NCERT Solutions for Class 7 Science Chapter 15 : Light

Q:

The rear view mirror of a car is a plane mirror. A driver is reversing his car at a speed of 2 m/s. The driver sees in his rear view mirror the image of a truck parked behind his car. The speed at which the image of the truck appears to approach the driver will be (i) 1 m/s (ii) 2 m/s (iii) 4 m/s (iv) 8 m/s

A:

Correct option is (iii).

Explanation:

Speed of truck in the mirror = 2v

where v is original speed.

Speed of truck in the mirror = 2 × 2 m/s = 4 m/s

Q:

David is observing his image in a plane mirror. The distance between the mirror and his image is 4 m. If he moves 1 m towards the mirror, then the distance between David and his image will be (i) 3 m (ii) 5 m (iii) 6 m (iv) 8 m

A:

Correct option is (iii).

Explanation:

Distance between the mirror and David’s image = 4 m

If David moves 1 m towards the mirror, then his distance from the mirror = 4 m − 1 m = 3 m

Therefore, the distance between David and his image  = 3 m + 3 m = 6 m

Q:

A virtual image larger than the object can be produced by a (i) concave lens (ii) concave mirror (iii) convex mirror (iv) plane mirror

A:

Correct option is (ii).

Explanation:

When the object is placed very close to the concave mirror, the image formed is virtual, erect and magnified.

Q:

Which type of lens forms always a virtual image?

A:

Concave lens always forms a virtual image.

Q:

Which type of mirror can form a real image?

A:

Concave mirror can form a real image.

Q:

Give one use each of a concave and a convex mirror.

A:

Use of concave mirror:

As concave mirror produces large magnified image, it is used by the doctors to examine eye, ears, nose and throat etc.

Use of convex mirror:

Convex mirror forms small and virtual image due to which it is used as the side rear view mirror in vehicles to see the large area for a better view of traffic on road.

Q:

What is a virtual image? Give one situation where a virtual image is formed.

A:

The image which cannot be obtained on a screen is called a virtual image. When we see ourselves in a plane mirror, the image formed cannot be obtained on a screen. It is one of the situations where a virtual image is formed.

Q:

State the characteristics of the image formed by a plane mirror.

A:

The characteristics of the image formed by a plane mirror are as follows:

  1. Image is erect and virtual.
  2. Image is formed at the same distance behind the mirror as the object is placed in front of the mirror.
  3. Image is of the same size as that of the object.
  4. Image is laterally inverted.

Q:

State two differences between a convex and a concave lens.

A:

The two differences between a convex and a concave lens are as follows:

  1. A convex lens forms a real and inverted image while a concave lens forms a virtual and erect image.
  2. A convex lens can also form a virtual and erect image when object is placed very close to it whereas, a concave lens cannot form a real and inverted image at all.

Q:

Find out the letters of English alphabet or any other language known to you in which the image formed in a plane mirror appears exactly like the letter itself. Discuss your findings.

A:

The letters of English alphabets, whose image formed by the plane mirror is exactly like the letter itself, are as follows:

A, H, I, M, O, T, U, V, W, X and Y

All of these letters can be divided into two equal halves through a vertical plane. Therefore, even their images after undergoing lateral inversion would appear same as that of letter itself. Thus, we can say that all vertically symmetrical objects will produce image same as themselves when placed in front of a plane mirror.

Q:

Match the items given in Column I with one or more items of Column II.
Column I Column II
A plane mirror Used as a magnifying glass
A convex mirror Can form image of objects spread over a large area
A convex lens Used by dentists to see enlarged image of teeth
A concave mirror The images is always inverted and magnified
A concave lens The images is erect and of the same size as the object
The image is erect and smaller in size than the object

A:

The correctly matched contents of Column I and Column II are as follows:

Column I

Column II

A plane mirror

The images is erect and of the same size as the object

A convex mirror

Can form image of objects spread over a large area

A convex lens

Used as a magnifying glass

A concave mirror

The images is always inverted and magnified

Used by dentists to see enlarged image of teeth

A concave lens

The image is erect and smaller in size than the object

 

Q:

