Question

Two source of light of wavelength 2500Å and 3500Å are used in Young’s double slit experiment simultaneously. Which orders of fringe of two wavelength patterns coincide?

• A. 3^rd order or1^st source and 5^th of the 2^nd
• B. 7^rd order or1^st source and 5^th of the 2^{nd \}
• C. 5^rd order or1^st source and 5^th of the 2^nd
• D. 5^rd order or1^st source and 5^th of the 2^nd

Answer 1

Answer: (B)

7^rd order or1^st source and 5^th of the 2^{nd \}

Answer 2

: Let $n^{th}$fringe of 2500 Å coincide with $(n - 2)^{th}$ fringe of 3500Å

$\therefore 3500(n - 2) = 2500 \times n$

$1000n = 7000,orn = 7$

$\therefore$ $7^{th}$order fringe of $1^{st}$source will coincide with $5^{th}$order fringe of $2^{nd}$source