Electronics

Step 1: Forward bias.
- External voltage is applied such that -side is connected to positive and -side to negative terminal of the battery.
- Barrier potential decreases, width of depletion layer reduces.
- Large current flows due to movement of majority carriers.
- Resistance is very low.
Step 2: Reverse bias.
- External voltage is applied such that -side is connected to negative and -side to positive.
- Barrier potential increases, width of depletion layer widens.
- Very small current flows due to minority carriers (called leakage current).
- Resistance is very high.
Step 3: Biasing in solar cell.
A solar cell works in reverse bias mode. Light falling on the junction creates electron-hole pairs which are separated by the built-in field, producing emf.
Step 4: Conclusion.
Thus, forward bias allows large current, reverse bias allows negligible current, and solar cells operate under reverse bias.

Step 1: Nature of LED.
LED (Light Emitting Diode) is a - junction diode designed to emit photons when carriers recombine.
Step 2: Forward bias action.
When forward biased, electrons from the -region and holes from the -region recombine at the junction. This recombination releases energy in the form of light.
Step 3: Reverse bias case.
In reverse bias, the LED blocks current, and no recombination (hence no light) occurs.
Step 4: Conclusion.
Thus, LEDs must be kept forward biased for light emission.

Step 1: Principle.
A transistor oscillator works on the principle of positive feedback. The output of an amplifier is fed back to its input in phase to maintain continuous oscillations.
Step 2: Essential components.
- A transistor amplifier.
- Feedback network (usually LC tank circuit).
- DC power supply.
Step 3: Working process.
1. When supply is given, noise voltage in the circuit provides initial signal.
2. The LC tank circuit produces oscillations of its natural frequency.
3. The transistor amplifies these oscillations.
4. A part of output is fed back in phase with the input, reinforcing it.
5. Continuous undamped oscillations are maintained.
Step 4: Barkhausen criterion.
For sustained oscillations:
Step 5: Circuit diagram.
(Insert diagram of transistor oscillator: LC tank circuit at input, transistor amplifier, feedback loop).
Step 6: Conclusion.
Thus, a transistor oscillator converts DC power into continuous AC output of a desired frequency.

Step 1: Principle.
A p-n junction diode allows current only during forward bias. In full-wave rectifier, two diodes conduct alternately for each half cycle of AC input.

Step 2: Circuit arrangement.
- A center-tapped transformer provides AC input.
- Two diodes and are connected across the secondary.
- Load resistance is connected across the output.

Step 3: Working process.
1. During the positive half cycle of input AC:
- Upper half of secondary is positive.
- conducts (forward biased), is reverse biased.
- Current flows through in one direction.
2. During the negative half cycle of input AC:
- Lower half of secondary is positive.
- conducts (forward biased), is reverse biased.
- Current again flows through in the same direction.

Step 4: Output.
Both halves of input AC are converted into pulsating DC. The frequency of output is double the input frequency.
Step 5: Circuit diagram.
(Insert standard full-wave rectifier diagram with center-tapped transformer and two diodes).

Step 6: Conclusion.
Thus, the full-wave rectifier efficiently converts AC into DC, utilizing both halves of input.