he composition of the ancient atmosphere can be determined by analyzing bubbles of air trapped in amber, which is fossilized tree resin. (This is one way we know that the air in the time of the dinosaurs was richer in oxygen than our current atmosphere.) An air bubble appears to be 7.2 mm below the flat surface of a piece of amber, which has index of refraction 1.54. How long a needle is required to reach the bubble

the needle must be 11.1 mm long to reach the bubble

Explanation:

 Given that;

An air bubble appears to be 7.2 mm below the flat surface of a piece of amber

so Apparent depth = 7.2 mm

index of refraction = 1.54

we know that;

Refractive index = Real depth / Apparent depth

we substitute

1.54 = Real depth / 7.2 mm

Real depth = 1.54 × 7.2 mm

Real depth = 11.088 ≈ 11.1 mm

Therefore, the needle must be 11.1 mm long to reach the bubble