Question

When medium of electromagnetic waves changes from air to water, their speed

• A. increases.
• B. remains same
• C. decreases.
• D. may increase or decrease.

Answer 1

The correct option is C decreases.

When medium of electromagnetic waves changes from air to water, then speed decreases because

$c=\frac{1}{\sqrt{{\mu }_o{\epsilon }_o}}$

C = speed in vacuum (symbol for velocity of EM waves)

${\mu }_o$ = Permacability in free space

${\epsilon }_o$ = Permittivity in free space

When air to water both ${\mu }_o$ and ${\epsilon }_o$ increases and value of C decreases.