Flint Glass: A Higher-Index Prism

1 · Predict

Dense flint glass has a higher refractive index (n ≈ 1.66) than ordinary crown glass (n ≈ 1.5). Does a higher-index prism deviate light more or less than a lower-index one, at the same incidence angle and apex?

• More — a higher index bends light more strongly at each face, producing greater total deviation.
• Less deviation for a higher index.
• The deviation is unaffected by index.

2 · Set Up

1. Open the flint-prism preset and press Reset. This flint-glass prism has apex angle A = 60°, index n = 1.66.
2. Enable the total-deviation readout.
3. Set the incidence angle for each trial and record the total deviation.

3 · Collect Data

Plot deviation δ (y-axis) against incidence angle θ₁ (x-axis) for your three trials. Compare the overall scale to the white-light-prism experiment's crown-glass values.

4 · Analyze

1. For one trial, compute θ₂ = asin(sin θ₁/n), θ₃ = A − θ₂, θ₄ = asin(n·sin θ₃), then δ = θ₁ + θ₄ − A, using n = 1.66. Compare to the table.
2. Compare your deviation values here to the white-light-prism experiment's (same apex angle, lower index). Explain why flint glass's higher index produces consistently larger deviation at the same incidence angles.

5 · Extend

1. Camera lens designers combine crown-glass and flint-glass elements (an 'achromatic doublet') to cancel out chromatic aberration — since the two glass types disperse color differently. Explain why using only one type of glass, however precisely shaped, can't eliminate color fringing on its own.
2. Flint glass spreads a wider range of colors than crown glass for the same apex angle (more dispersion, not just more deviation). Explain why higher-index glasses like flint tend to disperse light more strongly across the visible spectrum.

The Physics Behind This Experiment

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