A Level Physics Practice Exam

What is the refractive index (n) of a material defined by?

1. n = c / c1

2. n = c1 / c

3. n = c + c1

4. n = c - c1

The correct answer is: n = c / c1

The refractive index of a material is defined as the ratio of the speed of light in a vacuum (or air) to the speed of light in the material itself. In this context, \( c \) represents the speed of light in a vacuum, and \( c_1 \) represents the speed of light in the material. The correct expression for the refractive index is given by: \[ n = \frac{c}{c_1} \] This means that the refractive index quantifies how much the light slows down when it enters a material from a vacuum. A higher refractive index indicates that light travels more slowly in that material compared to a vacuum, while a lower refractive index indicates that light travels relatively faster. This definition directly aligns with the fundamental concepts of optics, where understanding how light interacts with different materials is crucial for applications in lenses, optical fibers, and various imaging systems. Other choices do not accurately represent the relationship defined by the refractive index.