Determine the slope (m).

The calculation for the slope is provided in the image.

The slope is $\boxed{\text{0.533}}$.

Using the given formula $\eta_e = \frac{1}{m}$:

The value of $\eta_e$ is $\boxed{\text{1.875}}$.

$\eta_e$ represents the refractive index of the medium. It is a dimensionless quantity that indicates how much the speed of light is reduced when passing through the medium compared to its speed in a vacuum. A higher refractive index means light travels slower and bends more when entering the medium.

• Ensure the pins are vertical to accurately mark the light path.
• Use a clean glass block free from smudges or scratches to prevent light distortion.
• Draw thin, sharp lines for the incident ray, refracted ray, and normal to minimize measurement errors.
• Avoid parallax error when reading angles from the protractor by viewing directly perpendicular to the scale.
• Ensure the normal line is drawn accurately at the point of incidence, perpendicular to the surface.