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A glass prism is immersed in a liquid. The refractive index n versus wavelength lambda curves for glass and liquid intersect at the yellow wavelength. When white light hits the prism parallel to its base, which statement is correct?

1. The yellow ray passes through without any deviation.
2. The blue ray is deflected toward the apex (vertex).
3. The red ray is deflected toward the base.
4. No dispersion occurs for any wavelength.

Correct answer: The yellow ray passes through without any deviation.

Solution

At the yellow wavelength the curves cross, meaning n_glass = n_liquid there, so the yellow ray experiences no refraction and passes through undeviated. For other wavelengths, n_glass != n_liquid and deviation occurs.

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