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Physics

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

(a) Calculate the speed of light in this glass. (Given speed of light in air 3 x 108 m s-1)

(b) If the width of this block is doubled, then what will be the speed of light in the block?

Refraction Plane Surfaces

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Answer

(a) Given,

  • Refractive index of the glass block = 1.8
  • Speed of light in air = 3 x 108 m s-1

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

μ=Speed of light in vacuum or airSpeed of light in the glass block⇒Speed of light in the glass block=Speed of light in vacuum or airμ=3×1081.8=30×10818=5×1083≈1.67×108 m s−1\text μ = \dfrac{\text {Speed of light in vacuum or air}}{\text {Speed of light in the glass block}} \\[1em] \Rightarrow \text {Speed of light in the glass block} = \dfrac{\text {Speed of light in vacuum or air}}{\text μ} \\[1em] = \dfrac{3\times 10^8}{1.8} \\[1em] = \dfrac{30\times 10^8}{18} \\[1em] = \dfrac{5\times 10^8}{3} \\[1em] \approx 1.67 \times 10^8 \text { m s}^{-1}

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

(b) If the width of the glass block is doubled, the speed of light does not change because the speed of light in a medium depends only on the refractive index of the material, not on its thickness or width.

Therefore, the speed remains 1.67 x 108 m s-1.

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