GRADE 8 SCIENCE - LIGHT REVISION WORKSHEET • Teacha! - Free Printable

Let's go through each part of your worksheet step by step and solve the problems with explanations.

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1. What are the 7 different colours we see when visible white light passes through a prism or water droplet?

When white light (which is a combination of all visible colors) passes through a prism or a water droplet, it undergoes dispersion — meaning it splits into its constituent colors due to different wavelengths bending at slightly different angles.

The seven colors in order (from longest to shortest wavelength) are:

1. Red
2. Orange
3. Yellow
4. Green
5. Blue
6. Indigo
7. Violet

> 🔹 Note: This sequence is often remembered using the mnemonic: "ROYGBIV" – Red, Orange, Yellow, Green, Blue, Indigo, Violet.

✔ So fill in:
1. Red
2. Orange
3. Yellow
4. Green
5. Blue
6. Indigo
7. Violet

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2. Label the diagram which represents reflected light. Identify the different rays and angles.

This diagram shows reflection off a mirror. The key components are:

- Incident ray: The incoming light ray before hitting the mirror.
- Reflected ray: The outgoing light ray after bouncing off the mirror.
- Normal: A line perpendicular to the surface at the point of incidence.
- Angle of incidence: The angle between the incident ray and the normal.
- Angle of reflection: The angle between the reflected ray and the normal.

According to the Law of Reflection:
> Angle of incidence = Angle of reflection

Labeling:

- Left side (incoming):
- Top box → Incident Ray
- Bottom box → Angle of Incidence

- Right side (outgoing):
- Top box → Reflected Ray
- Bottom box → Angle of Reflection

- The vertical line → Normal

✔ Final labels:
- Incident Ray
- Angle of Incidence
- Reflected Ray
- Angle of Reflection
- Normal (already labeled)

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3. Complete the diagram to show what happens when light hits the surface of glass.

Light travels from air (less dense) into glass (more dense). When this happens:

- The light refracts (bends) toward the normal because it slows down in the denser medium.
- Some light may also reflect back (partial reflection), but the main effect here is refraction.

You should draw:
1. An arrow showing the incident ray coming from air into glass.
2. A refracted ray inside the glass, bent toward the normal.
3. Optionally, a small reflected ray going back into the air (but usually not emphasized unless specified).

✔ Draw:
- A dashed line for the normal at the interface.
- The refracted ray bending toward the normal as it enters the glass.
- Label:
- Incident ray
- Refracted ray
- Normal
- Air / Glass boundary

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4. Explain what is happening in the picture to the right.

The image shows white light entering a prism, spreading out into a spectrum of colors.

➡️ Explanation:

White light is made up of many different colors, each with a different wavelength. When it enters the prism, it refracts (bends) because it moves from air to glass. Since each color has a different wavelength, they refract by different amounts — shorter wavelengths (like violet) bend more than longer ones (like red).

As the light exits the prism on the other side, it refracts again, further spreading the colors apart. This process is called dispersion.

➡️ Result: A rainbow-like spectrum of colors appears.

✔ Write:

> White light enters the prism and refracts (bends) as it passes from air into glass. Because each color of light has a different wavelength, they bend by different amounts. This causes the white light to split into its component colors — red, orange, yellow, green, blue, indigo, and violet — forming a spectrum. This phenomenon is called dispersion.

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5. Fill in the blanks: Light enters the eye through a hole called the ________ and when it reaches the ________ at the back of the eye, receptors are stimulated...

These are standard parts of the human eye:

- The hole that lets light in is the pupil.
- At the back of the eye, the light lands on the retina, which contains photoreceptor cells (rods and cones) that detect light and color.

✔ Fill in:
- First blank: pupil
- Second blank: retina

So:
> Light enters the eye through a hole called the pupil and when it reaches the retina at the back of the eye...

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✔ Summary of Answers:

#### 1. Colors of the Spectrum:
1. Red
2. Orange
3. Yellow
4. Green
5. Blue
6. Indigo
7. Violet

#### 2. Reflection Diagram Labels:
- Left:
- Incident Ray
- Angle of Incidence
- Right:
- Reflected Ray
- Angle of Reflection
- Vertical line: Normal (already labeled)

#### 3. Refraction Diagram:
- Draw refracted ray bending toward the normal upon entering glass.
- Label: Incident ray, Refracted ray, Normal, Air/Glass boundary.

#### 4. Explanation of Prism Diagram:
> White light enters the prism and bends due to refraction. Different colors bend by different amounts because they have different wavelengths, causing the light to separate into a spectrum of colors. This is known as dispersion.

#### 5. Eye Structure:
- Pupil
- Retina

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Let me know if you'd like a visual version of the diagrams or help drawing them!