Olympiad Test: Light, Shadows & Reflections - Class 6 MCQ

The image given in the question is of a periscope. It uses plane mirrors and multiple reflection to see the image. It is used in submarines.

The image formed by a plane mirror is always virtual, upright and of the same shape and size as the object it is reflecting. The image of object 'O' is seen at the same distance from the mirror as the distance between the object and the mirror. Therefore, the image appears to be at position 'b' after first reflection and on second reflection for the person it appears to be at 'd'.

A translucent object allows some light to pass through it, but not enough to see the full details or clear image of the source. When Abhishek looked at the lighted torch through the object, he could see a faint glow but not the torch itself. This suggests that the object is translucent, as it diffuses the light and prevents a clear image from being seen.

• A transparent object would allow the full image of the torch to be seen clearly.
• An opaque object would block all light, preventing any glow or image from being seen through

All of the provided statements explain why air is not visible:

• A: It is nearly a perfect transparent substance.
  Air is transparent, which means light passes through it without being absorbed or scattered significantly, making it invisible to the naked eye.
• C: It transmits whole of light.
  Air transmits light effectively, allowing the light to pass through without distorting or scattering it enough to make the air visible.
• D: It neither absorbs nor reflects light.
  Air does not absorb or reflect light in such a way that would make it visible. Instead, it allows light to pass through it, which is why we don’t see it.

Since all the statements are correct, B: All of these is the best answer.

When a person moves closer to a plane mirror, the size of their image in the mirror does not change. This phenomenon occurs because the size of the image in a plane mirror is always the same as the size of the object, regardless of the distance between the object and the mirror.

Therefore, the correct answer is: c) The size of image will be the same.

Book is an opaque object and hence does not allow the light of torch to pass through it. As there is no light on the ring, hence no image will be formed and the screen will remain dark due to absence of any light ray.

The glass does not form a dark shadow when light is shone on it because glass is a transparent object, allowing light to pass through it. Shadows are formed when an opaque object obstructs the path of light from a source. Glass, being transparent, allows light to pass through it without obstruction, hence preventing the formation of a shadow.

• A: The image formed by a pinhole camera is inverted because light travels in a straight line.
  This is true. In a pinhole camera, light travels in straight lines through the small hole (pinhole) and projects an inverted image on the opposite side of the box.

• B: Light does not change its direction on reflection.
  This is false. Light does change direction when it reflects off a surface, following the law of reflection (the angle of incidence equals the angle of reflection).

• C: As we move the object away from the light source, the shadow of the object becomes smaller.
  This is false. The shadow becomes larger as the object moves farther away from the light source, because the light rays diverge more.

• D: Reflection is possible only from unpolished surface.
  This is false. Reflection can occur on both polished and unpolished surfaces, but the type of reflection (specular or diffuse) depends on the smoothness of the surface. Polished surfaces cause specular reflection, which creates clear, sharp reflections.

Thus, the correct answer is A.

The umbra, the region of complete darkness is not able to reach the earth. The region of partial brightness, that is the penumbra.

Figure (iii) is periscope which is used to see around the corners. It is based upon the principle of rectilinear propagation of light and reflection of light. 

Note: Periscope is an optical instrument for viewing objects that are obstructed field of vision or above the level of direct sight.

To see the entire length of your body reflected in the mirror, you should use a mirror whose height will allow you to see your full image. 

A plane mirror is a mirror with a flat reflective surface. The image formed by a plane mirror is always virtual, upright and of the same shape and size as the object it is reflecting.

The ability to see the level of water in a cup depends on the transparency of the material.

• Glass cup: Glass is transparent, which means Vijay will be able to clearly see the level of water inside the glass cup.
• Steel cup: Steel is opaque, so Vijay will not be able to see through it.
• Porcelain cup: Porcelain is usually opaque or semi-translucent, so it will not allow clear visibility of the water level.
• Frosted glass cup: Frosted glass is translucent, meaning it diffuses light and partially blocks visibility, so Vijay will not see the water level as clearly as in a regular glass cup.

Thus, the correct answer is A: Glass cup.

