STD 8 - SCIENCE: Light Worksheet with Questions on Mirrors, Reflection, and Refraction.

Here is the complete solution to the worksheet, with explanations for each answer.

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I. CHOOSE THE BEST ANSWER

1. __________ are used in vehicles as rear-view mirrors.
* Answer: b. convex mirrors
* Explanation: Convex mirrors curve outward. This shape gives them a wide field of view, allowing drivers to see more of the area behind and to the sides of the vehicle. Although the images formed are smaller and virtual, the increased视野 (field of view) is crucial for safety when changing lanes or reversing.

2. If the angle of incident is 30°, then the angle of reflection is __________
* Answer: c. 30°
* Explanation: According to the Law of Reflection, the angle of incidence (the angle between the incoming ray and the normal/perpendicular to the surface) is always equal to the angle of reflection (the angle between the reflected ray and the normal). So, if the incident angle is 30°, the reflected angle is also 30°.

3. ENT doctors use __________
* Answer: a. concave mirrors
* Explanation: ENT (Ear, Nose, and Throat) doctors use head mirrors, which are concave mirrors. These mirrors can focus light onto a specific area (like the ear canal or throat) by reflecting and converging the light from a lamp. The concave shape helps gather and direct the light precisely where needed for examination.

4. The formation of rainbow is an example of __________ of white light.
* Answer: d. dispersion
* Explanation: A rainbow is formed when sunlight passes through raindrops. The raindrops act like tiny prisms, bending (refracting) the light and separating it into its component colors (red, orange, yellow, green, blue, indigo, violet). This separation of white light into its constituent colors is called dispersion.

5. This picture resembles __________
*(The image shows parallel rays hitting a rough surface and scattering in different directions.)*
* Answer: c. irregular reflection
* Explanation: Irregular reflection (also called diffuse reflection) occurs when light hits a rough or uneven surface. Instead of reflecting at a single angle like on a smooth mirror (regular reflection), the light scatters in many different directions. The diagram clearly depicts this scattering effect.

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II. MATCH THE FOLLOWING

6. Snell’s law → e. Refraction
* Explanation: Snell's Law describes how light bends (refracts) when it passes from one medium into another with a different optical density. It mathematically relates the angles of incidence and refraction to the refractive indices of the two media.

7. Speed of light in vacuum → c. 3 x 10⁸ m/s
* Explanation: The speed of light in a vacuum is a fundamental physical constant, approximately 300,000,000 meters per second, or 3 × 10⁸ m/s.

8. Real image → a. Inverted
* Explanation: A real image is formed when light rays actually converge at a point. Real images are always inverted (upside down) relative to the object. They can be projected onto a screen.

9. Virtual image → b. Erect
* Explanation: A virtual image is formed when light rays appear to diverge from a point but do not actually meet there. Virtual images are always erect (upright) relative to the object. They cannot be projected onto a screen (e.g., your image in a plane mirror).

10. Refractive index of water → d. 1.33
* Explanation: The refractive index measures how much light slows down in a medium compared to a vacuum. For water, this value is approximately 1.33. This means light travels about 1.33 times slower in water than in a vacuum.

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Final Answer Key:

I.
1. b
2. c
3. a
4. d
5. c

II.
6. e
7. c
8. a
9. b
10. d