<p>(a) Three photodiodes D1, D2, and D3 are made of semiconductors having band gaps of 2.5 eV, 2 eV, and 3 eV respectively. Which of them will not be able to detect light of wavelength 600 nm?</p>

<p>(b) Explain the working principle of an LED with a neat diagram.</p>

<p>(c)&nbsp;State any two applications of LEDs.&nbsp;</p>

<p>(d) Propose a project using LEDs to solve a community lighting problem</p>