The refractive index of a transparent liquid is 1.25. If the speed of light in vacuum is \(3 \times 10^{8}\) m/s, what is the speed of light in this liquid?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → \(2.4 \times 10^{8}\) m/s
The refractive index of a medium is \(n = \frac{c}{v}\), where \(c\) is the speed of light in vacuum and \(v\) its speed in the medium. So \(v = \frac{c}{n}\).
\(c = 3 \times 10^{8}\,\mathrm{m/s}\); \(n = 1.25\)
\(v = \frac{3 \times 10^{8}}{1.25}\)
\(v = 2.4 \times 10^{8}\,\mathrm{m/s}\)
Light is slower in the liquid than in vacuum, as expected for a medium with \(n > 1\).