Question

What is the frequency of red light having wave length $750 \text{ nm}$ ?

• A. $3.0 \times 10^{14} \text{ Hz}$
• B. $4.0 \times 10^{14} \text{ Hz}$
• C. $7.5 \times 10^{14} \text{ Hz}$
• D. $9.0 \times 10^{14} \text{ Hz}$

Hint:

Shortcut: $\nu = \frac{3 \times 10^8}{\lambda (\text{in m})}$

Answer 1

The Correct Option is B

Concept: Relation between speed, wavelength and frequency: \[ c = \nu \lambda \Rightarrow \nu = \frac{c}{\lambda} \]

Step 1: Convert wavelength. \[ 750 \text{ nm} = 750 \times 10^{-9} \text{ m} \]

Step 2: Substitute values. \[ \nu = \frac{3 \times 10^8}{750 \times 10^{-9}} \]

Step 3: Calculate. \[ \nu = \frac{3}{750} \times 10^{17} = 4 \times 10^{14} \text{ Hz} \]

Step 4: Conclusion.
Frequency = $4.0 \times 10^{14}$ Hz. Final Answer: Option (B)