All questions of Light for Class 8 Exam

Hypermetropia cause long-sightedness which made a blurr image of nearby objects.

Correct answer is option 'D' 25 cm

A normal eye is unable to clearly see the objects placed closer than 25 cm because the ciliary muscles of eyes are unable to contract beyond a certain limit.

Virtual Image:
Virtual images are the images that cannot be captured on a screen or a photographic film. These images can only be seen by the eye and are produced by the apparent intersection of light rays. Here is an explanation of why virtual images cannot be captured on a screen:

Nature of Virtual Images:
- Virtual images are formed when light rays appear to diverge from a point behind the mirror or lens.
- These images are not real but appear to be located at a position where the light rays appear to meet or diverge from.

Cannot be Captured on Screen:
- Since virtual images are formed due to the apparent intersection of light rays, they do not actually converge at a physical point.
- Therefore, they cannot be projected onto a screen or captured on a photographic film because there are no actual light rays converging at the image location.

Contrast with Real Images:
- Real images, on the other hand, are formed by the actual convergence of light rays and can be captured on a screen or photographic film.
- Real images are formed in front of the mirror or lens and can be projected onto a screen to form a visible image.
In conclusion, virtual images are those that can only be seen by the eye due to the apparent intersection of light rays but cannot be captured on a screen or photographic film.

**Diffused Reflection**

Diffused reflection is a type of reflection that occurs when a ray of light strikes a rough or irregular surface and reflects in many different directions. It is also known as scattered reflection. Unlike regular reflection, where the light rays bounce off a smooth surface at the same angle, diffused reflection causes the light rays to scatter in various directions.

**Explanation**

Diffused reflection occurs on a rough surface because the irregularities on the surface cause the light rays to bounce off in different directions. These irregularities can be in the form of bumps, scratches, or any other roughness on the surface. When a ray of light strikes the surface, it interacts with these irregularities and gets scattered in many different directions.

**Comparison with Other Options**

a) Concave Mirror: A concave mirror is a curved mirror with a reflective surface that curves inward. It is commonly used in reflecting telescopes and makeup mirrors. When a ray of light strikes a concave mirror, it follows the law of reflection and bounces off at an angle equal to the angle of incidence. This is not diffused reflection but rather regular reflection.

b) Convex Mirror: A convex mirror is a curved mirror with a reflective surface that curves outward. It is commonly used in rear-view mirrors and security mirrors. Similar to a concave mirror, when a ray of light strikes a convex mirror, it follows the law of reflection and bounces off at an angle equal to the angle of incidence. Again, this is not diffused reflection but regular reflection.

c) Plane Mirror: A plane mirror is a flat mirror with a reflective surface. It is commonly used in bathrooms, dressing rooms, and for decorative purposes. When a ray of light strikes a plane mirror, it follows the law of reflection and bounces off at an angle equal to the angle of incidence. Just like concave and convex mirrors, this is regular reflection and not diffused reflection.

d) Rough Surface: A rough surface, as mentioned earlier, contains irregularities that cause light to scatter in different directions. When a ray of light strikes a rough surface, it interacts with these irregularities and gets reflected in multiple directions. This is diffused reflection.

Therefore, the correct answer is option 'D' - rough surface.

On the retina a real and inverted image is formed. Remember that real and inverted image can be obtain on the screen which is retina. But our brain interprets it erect and correct size. Or else we would see the whole things around us like upside-down

Given:
The distance between the mirror and the man's image = 4m
The man moves 1m towards the mirror

To find:
The new distance between the man and his image

Solution:
When an object is placed in front of a mirror, the image is formed at a distance equal to the distance between the object and the mirror. This distance is called the object distance.

In this case, the object distance is given as 4m.

Now, when the man moves towards the mirror by 1m, the new object distance becomes 4m - 1m = 3m.

Since the image distance is equal to the object distance, the new distance between the man and his image is also 3m.

Therefore, the correct answer is option A) 6m.

Summary:
When the man moves 1m towards the mirror, the distance between him and his image reduces by 1m. So, if the initial distance between the mirror and the man's image is 4m, the new distance will be 4m - 1m = 3m. Hence, the correct answer is option A) 6m.

Explanation:

Definition of a Light Year:
A light year is the distance that light travels in one year. Light travels at a speed of approximately 300,000 kilometers per second.

Calculation:
To calculate the distance covered by light in one year, we need to multiply the speed of light by the number of seconds in a year.
Speed of light = 300,000 km/s
Number of seconds in a year = 365 days * 24 hours * 60 minutes * 60 seconds = 31,536,000 seconds
Distance covered in one year = 300,000 km/s * 31,536,000 s = 9.5 x 10^12 km
Therefore, the correct answer is option C, which is 9.5 x 10^12 km.

Convex Lens as a Magnifying Glass
To understand at what position of the object a convex lens acts as a magnifying glass, we need to consider the characteristics of the lens and the image formation by it.

Image Formation by a Convex Lens:
- A convex lens forms an image of an object placed in front of it.
- The image can be real or virtual, upright or inverted, and magnified or diminished depending on the position of the object relative to the lens.

