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 × 108 m s−1)
(b) If the width of this block is doubled, then what will be the speed of light in the block?
(a) Given, refractive index of the glass block = 1.8 and speed of light in air = 3 × 108 m s−1.
Speed of light in glass = \frac{3\times10^8}{1.8} = 1.67 × 108 m s−1.
(b) If the width of the glass block is doubled, the speed of light does not change because it depends on the refractive index of the material, not its thickness.
Therefore, the speed remains 1.67 × 108 m s−1.
More ICSE Moderate level questions
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Copy the diagram given below and complete the path of the light ray PQ, as it emerges out of the prism by marking necessary angles. The critical angle of glass is 42°.
(a) Out of the three rays (I, J, H) shown in the diagram, which ray will suffer Total Internal Reflection while inside the prism? (Critical angle of the prism is 42°.) (b) Copy the diagram to complete the path of the ray which you have named in (a) till it comes out of the prism.
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