Question

When a light ray from a rarer medium is refracted into a denser medium, its

• A. Speed increases, wavelength increases
• B. Speed decreases, wavelength increases
• C. Speed increases, wavelength decreases
• D. Speed decreases, wavelength decreases

Answer 1

The correct option is D Speed decreases, wavelength decreases

When a light ray goes from rarer to denser medium (optical denser), its speed decreases.
From relation, $v=f\lambda$
$f\to$ constant (as source remains same)
$\Rightarrow \upsilon$ ∝ $\lambda$
or $\lambda \downarrow$ because $v\downarrow$ in denser medium

Tip: Frequency of a wave is dependent on source only. $\frac{v}{\lambda }=$ constant, provided the source doesn't change.