CBSE · Class 10 · Science · Light – Reflection and RefractionState the laws of refraction of light. Also, define refractive index of a medium and write its relation with the speed of light in vacuum. A ray of light enters from air to a glass plate having a refractive index of 1.5. What is the speed of light in the glass? (Speed of light in vacuum is $3 \times 10^8 \text{ m/s}$)

Laws of Refraction of Light

\nRefraction is the phenomenon of bending of light when it passes obliquely from one transparent medium to another. The laws governing the refraction of light are:

1. First Law: The incident ray, the refracted ray, and the normal to the interface of two transparent media at the point of incidence, all lie in the same plane.
2. Second Law (Snell's Law): The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant, for the light of a given color and for the given pair of media. $$\frac{\sin i}{\sin r} = \text{constant} (n_{21})$$\nThis constant value is called the refractive index of the second medium with respect to the first.

Refractive Index

\nThe refractive index of a medium measures how much the light slows down and bends when it enters that medium from a reference medium, usually vacuum or air. It is defined as the ratio of the speed of light in vacuum ($c$) to the speed of light in that medium ($v$): $$n = \frac{c}{v}$|

Numerical Problem Solution

Given Data:

• Refractive index of glass ($n$) = $1.5$
• Speed of light in vacuum ($c$) = $3 \times 10^8 \text{ m/s}$
• Speed of light in glass ($v$) = ?

Formula: $$n = \frac{c}{v}$$

Step-by-Step Calculation:

1. Rearrange the formula to solve for $v$: $$v = \frac{c}{n}$$
2. Substitute the given values into the equation: $$v = \frac{3 \times 10^8 \text{ m/s}}{1.5}$|
3. Perform the division: $$v = 2 \times 10^8 \text{ m/s}$|

Answer:\nThe speed of light in the glass plate is $2 \times 10^8 \text{ m/s}$.