## College Physics (4th Edition)

The correct answer is: (d) $f$ does not change, $\lambda$ increases
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