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Define refractive index

The refractive index of a medium is $n=c/v$ , where $c$ is the speed of light in vacuum and $v$ is its speed in the medium. A larger $n$ means a lower light speed in that medium.

Relate speed and wavelength

At a stationary boundary the frequency is unchanged. Since $v=f\lambda$ , a lower speed means a shorter wavelength. For two media, $n_2/n_1=\lambda_1/\lambda_2$ when the frequency is common.

Use a graph or measurement

If a graph’s gradient represents $n$ , state that interpretation before reading the value. For uncertainty, use the spread from suitable maximum and minimum lines or the specified uncertainty method.

Common trap

Do not use $n=v/c$ , and do not assume wavelength stays fixed when light enters a different medium. Frequency is the quantity that remains fixed at a stationary boundary.

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Determine the value of the refractive index of the glass with its absolute uncertainty.

C.3 Wave phenomena is secure when you can connect the physical picture to the equation and its limits.

Wavefronts and rays
Reflection, refraction and Snell’s law
Refractive index and total internal reflection
Superposition, coherent sources and interference
Young’s double-slit pattern

C.3.3—Refractive index

Calculate Refractive Index

Retrieve the Core C.3 Wave Phenomena Model

C.3.3 Exam Analysis