Mark ‘T’ if the statement is true and ‘F’ if it is false:
(a) We can obtain an enlarged and erect image by a convex mirror. (T/F)
(b) A concave lens always form a virtual image. (T/F)
(c) We can obtain a real, enlarged and inverted image by a concave mirror. (T/F)
(d) A real image cannot be obtained on a screen. (T/F)
(e) A concave mirror always form a real image. (T/F)

A:

(a) False

(b) True

(c) True

(d) False

(e) False

Q:

Fill in the blanks: (a) An image that cannot be obtained on a screen is called____________. (b) Image formed by a convex __________ is always virtual and smaller in size. (c) An image formed by a __________ mirror is always of the same size as that of the object. (d) An image which can be obtained on a screen is called a _________ image. (e) An image formed by a concave ___________ cannot be obtained on a screen.

A:

(a) An image that cannot be obtained on a screen is called virtual image.

(b) Image formed by a convex mirror is always virtual and smaller in size.

(c) An image formed by a plane mirror is always of the same size as that of the object.

(d) An image which can be obtained on a screen is called a real image.

(e) An image formed by a concave lens cannot be obtained on a screen.

Benefits of NCERT Solutions

Following are some of the benefits of using NCERT Solutions by Extramarks.

1. The NCERT solutions for class 7 are prepared keeping in mind the necessary rules and format issued by the CBSE board thus providing students much-needed preview of the exam pattern of questions and preview of the exam that they are going to face during the final exams.

2. The students can be sure about the quality of the solutions as they are committed by highly experienced and expert teachers. These teachers have years of experience and they make sure that there is no mistake committed when preparing the solutions.

3. The NCERT 7 solutions are provided for the questions that are most likely to appear in the exam thus improving the efficiency of the students by helping them prepare for the important parts of the syllabus.

Tips & Strategies for Class 7 Exam Preparation

1. Start your revision early so you can revise well and grasp all the difficult concepts.

2. Organize your study time by making a timetable as it will help you manage your time accordingly.

3. Take mock tests and solve sample papers as they will help you learn time management during the exam and make you familiar with the exam pattern.

4. Take regular breaks, look after yourself by sleeping properly and eating well.

5. Know your exam well, explore the mock tests, and practice sample papers as much as you can.

Why Choose Extramarks CBSE Class 7 Study Materials?

1. The solutions have been compiled keeping in mind the purpose of scoring high marks in exams thus they have everything that the students need to prepare for exams.
2. The NCERT solutions for class 7 are designed in a clear and simple language complete with diagrams so that the students understand the subject well.
3. The NCERT 7 solutions are accurate thus improving their reliability.
4. The solutions are designed by expert and experienced teachers that help in removing all doubts out of the solutions and improving the credibility of the answers.

Frequently Asked Questions

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Is class 7 Math NCERT book sufficient for prepare for the exams?

Yes, the NCERT book has been designed keeping in mind the pattern of paper that will be presented in the exam to students. The NCERT book is sufficient to study for the exam as it has everything related to the exam and contains all information out of which the questions will be asked in the exam. But if you want to prepare a little bit extra, we suggest that you go through the NCERT class 7 solutions.

When to refer to NCERT solutions for class 7th?

When you are studying the NCERT book for math and other subjects for your class 7 exams, refer to the NCERT class 7 solutions simultaneously so you can see where you are going wrong and what are you getting right in your exercises’ attempt.

Why are the NCERT solutions important for Class 7th?

The class 7th is very crucial as it is among the major middle school classes during which the child’s base is formed in math and science and even in other subjects like English. Thus, it is students must study smartly in this class and ace their exams while getting all the help they need from the NCERT 7 solutions given by Extramarks.

Can I rely on the NCERT solutions for class 7 Math at Extramarks to perform well in the annual exam?

Yes, absolutely. The NCERT solutions provided by Extramarks for class 7 are eloquent and elaborate at best and are thus useful for students studying for the final exams of class 7. The students will have many questions and doubts regarding the NCERT solutions for class 7 and this is why the solutions have been elaborated well to help students understand the answers to exercises.

Do you provide NCERT solutions for Class 7 Math for free?

Yes, the NCERT solutions for Math and other subjects for class 7 are available for free from Extramarks.

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