Solutions-NCERT-Class-8-Science-Curiosity-Chapter-10-Light: Mirrors and Lenses-CBSE

Yes, we can make mirrors that give enlarged or diminished images.

• Concave mirror: It can give an enlarged image when the object is placed close to the mirror (between the pole and focus). Example: shaving mirror, dentist’s mirror.
• Convex mirror: It always gives a diminished image of the object. Example: rear-view mirrors in vehicles.

So, by using concave and convex mirrors, we can get enlarged or diminished images.

The warning “Objects in mirror are closer than they appear” is written because side-view mirrors are convex mirrors.

• A convex mirror always forms a diminished (smaller) image of objects. Since the image looks smaller, our eyes judge the object to be farther away than it actually is. In reality, the object (vehicle) is closer than it appears in the mirror.

Therefore, this warning is given to prevent accidents and help drivers judge the correct distance of nearby vehicles.

The curved line seen on some reading glasses is because they are bifocal lenses.

These glasses have two different lens powers in one frame:

• The upper part is used for seeing distant objects.
• The lower part is used for reading or near objects.

The curved line separates these two parts and shows where the lens power changes. This helps people who have difficulty seeing both near and far objects clearly

We can distinguish between concave and convex mirrors by observing the type of image formed:

• Concave mirror: It can form a real and inverted image (on a screen) when the object is far away. It can also form a virtual and enlarged image when the object is very close.
• Convex mirror: It always forms a virtual, erect, and diminished image and cannot form a real image on a screen.

So, if a mirror can form a real image on a screen, it is a concave mirror; if it always gives a small, upright image, it is a convex mirror.

Yes, image formation by all types of mirrors (plane, concave, and convex) is governed by the laws of reflection.

There are two laws of reflection:

• The incident ray, the reflected ray, and the normal at the point of incidence all lie in the same plane.
• The angle of incidence is equal to the angle of reflection.

These two laws apply to plane mirrors as well as curved mirrors (concave and convex) and explain how images are formed by mirrors.

Yes, the laws of reflection are applicable to spherical mirrors also.

These laws state that the angle of incidence is equal to the angle of reflection, and the incident ray, reflected ray, and normal all lie in the same plane. These laws hold true for all types of reflecting surfaces, including spherical mirrors like concave and convex mirrors.

When objects are viewed through lenses, the following changes can be seen:

• Size of the object may change: it may appear enlarged or diminished.
• Position of the image may change: the image may appear nearer or farther than the object.
• Nature of the image may change: the image can be real or virtual.
• Orientation may change: the image can be erect or inverted (in some cases).

Thus, lenses can change how big an object looks, where it appears, and the type of image formed.

Yes, lenses can both converge and diverge light beams. Convex lenses converge (focus) light, while concave lenses diverge (spread out) light.

Yes, a convex lens can burn a paper.

• A convex lens converges parallel rays of sunlight to a small bright point called the focus. At this point, a large amount of heat energy is concentrated in a very small area. If a piece of paper is placed at the focus, it gets heated strongly and starts burning.

This happens because sunlight carries heat energy, and the convex lens concentrates this energy at one point.

Lenses are used in a variety of applications, both in everyday life and in scientific instruments. These include eyeglasses, cameras, microscopes, telescopes, and projectors, as well as simple magnifying glasses and spyholes in doors.

(ii) 50°

Explanation : The angle of incidence is given as 40° (measured with the normal).

According to the law of reflection:

Angle of reflection = Angle of incidence = 40° (with the normal)

The mirror surface is perpendicular to the normal, so:

Angle with mirror = 90⁰ - 40⁰ = 50⁰

Answer: The reflected ray makes an angle of 50° with the mirror.

(i) Light ray falls along the normal

Angle of incidence = 0°

Angle of reflection = 0°

The ray retraces its path. It reflects straight back along the same line.

(ii) Mirror is tilted, but light ray still falls along the normal to the tilted surface

Even though the mirror is tilted, the ray is still perpendicular to the surface.

Angle of incidence = 0°

Angle of reflection = 0°

The ray again retraces its path – the tilt doesn't affect the reflection if the ray is normal to the surface.

(iii) Mirror is tilted, and light ray falls at 20° from the normal

Angle of incidence = 20°

By the law of reflection:

Angle of reflection = 20°

The reflected ray will make a 20° angle with the normal, on the opposite side.

(ii) Angle of incidence is 0°

Explanation : When light hits a surface at a 90° angle (perpendicular), it is considered to be incident normally.

Angle of incidence = Angle of reflection:

In reflection, the angle of the reflected light is always equal to the angle of

the incident light. Since the light is hitting the mirror normally (at a 0° angle), the reflected light will also be at a 0° angle.

 (i) her erect image keeps decreasing in size.

Explanation : Convex mirror always forms virtual, erect and diminished image.

A magnifying glass produces a magnified, upright image when the object is placed inside its focal length. A magnifying glass is a convex lens.

Explanation :

• When you hold a magnifying glass close to the text (within a certain short distance), the letters appear bigger and clear.
• This happens when the text is placed within the focal length of the lens.
• Now, when you move the magnifying glass away from the text, the letters first become less clear, and after some distance they may appear inverted and smaller or blurred.

Correct matching is:

(i) Concave mirror - (a) Spherical mirror with a reflecting surface that curves inwards.

(ii) Convex mirror - (b) It forms an image which is always erect and diminished in size.

(iii) Convex lens - (c) Object placed behind it may appear inverted at some distance.

(iv) Concave lens - (d) Object placed behind it always appears diminished in size.

(i) Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.

(ii) Figure (a) indicates a convex mirror and Figure (b) indicates a concave mirror.

When we place a pencil behind a transparent glass tumbler and fill the tumbler

halfway with water, the pencil will appear to be bent or broken at the point where it

enters the water. The submerged portion of the pencil might also appear slightly thicker or shifted from its actual position.

This happens due to refraction of light. Light rays coming from the pencil change their direction when they pass from water to air through the glass. Because of this bending of light, the part of the pencil inside the water appears shifted from its actual position, making the pencil look bent or broken at the surface of the water.