Question

Consider the following statements: 
A. The junction area of a solar cell is made very narrow compared to a photodiode.
B. Solar cells are not connected with any external bias. 
C. LED is made of lightly doped p-n junction.
D. Increase of forward current results in a continuous increase in LED light intensity. 
E. LEDs have to be connected in forward bias for emission of light.

• A. B, D, E Only
• B. A, C Only
• C. A, C, E Only
• D. B, E Only

Hint:

Remember that in LEDs, forward bias is essential for the emission of light. Solar cells, on the other hand, generate voltage without the need for external bias.

Answer 1

The Correct Option is D

To solve the given problem, we need to evaluate each of the statements provided and determine their validity regarding solar cells, photodiodes, and LEDs. Let's analyze each statement one by one: 

1. Statement A: "The junction area of a solar cell is made very narrow compared to a photodiode."

This statement is incorrect. The junction area of a solar cell is usually larger to absorb more sunlight and generate more current, whereas in a photodiode, the focus is on speed and sensitivity, often involving a more optimized design for specific applications.

1. Statement B: "Solar cells are not connected with any external bias."
2. Statement C: "LED is made of lightly doped p-n junction."

This statement is incorrect. LEDs are typically made with heavily doped p-n junctions to facilitate electron-hole recombination, which is necessary for efficient light emission.

1. Statement D: "Increase of forward current results in a continuous increase in LED light intensity."

This statement can be seen as generally true, but there are limitations at maximum current ratings where further increases can damage the LED or cause efficiency droop (a decrease in efficiency with increased current). However, in typical operating ranges, this statement holds true.

1. Statement E: "LEDs have to be connected in forward bias for emission of light."

This statement is correct. LEDs need to be forward-biased to allow charge carriers to recombine and emit light.

Based on the analysis above, the correct statements are B and E. Therefore, the correct answer is: B, E Only.

Answer 2

Let's analyze each statement:

Statement A:

The junction area of a solar cell is made very narrow compared to a photodiode.

This statement is incorrect. Solar cells generally have a larger junction area than photodiodes to capture more sunlight. The increased junction area allows the solar cell to absorb more light and generate more electricity.

Statement B:

Solar cells are not connected with any external bias.

This statement is correct. Solar cells generate their own voltage and current when exposed to light, so they do not require an external bias. The energy from the sunlight is converted directly into electrical energy by the photovoltaic effect.

Statement C:

LED is made of a lightly doped p-n junction.

This statement is incorrect. LEDs are made of heavily doped p-n junctions to enhance radiative recombination. The heavy doping allows for efficient electron-hole recombination, which results in the emission of light.

Statement D:

Increase of forward current results in a continuous increase of LED light intensity.

This statement is incorrect. The light intensity of an LED increases with forward current up to a certain point. After that point, the intensity may saturate or even decrease due to heating effects and the LED’s characteristic behavior.

Statement E:

LEDs have to be connected in forward bias for emission of light.

This statement is correct. LEDs emit light when connected in forward bias because electrons and holes recombine in the depletion region, releasing energy as photons (light).

Conclusion:

The correct statements are B and E. Therefore, the correct answer is \( \boxed{4} \) (B, E Only).