Daily review: LED (Light Emitting Diode)…

Q: Which physical process is responsible for the light emission in an LED?

Electroluminescence — Electroluminescence occurs when charge carriers recombine in a semiconductor, releasing energy as photons.

Q: In what mode of bias is a photodiode typically operated for light detection?

Reverse bias — Photodiodes are operated in reverse bias to minimize dark current and improve sensitivity to incident light.

Q: What determines the color (wavelength) of the light emitted by an LED?

The bandgap energy of the semiconductor material — The photon energy emitted equals the bandgap energy (Eg) of the semiconductor material.

Q: What is the primary function of a photodiode?

To convert optical energy into electrical current — Photodiodes are sensors that convert light into an electrical current (photocurrent).

Q: When an LED is forward-biased, what happens at the P-N junction?

Electrons and holes recombine — Recombination of electrons and holes at the junction releases energy in the form of light.

Q: Which material is NOT commonly used in the construction of visible spectrum LEDs?

Silicon (Si) — Silicon is an indirect bandgap semiconductor, making it inefficient for standard visible light emission.

Q: What is 'dark current' in a photodiode?

Current that flows when there is no incident light — Dark current is the small reverse leakage current that flows even when no light is present.

Q: Why is a series resistor (ballast resistor) required when connecting an LED to a power source?

To limit the current and prevent damage — LEDs are current-controlled devices; a resistor prevents thermal runaway by limiting the forward current.

Q: How does the photocurrent of a photodiode change with increasing light intensity?

It increases linearly — The photocurrent is directly proportional to the intensity of the incident light.

Q: What happens if an LED is connected in reverse bias?

It does not conduct and may be damaged if V exceeds PIV — An LED acts as an open circuit in reverse bias; exceeding the Peak Inverse Voltage (PIV) causes breakdown.

Question 1 of 10

Which physical process is responsible for the light emission in an LED?

Electroluminescence occurs when charge carriers recombine in a semiconductor, releasing energy as photons.

Question 2 of 10

In what mode of bias is a photodiode typically operated for light detection?

Photodiodes are operated in reverse bias to minimize dark current and improve sensitivity to incident light.

Question 3 of 10

What determines the color (wavelength) of the light emitted by an LED?

The photon energy emitted equals the bandgap energy (Eg) of the semiconductor material.

Question 4 of 10

What is the primary function of a photodiode?

Photodiodes are sensors that convert light into an electrical current (photocurrent).

Question 5 of 10

When an LED is forward-biased, what happens at the P-N junction?

Recombination of electrons and holes at the junction releases energy in the form of light.

Question 6 of 10

Which material is NOT commonly used in the construction of visible spectrum LEDs?

Silicon is an indirect bandgap semiconductor, making it inefficient for standard visible light emission.

Question 7 of 10

What is 'dark current' in a photodiode?

Dark current is the small reverse leakage current that flows even when no light is present.

Question 8 of 10

Why is a series resistor (ballast resistor) required when connecting an LED to a power source?

LEDs are current-controlled devices; a resistor prevents thermal runaway by limiting the forward current.

Question 9 of 10

How does the photocurrent of a photodiode change with increasing light intensity?

The photocurrent is directly proportional to the intensity of the incident light.

Question 10 of 10

What happens if an LED is connected in reverse bias?

An LED acts as an open circuit in reverse bias; exceeding the Peak Inverse Voltage (PIV) causes breakdown.

Daily review: LED (Light Emitting Diode) | Photodiode Quiz