Focal Points of a Convex Lens:
- A convex lens has two focal points - F (the first focal point) and 2F (the second focal point) on its principal axis.

Position for Magnification:
- When the object is placed between the focal point (F) and the optical center (O) of the convex lens, the lens acts as a magnifying glass.
- In this position, the lens creates a virtual, erect, and magnified image of the object.
- The magnification is greater when the object is placed closer to the lens beyond F.
Therefore, the correct position of the object for a convex lens to act as a magnifying glass is between F and O.

Image formed by a plane mirror can never be real and enlarged, So Option (c) is the correct option

Because
let us take "n" as no of images
so to find this a formal is there
360/tetha -1
ex:- the image is formed at 60degree.. so find how many images are formed??
Ans》n= 360/60= 6 images are formed

Understanding the Eye's Components
The eye is a complex organ with several components that work together to facilitate vision. Among these, the iris plays a crucial role in regulating light entry.
What is the Iris?
- The iris is the colored part of the eye, located between the cornea and the lens.
- It consists of muscle fibers that can contract or relax.
Role of the Iris in Light Regulation
- The primary function of the iris is to control the size of the pupil.
- When exposed to bright light, the iris muscles contract, causing the pupil to become smaller (constricted). This reduces the amount of light that enters the eye, protecting the retina from excessive brightness.
- In low light conditions, the iris relaxes, allowing the pupil to dilate (enlarge) and increase light intake for better visibility.
Other Components of the Eye
- Pupil: The opening in the center of the iris; it is not a muscle and cannot adjust light levels on its own.
- Cornea: The transparent front layer of the eye that helps focus light but does not regulate light entry.
- Ciliary Muscles: These muscles control the shape of the lens for focusing but do not directly affect light levels entering the eye.
Conclusion
The iris is the key component that regulates the amount of light entering the eye by controlling the size of the pupil. Its ability to adjust in response to lighting conditions is essential for optimal vision, making it the correct answer to the question.

Understanding Mirror Images
When you look into a plane mirror, the image you see is a reflection of yourself. This reflection has certain properties that can be confusing, especially when it comes to lateral inversion.
Lateral Inversion Explained
- When you move your right hand or scratch your right cheek, the image in the mirror shows the opposite side.
- This phenomenon is known as lateral inversion, where left and right are swapped.
Applying Lateral Inversion to the Scenario
- If you scratch your right cheek, the image in the mirror will appear to scratch the opposite side, which is your left cheek.
- This is because the mirror reverses the image, making your right side appear as the left side in the reflection.
Conclusion
- Thus, if you are standing in front of a plane mirror and you scratch your right cheek, your image will indeed scratch its left cheek.
- This is why the correct answer is option 'B', demonstrating the concept of lateral inversion in mirrors effectively.

Time taken for light to reach from the earth to the sun
Light travels at a speed of approximately 299,792 kilometers per second (or about 186,282 miles per second). The distance from the Earth to the Sun is about 93 million miles (or 150 million kilometers).
To calculate the time taken for light to travel from the Earth to the Sun, we can use the formula:
Time = Distance / Speed

Calculation
- Distance from Earth to Sun: 93 million miles (150 million kilometers)
- Speed of light: 186,282 miles per second (299,792 kilometers per second)
Using the formula, we can calculate the time taken for light to reach from the Earth to the Sun:
Time = 93 million miles / 186,282 miles per second
Time = 499.11 seconds
Converting seconds to minutes:
Time = 499.11 seconds / 60 seconds per minute
Time ≈ 8.3 minutes
Therefore, it takes approximately 8.3 minutes for light to travel from the Earth to the Sun.
This explains why option 'B' (8.3 minutes) is the correct answer.

Dispenser

Option D is the right answer.
The person suffering from myopia can see nearly object clear but cannot see afar kept object clearly. So for correcting this doctor preferred a diverging lens and that is the concave lenses.

**Answer:**

When two plane mirrors are kept parallel to each other, they form multiple images of an object placed between them. The number of images formed depends on the angle between the mirrors and the position of the object.

Given, distance between the mirrors = 600 cm

To find the number of images formed, we can use the formula:

Number of images = (360°/angle between the mirrors) - 1

where angle between the mirrors = 360°/n where n is an integer representing the number of images formed.

Now, let's calculate the angle between the mirrors:

angle between mirrors = 360°/n = 360°/2 = 180°

Therefore, the angle between the mirrors is 180°.

Substituting this value in the formula, we get:

Number of images = (360°/180°) - 1 = 2 - 1 = 1

Thus, we can conclude that when two plane mirrors are kept 600 cm apart, only one image of an object placed between them is formed.

However, if the object is placed at a certain distance from the mirrors, multiple images can be formed due to the reflection of light rays. The number of images formed in such cases can be calculated using the same formula mentioned above.

For example, if the object is placed at a distance of 200 cm from one of the mirrors, three images will be formed. If it is placed at a distance of 150 cm from one of the mirrors, five images will be formed.

In the given options, option B (5) is the correct answer if the object is placed at a distance of 200 cm from one of the mirrors. If the object is placed at a different distance, the number of images formed will be different.