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NCERT Solutions for Class 7 Science Chapter 11: Light

Access expert NCERT solutions for Class 7 Science Chapter 11, focusing on the concept of Light.

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NCERT Solutions for Class 7 Science Chapter 11: Light

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  1. Light This chapter explores the fascinating world of light and its properties. Here’s a breakdown of the key concepts: What is Light? ● Light is a form of energy that allows us to see objects. ● It travels in straight lines and cannot be felt. ● Our eyes detect light and send signals to our brain, allowing us to perceive our surroundings. Sources of Light: ● The sun is the primary source of light on Earth. ● Other sources include fire, electric lamps, stars, and even some living things like fireflies. Properties of Light: ● Reflection: When light strikes a smooth surface, it bounces back. This is why we can see ourselves in mirrors. ● Refraction: When light travels from one medium (like air) to another (like water), it bends. This is why a straw appears bent when placed in a glass of water. ● Shadows: Opaque objects block light, creating areas of darkness called shadows. Uses of Light: ● We use light for essential tasks like seeing, reading, and working. ● Light also plays a role in communication (think traffic lights) and medical procedures. Safety:

  2. ● Looking directly at the sun can damage your eyes. Understanding light is crucial for many everyday experiences and technological advancements. Additionally, you might have learned about: ● Different types of mirrors (plane and curved) and how they reflect light. ● How lenses can focus or spread out light rays. ● The concept of color as a property of light. Exercises Q.1.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. Ans : (a) Virtual image. (b) Always virtual and smaller in size.

  3. (c) Plane (d) Real (e) Lens 2. State the following statement true or false (a) We can obtain an enlarged and erect image by a convex mirror. (b) A concave lens always form a virtual image. (c) We can obtain a real, enlarged and inverted image by a concave mirror. (d) A real image cannot be obtained on a screen. (e) A concave mirror always form a real image. Ans : (a)False (b)True (c) True (d) False (e) False 3. Match the items given in Column I with one or more items of Column II Column I Column II

  4. A plane mirror Used a magnifying glass A convex mirror Can form image of objects spead over large area A convex lens Used by dentists to see enlarged image of teeth A concave mirror The image is always inverted and magnified A concave lens The image is erect and of the same size as the object The image is erect and smaller in size than the object Ans : Column I Column II A plane mirror The is erect and of the same size as the object A convex mirror Can form image of objects spead over large area A convex lens Used as a magnifying glass A concave mirror Used by dentists to see enlarged image of teeth A concave lens The image is erect The image is erect and smaller in size than the objectof the same size as the object

  5. 8. Give one use each of a concave and a convex mirror. Ans : ● Concave mirror: Reflecting telescopes use concave mirrors to gather and focus light from distant objects, creating magnified images. ● Convex mirror: Convex mirrors are commonly used as rearview mirrors in vehicles because they provide a wider field of view, allowing drivers to see a larger portion of traffic behind them. 9. Which type of mirror can form a real image? Ans : Only concave mirrors can form real images. 10. Which type of lens forms always a virtual image? Ans : A concave lens always forms a virtual image. 11. A virtual image larger than the object can be produced by a (i) concave lens (ii) concave mirror (iii) convex mirror (iv) plane mirror Ans : Only a concave mirror can magnify an image by creating a virtual image larger than the object. 12. David is observing his image in a plane mirror. Die 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 Ans : 6m

  6. 13. 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 mew 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 Ans : 4 m/s

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