Answer
The correct answer is:
(d) $f$ does not change, $\lambda$ increases
Work Step by Step
When an EM wave passes from one medium into another medium, the frequency does not change.
We can write an expression for $\lambda_1$:
$\lambda_1 = \frac{v_1}{f}$
We can write an expression for $\lambda_2$:
$\lambda_2 = \frac{v_2}{f}$
Since $v_2 \gt v_1$, then $\lambda_2 \gt \lambda_1$
The correct answer is:
(d) $f$ does not change, $\lambda$ increases
