DAV Class 7 Science Chapter 12 Light Question Answer Notes
DAV Class 7 Science Chapter 12 Light Question Answer Notes Solution by Expert Science Teacher. DAV Class 7 Science 12th Chapter Light for Students of DAV Schools.
Lesson No 12
Light
A.) Fill in the blanks.
Answer: (1) real (2) equals (3) normal, plane (4) focus (5) convex (6) concave
B.) Write True or False for the following statements.
Answer: (1) False, the image formed by a plane mirror is laterally inverted (2) True (3) False, a concave mirror forms a virtual image (4) Fals , only concave mirror can be used (5) True
C.) Tick the correct option.
Answer:
(1) normal at the point of incidence.
(2) just retraces the path.
(3) pole of the mirror.
(4) 4m
(5) 8m/s
D.) Answer the following questions in brief.
1.) Explain clearly the difference between a real image and a virtual image. Give one example of a virtual image.
Answer: When light is correctly positioned on a surface, a real image is created. It is a physical depiction of anything that could be photographed or shown on a screen. The closest thing to an actual picture there is is a photograph. An image that seems to be emanating from somewhere other than its true location is called a virtual image. It’s an optical illusion made by light beams rather than a precise physical representation of an object. A person’s reflection in a mirror is an illustration of a virtual image.
2.) How does changing the distance of the object, from a convex mirror, affect the size and nature of the image formed by it?
When an object is placed directly in front of a convex mirror, the size and kind of the image that is produced depends on the object’s proximity to the mirror. As the object is moved further from the convex mirror, the image gets smaller and appears to be farther away. When two items are very close to one another, a virtual, upright, and smaller-than-the-real-thing image is produced. As the object travels farther away from the mirror, the image becomes more virtual, upright, and diminished. The image is formed to be virtual, upright, and approximately the same dimension as the object when viewed from a particular distance.
3.) Draw a ray diagram to show the formation of an image when the object is placed between the C and F points of a concave mirror.
4.) Where should we keep an object, in front of a concave mirror, so as to get a virtual and magnified image of it?
By tracing a line from a mirror’s focus to its surface, one may determine the mirror’s centre of curvature. The major axis is the name of this line. After then, the centre of curvature is 2F distant from this line. The item must then be positioned in this manner in order to create both a virtual and expanded image. When the object is put farther away than the mirror’s focal length, a virtual picture is created. This image is magnified and seems to be behind a mirror. The image enlarges as the item gets closer to the mirror. As a result, it is necessary to position the object near to the mirror’s sphere’s centre.
5.) The magnified image, of an object, appears to be formed, behind the mirror, by an apparent intersection of the reflected rays. What can you say about (a) nature of the image (b) the type of mirror used?
Answer: (a) Virtual image (b) Concave mirror
6.) Rohit suggested to his father to fix a ‘security mirror’ which would provide them with a wider view of the surrounding of their shop. Name the type of mirror that Rohit must have suggested to his father. Also mention the basic characteristics of the image formed by this type of mirrors.
Answer: Rohit must have suggested using a convex mirror, also known as a “security mirror,” to his father. Convex mirrors are curved outward, rather than inward like concave mirrors.The basic characteristics of the image formed by a convex mirror are:
- The image is always smaller and gives the impression that the object is farther away.
- Since the image is virtual, it cannot be projected onto a screen.
- They are widely used in security applications because they provide a wider perspective of a region than the item they are reflecting. The image is also vertical.
Type of mirror used is a convex mirror.
7.) State the type of mirror that the following items/objects would correspond to:
(a) inside of a stainless-steel bowl
(b) reflector of a torch
(c) a polished shining wooden surface
(d) the shiny outer surface of the bicycle bell.
Answer:
(a) Concave mirror
(b) Concave mirror
(c) Plane mirror
(d) Convex mirror
E.) Answer the following questions.
1.) State the laws of reflection. Describe an activity to show that incident ray, reflected ray and the normal, at the point of incidence, all lie in the same plane.
Answer:
1.) The reflected ray, the incident ray, and the normal to the reflecting surface all lie in the same plane.
2.) The angle of incidence is equal to the angle of reflection.
