Refraction in a glass block: diagram showing light ray entering and bending within the glass block.

Problem Description:

The task involves understanding and labeling the refraction of light as it passes through a glass block. The diagram shows a beam of light entering a glass block at an angle, and we need to identify and mark the angle of incidence and the angle of refraction.

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Solution Explanation:

#### Step 1: Understanding Key Terms
1. Angle of Incidence (i):
- This is the angle between the incident ray (the incoming light ray) and the normal at the point where the light enters the glass block.
- The normal is a line drawn perpendicular to the surface of the glass block at the point of incidence.

2. Angle of Refraction (r):
- This is the angle between the refracted ray (the light ray after it enters the glass block) and the normal at the same point of incidence.

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#### Step 2: Identifying the Normal
- In the diagram, the normal is already drawn as a dashed line perpendicular to the surface of the glass block at the point where the light ray enters.

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#### Step 3: Marking the Angle of Incidence
- The angle of incidence is measured between the incident ray (the orange line before it enters the glass block) and the normal.
- Use a protractor or estimate the angle if a protractor is not available. Label this angle as \( i \).

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#### Step 4: Marking the Angle of Refraction
- The angle of refraction is measured between the refracted ray (the orange line inside the glass block) and the normal.
- Again, use a protractor or estimate the angle. Label this angle as \( r \).

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#### Step 5: Observing Snell's Law
- According to Snell's Law, the relationship between the angles of incidence and refraction is given by:
\[
n_1 \sin(i) = n_2 \sin(r)
\]
where \( n_1 \) is the refractive index of the medium outside the glass block (air, typically \( n_1 = 1 \)), and \( n_2 \) is the refractive index of the glass block (typically \( n_2 \approx 1.5 \)).
- Since light travels slower in glass than in air, the refracted ray bends toward the normal inside the glass block. This means the angle of refraction \( r \) is smaller than the angle of incidence \( i \).

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#### Final Diagram Labels:
1. Mark the angle of incidence (\( i \)) between the incident ray and the normal.
2. Mark the angle of refraction (\( r \)) between the refracted ray and the normal.

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Final Answer:

\[
\boxed{\text{Label the angle of incidence as } i \text{ and the angle of refraction as } r.}
\]

This completes the task of identifying and marking the angles of incidence and refraction in the diagram.