Exercises: Light | Class 7 Oxford Science: Chapter Notes, Worksheets & Tests PDF Download

 Objective Type Questions 

Rectilinear propagation of light means light travels in straight lines.'
The term 'rectilinear' refers to the property of traveling in straight lines. Therefore, the correct answer is 'straight lines'.

Q.2. A bumpy, rough surface is also referred to as a________ (diffused/irregular) surface. 

A bumpy, rough surface is also referred to as a diffused surface.
The term 'diffused' refers to the scattering of light in multiple directions due to a bumpy or rough surface. Therefore, the correct answer is 'diffused'.

Q.3. A convex mirror can only form _________(real/virtual) images.

A convex mirror can only form virtual images.
A convex mirror always forms virtual images, which are formed by the apparent intersection of reflected rays. Therefore, the correct answer is 'virtual'.

Q.4. A concave lens is a ________(diverging/converging) lens.

A concave lens is a diverging lens.
A concave lens is thinner at the center than at the edges and causes light rays to diverge. Therefore, the correct answer is 'diverging'.

Q.5. A virtual image ________(can/cannot) be formed on a screen. 

A virtual image cannot be formed on a screen.
A virtual image is formed when the rays of light do not actually converge at the position of the image. Since the rays do not actually converge, a virtual image cannot be formed on a screen. Therefore, the correct answer is 'cannot'.

B. Choose the correct option.

Very Short Answer Type Questions 

Concave mirror

Q.2. A lens that is thicker at the edges than at the middle _________

Convex lens

Q.3. An image that is upside down _________

Inverted image

Q.4. A band of colours that is formed when white light is passed through a prism _________

Spectrum

Q.5. The property of our eyes that makes us perceive a rotating coloured disc as white _________

Persistence of vision

Short Answer Type Questions 

a. ECNALUBMA

b. TFEL

c. 87654321

d. 8888 (looks the same in a plane mirror)

Q.2. If sunlight is streaming in through a window in a room, how could we make it fall on a wall which is on the same side as the window? 

We can use a mirror to reflect the sunlight towards the wall.

Q.3. How can we find out if an image formed (either by a mirror or a lens) is real or  virtual? 

An image is real if it can be projected on a screen. If it cannot be projected, it is virtual.

Q.4. Why are convex mirrors used as car wing mirrors?

Convex mirrors are used as car wing mirrors because they provide a wider field of view. They also make objects appear smaller, which allows the driver to see more of the surroundings.

Long Answer Type Questions 

The reflection from a regular surface is regular and follows the laws of reflection, i.e., the angle of incidence is equal to the angle of reflection and the incident ray, reflected ray and normal to the surface all lie in the same plane. On the other hand, the reflection from an irregular surface is irregular and does not follow the laws of reflection. The incident ray gets reflected in different directions and the reflected rays do not form a clear image.

Q.2. You are given a plane mirror, convex mirror, concave mirror, convex lens and a concave lens. Give two methods by which you can form diminished images of an object and two methods by which you can form enlarged images. 

To form a diminished image of an object:

a) Place the object in front of a convex lens and adjust the distance between the object and the lens until a sharp, small image is formed on the other side of the lens.

b) Place the object in front of a concave mirror and adjust the distance between the object and the mirror until a small, inverted image is formed behind the mirror.

To form an enlarged image of an object:

a) Place the object in front of a concave lens and adjust the distance between the object and the lens until a large, virtual image is formed on the same side of the lens as the object.

b) Place the object in front of a convex mirror and adjust the distance between the object and the mirror until a virtual, erect and magnified image is formed behind the mirror.

Q.3. What is a Newton's disc? What is it used to demonstrate? Explain how.

Newton's disc is a disc with different colors arranged in a circular pattern. It is used to demonstrate the phenomenon of white light consisting of all colors of the spectrum. When the disc is rotated at a high speed, the colors appear to merge together and form white light. This happens because the retina of our eyes cannot distinguish between different colors when they are moving rapidly. The disc shows that white light is actually a combination of different colors and that these colors can be separated using a prism.