Chapter-16 Light Question Answer

Explanation:

When there is no light in a room, it is impossible for a person to see objects inside the room. However, objects outside the room can still be visible if there is light present.

This is because for an object to be seen, light must reflect off it and enter the eye. In a dark room, there is no light for the object inside the room to reflect, making it impossible to see. On the other hand, objects outside the room may still be visible if there is light present, as the light can reflect off the object and enter the eye, allowing it to be seen.

Explanation:

Regular reflection occurs when light rays strike a smooth surface and are reflected in a single direction, producing a clear and sharp image. Examples of regular reflection include a mirror or still water surface.

Diffused reflection, on the other hand, occurs when light rays strike an uneven or rough surface and are reflected in many different directions, scattering the light and producing a blurred image. Examples of diffused reflection include a piece of paper, a wall, or a rough surface.

Diffused reflection does not mean the failure of the laws of reflection. The laws of reflection still hold true for diffused reflection, but the reflection is not as clear and sharp as in regular reflection. Instead, the light rays are scattered and reflected in multiple directions due to the uneven surface, resulting in a diffused or scattered reflection.

Explanation:

(a) Polished wooden table: Regular reflection will take place as a polished wooden table has a smooth surface, which reflects light in a single direction, producing a clear and sharp image.

(b) Chalk powder: Diffused reflection will take place as chalk powder has an uneven or rough surface, which reflects light in many different directions, producing a blurred or scattered image.

(c) Cardboard surface: Diffused reflection will take place as cardboard has an uneven or rough surface, which reflects light in many different directions, producing a blurred or scattered image.

(d) Marble floor with water spread over it: Diffused reflection will take place as the water on the marble floor creates an uneven or rough surface, which reflects light in many different directions, producing a blurred or scattered image.

(e) Mirror: Regular reflection will take place as a mirror has a smooth surface, which reflects light in a single direction, producing a clear and sharp image.

(f) Piece of paper: Diffused reflection will take place as a piece of paper has an uneven or rough surface, which reflects light in many different directions, producing a blurred or scattered image.

Explanation:

The two laws of reflection are:

The angle of incidence is equal to the angle of reflection: This means that the angle at which the incoming light strikes a smooth surface (the angle of incidence) is equal to the angle at which the light is reflected (the angle of reflection). This law holds true for all smooth surfaces, whether they are flat, curved or angled.

The incident ray, the reflected ray, and the normal to the surface all lie in the same plane: This means that the incident light, the reflected light, and the imaginary line drawn perpendicular to the surface (the normal) all lie in the same plane. The plane of incidence is the plane formed by the incident ray and the normal.

Explanation:

To perform this experiment, place a plane mirror on a table such that it is perpendicular to the table. Create a small hole in a piece of paper and hold it perpendicular to the table. It is best to perform this experiment in a dark room. Place another piece of paper on the table so that it makes contact with the mirror. Draw a line perpendicular to the mirror on the piece of paper on the table. Using a torch, beam light rays through the small hole such that the light hits the normal at the bottom of the mirror. The light ray will be reflected, and the reflected ray will be in the same plane as the incident ray and the normal line at the point of incidence on the mirror. This can be easily demonstrated by observing the reflected light on the piece of paper on the table.

Explanation:

(a) A person 1 m in front of a plane mirror seems to be 2 m away from his image.

According to the laws of reflection, the distance of the image from the plane mirror is the same as the distance of the object from the mirror. Since the person is 1 meter away from the mirror, the imag(e will appear to be 1 meter behind the mirror. Therefore, the total distance between the person and his image is 1 + 1 = 2 meters.

(b) If you touch your left ear with your right hand in front of a plane mirror, it will be seen in the mirror that your right ear is touched with your left hand.

When you stand in front of a plane mirror, your left side appears to be on the right side of your image, and your right side appears to be on the left side of your image. This is because the mirror reverses the left-right orientation of the image.

(c) The size of the pupil becomes larger when you see in dim light.

In dim light conditions, the amount of available light is limited, and so the pupil dilates (expands) to allow more light to enter the eye. This allows the eye to gather as much available light as possible, which can improve the ability to see in dim light. In bright light conditions, the opposite occurs, and the pupil constricts (shrinks) to reduce the amount of light entering the eye and protect it from potential damage.

(d) Night birds have fewer cones than rods in their eyes.

Rods are photoreceptor cells in the eye that are sensitive to low levels of light, but they are not very good at distinguishing colors. Cones, on the other hand, require more light and are better at color vision. Night birds, therefore, have a greater number of rods than cones, which helps them see better in dim light conditions.

