NCERT Class VII Science Solutions: Chapter 15 – Light Part 3

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Question 9:

Which type of mirror can form a real image?

Answer:

A real image is an image which is located in the plane of convergence for the light rays that originate from a given object.

If a screen is placed in the plane of a real image the image will generally become visible on the screen.

Real images can be produced by concave mirrors and converging lenses, only if the object is placed further away from the mirror/lens than the focal point and this real image is inverted.

This diagram shows Concave mirror

Diagram of Concave Mirror

Question 10:

Which type of lens forms always a virtual image?

Answer:

A concave mirror forms an enlarged image of the object. Therefore, it is used to see an enlarged image of teeth by the dentist.

The image formed by a concave lens is always virtual, upright and erect.

This diagram shows concave lens diagram

Concave Lens Diagram

Question 11:

Choose the correct option:

A virtual image larger than the object can be produced by a

  1. concave lens

  2. concave mirror

  3. convex mirror

  4. plane mirror

Answer:

ii. Concave mirror

Question 12:

Choose the correct option: 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.

  1. 3 m

  2. 5 m

  3. 6 m

  4. 8 m

Answer:

iii. 6 m

Explanation:

As David moves 1 m towards the mirror, the image also moves 1 m towards the mirror. Now the distance between David and mirror is 3 m and the distance between mirror and image is 3 m. So, the total distance between David and his image will be 6 m.

Question 13:

Choose the correct option

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.

Answer:

Explanation:

As the car moves 2 m backward, the mirror also moves 2 m backward, so image comes 2 m forward.

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