Here's a brief explanation for each:
Diodes:
A diode is a two-terminal device that only allows current to flow in one direction. It has two states: forward bias and reverse bias. In forward bias, the diode conducts current, acting as a closed switch. In reverse bias, the diode does not allow current to flow, acting as an open switch.
When a diode is connected in series with a load and a power source, such as a battery, in forward bias, current flows through the diode and the load. This allows the diode to act as a closed switch, completing the circuit. In reverse bias, the diode blocks current flow, acting as an open switch, and disrupts the circuit.
Transistors:
Transistors are three-terminal devices used as electronic switches or amplifiers. They consist of a base, collector, and emitter. There are two types of transistors: NPN (negative-positive-negative) and PNP (positive-negative-positive).
In its simplest form, a transistor acts as a switch when used in the cutoff and saturation regions. In the cutoff region, no current flows between the collector and emitter terminals, making the transistor act as an open switch. In the saturation region, current flows freely between the collector and emitter terminals, making the transistor act as a closed switch.
To use a transistor as a switch, you need to apply a suitable voltage or current to the base terminal. When the base current is sufficient, it allows the transistor to enter the saturation region and allow current flow. When the base current is absent or reduced, the transistor enters the cutoff region, blocking current flow.
By controlling the base current, you can turn the transistor on and off, allowing it to act as a switch to control the flow of current in a circuit.