Explanation:

The correct answer is (a) Always.

According to the laws of reflection, the angle of incidence is always equal to the angle of reflection, when light is reflected from a smooth and plane surface. This is true for all angles of incidence, and the relationship holds regardless of the properties of the reflecting surface or the properties of the incident light.

Explanation:

The correct answer is (b) virtual, behind the mirror and of the same size as the object.

When an object is placed in front of a plane mirror, a virtual image is formed behind the mirror. The image is called "virtual" because it cannot be projected onto a screen and "behind the mirror" because the light rays appear to be coming from behind the mirror. The image is also of the same size as the object, meaning it is neither enlarged nor reduced in size.

Explanation:

A kaleidoscope is a tube-shaped optical instrument that is used to create colorful and symmetrical patterns. The basic construction of a kaleidoscope involves a tube, a viewing end, a reflective surface, and small objects or particles.

Here are the steps to construct a simple kaleidoscope:

1. Take a cardboard tube or a PVC pipe of around 20-25 cm length and 3-4 cm diameter.

2. Cover one end of the tube with a transparent plastic sheet.

3. Fix three mirrors on the inner surface of the tube, making an angle of 60 degrees between them. The mirrors should be long enough to touch each other at one end and form a triangular prism.

4. At the other end of the tube, place a cardboard disc with a hole in the center, and secure it with tape or glue.

5. Fill the tube with small colorful objects like beads, buttons, or glass pieces.

6. Close the open end of the tube with another cardboard disc, making sure that it fits tightly.

7. Your kaleidoscope is now ready to use. Hold it up to the light and turn it slowly to see the colorful and symmetrical patterns formed by the reflections of the objects inside.

Explanation:

Explanation:

Gurmit was cautioned by her teacher against doing so due to the high intensity of the laser light, which can be dangerous to human eyes. Direct exposure to the beam can cause damage to the retina, leading to blindness. Therefore, it is recommended that one avoid looking at laser beams directly.

Explanation:

a) Avoiding reading in dim light as it can cause harm to the eyes.

b) If you work on a computer or do a lot of reading, take breaks every 20 minutes to rest your eyes and reduce eye strain.

c) Never rub your eyes if dust particles or an insect enters your eye instead rinse your eyes with water immediately.

d) Avoid exposure of eyes to direct sunlight.

e) Regular eye exams can help detect eye problems early and prevent vision loss. Adults should have their eyes checked every 2 years or as recommended by their eye doctor.

Explanation:

If the reflected ray is at an angle of 90° to the incident ray, it means that the angle of incidence is 45° (half of 90°). This is because the angle of incidence and the angle of reflection are always equal, and the sum of these two angles is 90° when the reflected ray is perpendicular (at a 90° angle) to the incident ray. Therefore, if the reflected ray is at a 90° angle to the incident ray, it must have been reflected at an angle of 45° from the surface.

Explanation:

If a candle is placed between two parallel plane mirrors separated by a distance of 40 cm, an infinite number of images of the candle will be formed.

Each mirror will reflect the candle image back and forth to the other mirror, and each reflection will produce a new image of the candle, resulting in an infinite number of images.

Explanation:

The path of reflected light can be determined using the first law of reflection.

It can be seen that the given ray of light will reflect from the second mirror at an angle of 60°.

When the incident ray OA reflects at point O, the angle of incidence equals the angle of reflection. Drawing a normal at O’, the two normals intersect at a 90° angle. The reflected ray OO’ makes an angle of 30° with the normal of the first mirror. Applying the angle sum property in triangle OXO’, we find that the angle of incidence in the second mirror is 60°. By applying the law of reflection in the second mirror, we obtain the figure shown below.

O’B is the reflected ray at 60°from the second mirror.

Explanation:

Boojho is unable to see his own image in the mirror as the reflected ray does not reach his eyes. However, he can see the images of objects located at P and Q as the rays of light emitted from those objects get reflected by the mirror and reach his eyes. On the other hand, Boojho cannot see the image of an object situated at R because the ray of light emitted from that object does not get reflected by the mirror and thus cannot reach his eyes.

Explanation:

a) An image of the object placed at point A is formed behind the mirror, and the distance of the image from the mirror is equal to the distance of the mirror from point A.

b) Yes, Paheli located at point B can see this image formed behind the mirror.

c) Similarly, Boojho located at point C can also see the same image formed behind the mirror.

d) The image of the object at point A will remain fixed in the same position even if Paheli moves from point B to point C.