The angle of deviation produced by a thin prism when placed in air is $\delta_1$ and that when immersed in water is $\delta_2$. The refractive indices of glass and water are $\frac{3}{2}$ and $\frac{4}{3}$ respectively. The ratio $\delta_1 : \delta_2$ is
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Physics Tip : When a prism is immersed in a liquid, the relative refractive index decreases, which in turn reduces the angle of deviation.