Grade 10 electricity – Semiconductor Diodes Quiz

A diode is a semiconductor device that conducts current easily in one direction (forward) and blocks it in the opposite direction (reverse), so it acts as a one-way valve for electric current.

The diode symbol is a triangle pointing to a line. When forward-biased, conventional current flows in the direction of the arrow—from the anode (triangle) to the cathode (line).

P-type semiconductor is doped with acceptor atoms that create 'holes' (places where an electron is missing). These holes act as the majority carriers in P-type material.

Forward bias pushes holes and electrons toward the junction, reducing the depletion region and lowering the barrier so charge carriers can cross the junction and current flows.

Reverse bias pulls carriers away from the junction, widening the depletion region and preventing current, except for a very small leakage current until breakdown occurs.

A silicon diode requires roughly 0.6–0.7 V forward voltage to overcome the junction barrier and start conducting significantly.

A Zener diode is made to have a well-defined breakdown (Zener) voltage in reverse bias and is used to provide a stable reference or to regulate voltage.

An LED is a diode that converts electrical energy into light when forward-biased; electrons recombine with holes and release energy as photons (light).

An LED needs a resistor in series to limit current to a safe value; without it the LED can draw too much current and be damaged.

A full-wave bridge rectifier uses four diodes arranged in a bridge so both halves of the AC waveform produce a unidirectional output.

A photodiode converts light into electrical current; when light falls on its junction it creates electron–hole pairs and a measurable current flows, useful as a sensor.

Avalanche breakdown occurs under high reverse voltage when carriers gain enough energy to create more carriers by collision, causing a sudden rise in reverse current; Zener diodes use controlled breakdown.

Schottky diodes use a metal–semiconductor junction giving a lower forward voltage (about 0.2–0.4 V) and faster switching speed than regular silicon PN-junction diodes.

In reverse bias a diode blocks current and only a tiny leakage current (microamps or less) flows until breakdown voltage is reached.

In the diode symbol the triangle (arrow) points toward the line; the arrow end is the anode (positive side when forward-biased) and the line is the cathode.

At the PN junction electrons and holes meet and recombine, leaving behind charged donor and acceptor ions that form the depletion region with no free carriers.

Diodes are commonly used as rectifiers in power supplies to change AC from the mains into DC for electronic devices such as phone chargers and radios.

After the forward threshold (about 0.7 V for silicon), small increases in voltage produce large increases in forward current because the junction conducts more easily.

Most common diodes are made from silicon that has been doped to form P-type and N-type regions, creating the PN junction needed for diode action.

Doping introduces extra carriers (electrons or holes) into the semiconductor, increasing its conductivity by providing more charge carriers to carry current.

A diode can be used to block reverse current from the battery to the charger, protecting the charger and preventing battery discharge back through the supply.

A diode shows a non-linear I–V curve: a tiny reverse leakage current until breakdown, and in forward bias, current remains small until the threshold voltage then increases rapidly.

A diode in a torch prevents reverse currents that could discharge the battery or damage components, allowing current flow only toward the bulb or LED.

Forward bias means the anode is made more positive relative to the cathode, which reduces the barrier and allows current to flow through the diode.

Diodes do not convert DC to AC by themselves. They are used for rectification, indication, and regulation, but generating AC from DC requires additional circuitry such as oscillators or inverters.

A silicon diode needs about 0.6–0.7 V to turn on; with 1.5 V forward across it, it will conduct and current will flow (limited by the rest of the circuit).

Diodes have a maximum reverse voltage rating; exceeding it can cause breakdown and damage. Designers limit reverse voltage or add protective components like clamps or voltage dividers.

When current flows through a diode there is a voltage drop across it; the product of current and voltage drop (power) becomes heat, so diodes can warm during normal operation.