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Question: Answered & Verified by Expert
On using red light $(\lambda=6600 Å)$ in Young's double slit experiment, 60 fringes are observed in the field of view. If violet light $(\lambda=4400 Å)$ is used, the number of fringes observed will be
PhysicsWave OpticsTS EAMCETTS EAMCET 2020 (10 Sep Shift 1)
Options:
  • A 30
  • B 120
  • C 60
  • D 90
Solution:
1205 Upvotes Verified Answer
The correct answer is: 90
Given, $\lambda_1=6600 Å, \lambda_2=4400 Å, n_1=60$
For same set up of YDSE,
$\begin{aligned}
n_1 \lambda_1 & =n_2 \lambda_2 \\
\Rightarrow \quad n_2 & =\frac{n_1 \lambda_1}{\lambda_2}=\frac{60 \times 6600}{4400}=\frac{60 \times 6}{4}=15 \times 6 \\
& =90 \text { fringes }
\end{aligned}$

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