A p-n photodiode is fabricated from a semiconductor with a band gap of 2.5 eV . It can detect a signal of wavelength

Correct answer: D. 4000 Å Key Idea Only signals having wavelength less than threshold wavelength will be detected. Energy aligned & E=hv=h c λ & λ= hc E aligned λ= hc E Substituting the values of and in the above equation λ= 6.6 × 10^ -34 × 3 × 10^8 2.5 × 1.6 × 10^ -19 = 5000 Å As 4000 Å 5000 Å Signal of wavelength 4000 Å can be detected by the photodiode.

NEET 2009

Exam: NEET
Year: 2009
Subject: Physics
Chapter: Semiconductors

NEET 2009 · Physics · Semiconductors

A p-n photodiode is fabricated from a semiconductor with a band gap...

p-n

photodiode is fabricated from a semiconductor with a band gap of

2.5 \mathrm{eV}

. It can detect a signal of wavelength

Options

A $6000 Å$
B $4000 \mathrm{~nm}$
C $6000 \mathrm{~nm}$
D $4000 Å$

Correct answer

D. $4000 Å$

Step-by-step solution

Key Idea Only signals having wavelength less than threshold wavelength will be detected. Energy

\begin{aligned}& \mathrm{E}=\mathrm{hv}=\mathrm{h} \frac{\mathrm{c}}{\lambda}\\ & \lambda=\frac{\mathrm{hc}}{\mathrm{E}} \end{aligned}

\Rightarrow \quad \lambda=\frac{\mathrm{hc}}{\mathrm{E}}Substituting the

values of and in the above equation \lambda=

\frac{6.6 \times 10^{-34} \times 3 \times 10^8}{2.5 \times 1.6 \times 10^{-19}}=

5000 Å As

4000 Å \lt 5000 Å

Signal of wavelength

4000 Å$ can be detected by the photodiode.

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