Understanding LDR, NTC, PTC, LED Diodes, and Semiconductor Crystals

LDR (Light Dependent Resistor): These are resistors whose resistance value changes when illuminated by light (visible or invisible, such as ultraviolet or infrared).

LDR Features:

1. Its resistance value depends on the amount of light that strikes it.
2. Ohm's Law does not apply directly.
3. Typically made from cadmium sulfide. This material, when kept in the dark, has very few free electrons, resulting in high resistance. However, when illuminated, it releases electrons, decreasing the resistance. This makes it a photoconductor.
4. Manufacturers provide values such as resistance in total darkness (R), resistance under illumination (e.g., 1000 lux), permissible maximum stress, and maximum power.
5. Can be used in lighting systems as detectors.

NTC (Negative Temperature Coefficient) Thermistors: These are resistors whose nominal resistance value decreases as temperature increases.

NTC Features:

1. As temperature increases, the resistance value decreases.
2. Ohm's Law does not apply directly.
3. Made from semiconductor oxides of chromium, magnesium, and similar materials.
4. Available in various shapes, such as disks.
5. Manufacturers provide a range of extreme values to consider when working with them (e.g., at 25°C).
6. Can be used as temperature sensors.

PTC (Positive Temperature Coefficient) Thermistors: These are resistors whose resistance value increases with increasing temperature.

PTC Features:

1. Ohm's Law does not apply directly.
2. Manufactured using materials such as barium carbonate, oxide, or titanium oxide.
3. Like NTC thermistors, they can be used as temperature sensors.

LED (Light Emitting Diode): An electronic component that emits light when an electric current passes through it. They are commonly used as indicator lights in electronic equipment. LEDs are robust electronic components and consume very little energy.

N-Type Semiconductor Crystals: N-type crystals are conductive because impurity atoms contribute electrons that can move freely and transmit the flow of electrons from an external circuit effectively.

P-Type Semiconductor Crystals: In a P-type crystal, impurity atoms create electron vacancies (holes) in the crystal structure. Electrons can move from one atom to another using these holes.

The process of introducing impurities into a semiconductor crystal is called doping, and the elements used are called dopants.

PN Junction: When an N-type semiconductor crystal is in contact with a P-type semiconductor crystal and connected in a circuit, a unique phenomenon occurs: electrons can move in one direction, from the N-type crystal to the P-type crystal.