Question

A type of glass block has a refractive index of 1.8.

1. Calculate the speed of light in this glass.
   (Given speed of light in air 3 ×10⁸ ms⁻¹)

2. If the width of this block is doubled, then what will be the speed of light in the block?

Answer 1

a. Given: Refractive index of the glass block = 1.8

Speed of light in air = 3 ×10⁸ ms⁻¹

As the refractive index (μ) of the glass block is given by,

μ = `"Speed of light in vacuum or air​"/"Speed of light in the glass block"`

⇒ Speed of light in the glass block = `"Speed of light in vacuum or air​"/mu`

= `(3 xx 10^8)/1.8`

= `(30 xx 10^8)/18`

= `(5 xx 10^8)/3`

≈ 1.67 × 10⁸ m s⁻¹

Hence, the speed of light in the glass block is approximately 1.67 × 10⁸ m s⁻¹.

b. Doubling the width of the glass block does not change the speed of light, as the speed of light in a medium is determined only by the refractive index of the material, independent of its thickness or width.