3.) The incident ray, the reflected ray, and the normal all form a right angle.
For this practise, students will need a mirror as well as some paper. After laying the mirror down on a flat surface, arrange the paper on over of the mirror. Next one needs to trace a circle all around the edge of the mirror using a pencil. As soon we raise the paper up, the mirror tracing, we see that the incident ray’s path, as well as the normal all reside within the same plane.
3.) Draw a ray diagram to show the formation of the image of a point object by (i) a plane mirror and (ii) a convex mirror.
4.) Three persons are standing at points P, Q and R in front of a plane mirror. Can ‘P’ see himself in the mirror? Also, can he see the image of Q and R in the mirror?
Answer: No, P can’t see image of himself but he can see image of Q and R.
5.) With the help of a suitable diagram, explain the meaning of the following terms for a concave mirror.
(a) centre of curvature – The centre of curvature is the imaginary centre on middle of the sphere of which the convex or concave mirror is a part of.
(b) pole- It is said to be the geometrical centre of a mirror which is part of a sphere.
(c) principal axis- The principal axis is the straight line that joins the pole and the centre of curvature
(d) focus- It is a point on the principal axis at which incident rays parallel to the principal axis either meet or appear to meet upon reflection
6.) What type of mirror is used in the following cases? Is the image formed virtual and erect in each case?
(a) ‘make up’ mirror
(b) ‘rear view’ mirror of vehicles
(c) reflecting type telescope
(d) shaving mirror
Answer:
(a) Plane mirror
(b) Convex mirror
(c) Curved mirror
(d) Plane mirror
No, image is not virtual and erect in each case.
More Extra Questions for Preparation
Q.1.) Fill in the blanks.
1.) A ray, directed towards the centre of curvature of a spherical mirror, retraces its path after reflection.
2.) The minimum distance, between an object and its real image, formed by a concave mirror, is zero.
3.) A virtual image is formed by the apparent intersection of light rays.
4.) The ‘central point’ for the given spherical mirror is called pole.
5.) In concave lens the image is erect and smaller in size than the object.
Q.2.) Match the following.
1.) Incident ray | a.) Spherical mirror |
2.) Concave mirror | b.) Intersection of light rays |
3.) Convex mirror | c.) coming towards mirror |
4.) Real image | d.) Virtual image formed |
5.) Part of sphere | e.) Real image formed |
Answer – 1- c, 2- e, 3- d, 4- b, 5- a.
Q.3.) Define the following questions.
1.) Angle of incidence.
Answer – The angle between the incident ray and the normal at the point of incidence.
2.) Angle of reflection.
Answer – The angle between the reflected ray and the normal at the point of incidence.
3.) Focal length.
Answer – The distance between the pole and the focus of the mirror.
4.) Centre of curvature.
Answer – The centre of the sphere of which the given (spherical) mirror is a part.
5.) Reflection of light.
Answer – The phenomenon, of change in the direction of light rays, when they are fall on a polished surface, is called reflection of light.
Q.4.) Short answers questions.
1.) Type of mirror forms virtual image.
Answer – Concave mirror
2.) Used as a magnifying glass.
Answer – Convex lens
3.) Reflection of light from a plane surface.
Answer – Plane reflection
4.) Reflection of light from non- shiny surface.
Answer – Diffused reflection
5.) Ray of light coming towards mirror.
Answer – Incident ray
Q.5.) Answer the following questions.
1.) Explain Plane of Incidence and the Plane of Reflection.
Answer – Plane of incidence – The plane, defined by the incident ray and the normal at the point of incidence, is called the Plane of incidence.
Plane of reflection – The plane defined by the reflected ray, and the normal at the point of incidence, is called the Plane of reflection.
2.) What is ophthalmoscope?
Answer – Ophthalmoscope is fitted with a concave mirror having a small hole near its centre. The concave mirror helps the doctor to direct a beam of light into the patients eye and see his/her retina clearly through the hole in the mirror.
3.) What is periscope?
Answer – The periscope is a simple device that enables us to see overhead objects that are not directly in the range of our sight.
4.) Explain laws of reflection diagrammatically.