Question

Light travels with a speed of $2\times 10^{8}m/s$ in crown glass of refractive index $1.5$. What is the speed of light in dense flint glass of refractive index $1.8?$

• A. $1.33\times 10^{8}m/s$
• B. $67\times 10^{8}m/s$
• C. $2.0\times 10^{8}m/s$
• D. $3.0\times 10^{8}m/s$

Answer 1

Answer: (B)

$\mu =\frac{c}{v}$
$\therefore \frac{\mu }{{\mu }^{{}^{\prime }}}=\frac{v^{{}^{\prime }}}{v}$
$\frac{1.5}{1.8}=\frac{v^{{}^{\prime }}}{2\times 10^8}$
$v^{{}^{\prime }}=\frac{3\times 10^8}{1.8}$
$=1.67\times 10^{8}m/s$