Consider the following statements :
A. The junction area of solar cell is made very narrow compared to a photo diode.
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 continuous increase of LED light intensity.
E. LEDs have to be connected in forward bias for emission of light.
Choose the correct answer from the options given below :

Solution

Physics sir · 2 steps

Check each statement against how the device works: a solar cell harvests light, an LED emits it.

1. Two devices. A solar cell turns light into power on its own, so it needs a large area to catch light and no battery. An LED turns forward current into light when electrons and holes recombine at the junction.

   Statement	True or false	Reason
   A	False	A solar cell has a wide junction area to collect as much sunlight as possible. A photodiode is the one kept small.
   B	True	The solar cell itself produces the emf. No external bias is applied.
   C	False	An LED is made of a heavily doped p-n junction, so that many electrons and holes recombine and give out light.
   D	False	Intensity rises with forward current only up to a maximum. Beyond that, more current makes the light weaker.
   E	True	Light comes from recombination, which happens only when the LED is forward biased.

2. So. Only B and E are correct, which is option (b).

The idea to keep. Solar cell: large area, no bias. Photodiode: small area, reverse bias. LED: heavily doped, forward bias, and its brightness peaks at some current and then falls.

Answer from the NTA final answer key. Solution by PrepWiser.