Question

23. A radiation has wavelength 4650 Å. Its waves
number and frequency is -
(A)4.650 X 10-5cm-1 and 3.0 x 100 cm s-1
(B) 2.150 x 10cm-1 and 6.45 X 1024 Hz
(C) None of these
(0)2.325 x 10-5cm-1 and 6.0 x 10 cm s-1
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Answer 1

wave number is inverse of wavelength.

or, $\bar{\nu}=\frac{1}{\lambda}$

= 1/(4650 A°)

= 1/(4650 × 10^-10) cm-¹

= 10^10/4650 cm-¹

= 100,000 × 10^5/4650 cm-¹

= 21.5 × 10^5 cm-¹

= 2.15 × 10^6 cm-¹

we know, wavelength × frequency = velocity of light

or, 4650 × 10^-10 × frequency = 3 × 10^8

or, frequency = 3 × 10^8/4650

= 30000 × 10¹⁴/4650

= 6.45 × 10¹⁴ Hz