• A metal plate: Metal is opaque, so it does not allow light to pass through.
• A glass tumbler: Glass is transparent, meaning it allows light to pass through easily.
• A book: A book is opaque, so it does not allow light to pass through.
• A wooden block: Wood is also opaque, preventing light from passing through.

Thus, the correct answer is B: A glass tumbler.

The length of the shadow of a stick depends on the position of the sun in the sky. At different times of the day, the angle of the sun changes, which in turn affects the length of the shadow.

• At 8:15 am, the sun is relatively low in the sky, creating a longer shadow.
• At 12:00 noon, the sun is at its highest point in the sky (in the case of most locations, it is directly overhead or near overhead). At this time, the shadow of the stick will be much shorter because the angle between the stick and the sun is very small.

So, the shadow at 12:00 noon will be shorter than the shadow at 8:15 am.

The correct answer is: (a) It will be shorter than one at 8:15 am.

All the rays that comes out from an object that kept at the centre of a transparent. Sphere will be normal to the surface of the sphere.

Transparent material allows light to pass through it and opaque object obstructs it. Translucent material allows some light to pass through it. In this case, bright spot is produced as the object is opaque. Shadows are formed when the opaque object is present.

Specular reflection occurs when parallel rays of light hit a smooth surface, and after reflection, the rays remain parallel to each other. This type of reflection results in clear, well-defined images (like in a mirror), because the reflective angles are all the same for each incident ray.

• Diffused reflection: This happens when light strikes a rough surface, scattering the rays in many directions, which results in a blurry or unclear image.
• Mirror reflection: This is essentially a form of specular reflection but specifically refers to the reflection from a mirror's smooth surface.
• Lake reflection: This is an example of specular reflection that occurs on the surface of water, but it is not a distinct type of reflection.

Thus, the correct answer is A: Specular reflection.

When light that has been reflected from an object enters our eyes, images are created. When the surface is smooth and bright, the entire light is reflected.When light striking an item reflects and reaches our eyes, we perceive the object. When a surface reflects the majority of the light falling on it, an image is created on it. The majority of pictures are created on smooth, reflective surfaces like mirrors and metal. When a glass is flawlessly polished with any colour, like red, it becomes smooth and bright, reflecting all of the light that strikes it.The light that fell on Riya and Priya was now mirrored in all directions as they were seated around a round table. The table receives the light that is reflected from them, and because of its polish, it returns all of that light. They may see each other's pictures on top of the table because the table's reflected light penetrates their eyes. Hence B is the correct answer.

A pinhole camera works by allowing light to pass through a tiny hole (the aperture) and project an image on the opposite side of the camera. It does not use a lens, but the small hole (aperture) serves to focus the image.

• B: Has a lens, but no aperture: This is incorrect, as a pinhole camera does not have a lens.
• C: Has no lens and no aperture: This is incorrect, as the pinhole serves as the aperture.
• D: Has a self-timer: This is incorrect, as a pinhole camera typically does not include such features.

Thus, the correct answer is A: Has an aperture, but no lens.

A coloured plastic bottle is an opaque material. When a light beam is incident on it, a shadow will form on the screen. Light can pass through the transparent sheet. 

The materials that allow only some of the light to pass through them are known as translucent materials. 

• A: A cylindrical object can cast a rectangular as well as a circular shadow.
  This is true. Depending on the angle of the light source and the orientation of the cylindrical object, it can cast both rectangular (if the object is viewed from the side) and circular (if viewed from the top) shadows.

• B: Polished surface produces a clear image.
  This is true. A polished surface causes specular reflection, which creates clear and sharp images, as it reflects light in parallel directions.

• C: The umbra is the region of a shadow which is grey in colour.
  This is false. The umbra is the darkest part of a shadow, where the light source is completely blocked. It is typically black or very dark, not grey. The penumbra is the lighter, greyish region of the shadow, where some, but not all, of the light is blocked.

• D: Light travels in a straight line.
  This is true. In the absence of obstacles or medium changes, light travels in a straight line.

Thus, the statement that is not true is C: The umbra is the region of a shadow which is grey in colour.