Light – Class 7 Science Chapter Notes and Important Questions with Answers
Introduction: The chapter "Light" in Class 7 Science explains the fascinating world of reflection, images, mirrors, and how light enables us to see things around us. Understanding the properties of light not only helps in science exams but also builds a foundation for physics in higher classes. Below, you will find well-explained notes and carefully designed questions with answers that are student-friendly, exam-oriented, and NCERT-based. This post is structured for easy navigation and covers more than 1500 words to provide in-depth preparation support.
📘 Notes of Light – Class 7 Science
What is Light?
Light is a form of energy that enables us to see objects. It travels in a straight line and can be reflected, refracted, or absorbed. Light is essential for vision and plays a central role in many scientific phenomena.
Properties of Light
- Light travels in a straight line (rectilinear propagation).
- Light can be reflected by shiny surfaces such as mirrors.
- Light enables us to see objects when it enters our eyes after reflecting from them.
- Light does not require any medium; it can travel through a vacuum.
Image Formation by Mirrors
Mirrors are polished surfaces that reflect most of the light falling on them. There are two main types of mirrors studied in Class 7:
- Plane Mirror: Produces upright, virtual, and same-size images.
- Spherical Mirrors: Includes concave and convex mirrors.
- Concave mirror: Can produce real and inverted or virtual and magnified images depending on object position.
- Convex mirror: Always produces virtual, upright, and diminished images.
Reflection of Light
Reflection is the bouncing back of light from a surface. There are two types of reflection:
- Regular Reflection: Occurs on smooth surfaces, gives clear images.
- Diffuse Reflection: Occurs on rough surfaces, does not form clear images.
Laws of Reflection
- The angle of incidence is equal to the angle of reflection.
- The incident ray, reflected ray, and normal all lie in the same plane.
Periscope
A periscope is an instrument used to see objects not directly visible, using plane mirrors placed at 45° angles.
Human Eye and Light
The eye is a natural optical device that detects light and enables vision. Light reflected from objects enters the eye, where the lens focuses it onto the retina. The retina sends signals to the brain, and we see the image.
Uses of Concave and Convex Mirrors
- Concave mirror: Used by dentists, in shaving mirrors, and as reflectors in headlights.
- Convex mirror: Used as rear-view mirrors in vehicles because they provide a wider field of view.
Summary of the Chapter
The chapter Light in Class 7 Science teaches the basics of reflection, laws of reflection, plane and spherical mirrors, periscope, and the role of light in vision. Understanding these concepts helps students develop clarity about real-world applications of light and prepares them for higher-level optics.
✍️ Questions and Answers of Light – Class 7 Science
Multiple Choice Questions (MCQs)
- Which of the following is not a luminous object?
(a) Sun
(b) Moon
(c) Torch
(d) Candle
Answer: (b) Moon - The image formed by a plane mirror is:
(a) Real and inverted
(b) Virtual and upright
(c) Magnified
(d) Diminished
Answer: (b) Virtual and upright - Which mirror is used in rear-view mirrors of vehicles?
(a) Plane mirror
(b) Concave mirror
(c) Convex mirror
(d) None
Answer: (c) Convex mirror - The angle of incidence is equal to:
(a) Angle of refraction
(b) Angle of reflection
(c) 90°
(d) 180°
Answer: (b) Angle of reflection - Which instrument uses the principle of reflection of light?
(a) Microscope
(b) Telescope
(c) Periscope
(d) Thermometer
Answer: (c) Periscope - The image formed by a convex mirror is always:
(a) Real and inverted
(b) Diminished and virtual
(c) Same size
(d) Magnified
Answer: (b) Diminished and virtual - In which part of the eye are images formed?
(a) Cornea
(b) Retina
(c) Lens
(d) Iris
Answer: (b) Retina
Very Short Answer Questions
- Define light.
Answer: Light is a form of energy that enables us to see objects. - Name two types of spherical mirrors.
Answer: Concave mirror and convex mirror. - State the first law of reflection.
Answer: The angle of incidence is equal to the angle of reflection. - Give an example of a non-luminous object.
Answer: The Moon. - Which mirror is used by dentists?
Answer: Concave mirror. - What type of image does a plane mirror form?
Answer: Virtual and upright image. - Name an instrument that works on reflection of light.
Answer: Periscope.
Short Answer Questions
- What is the difference between luminous and non-luminous objects?
Answer: Luminous objects emit their own light (e.g., Sun, candle). Non-luminous objects reflect light from luminous objects (e.g., Moon, chair). - Explain regular and diffuse reflection.
Answer: Regular reflection occurs on smooth surfaces and forms clear images, while diffuse reflection occurs on rough surfaces and does not form clear images. - What are the uses of convex mirrors?
Answer: Convex mirrors are used in rear-view mirrors in vehicles as they give a wider field of view and provide diminished, upright images. - Why can’t we see objects in a completely dark room?
Answer: In the absence of light, no rays are reflected from objects to our eyes, so we cannot see them. - Write two uses of concave mirrors.
Answer: Concave mirrors are used by dentists to see enlarged images of teeth and in headlights to focus light beams. - What is a periscope and what is its use?
Answer: A periscope is an instrument made using plane mirrors placed at 45°. It is used to see over obstacles or from a hidden position. - Why is the image formed in a plane mirror said to be virtual?
Answer: Because it cannot be obtained on a screen and appears to be behind the mirror.
Long Answer Questions
- Explain the laws of reflection with a diagram.
Answer: The two laws of reflection are: (1) The angle of incidence equals the angle of reflection. (2) The incident ray, reflected ray, and the normal lie in the same plane. A simple ray diagram can be drawn showing incident ray, reflected ray, normal, and angles. - Describe image formation by a concave mirror with examples.
Answer: The nature of image formed by a concave mirror depends on the object position: at infinity (real, inverted, small), beyond centre (real, inverted, smaller), at centre (real, inverted, same size), between centre and focus (real, inverted, enlarged), at focus (at infinity), between focus and mirror (virtual, upright, magnified). Example: dentist’s mirror for enlarged image. - Explain how we are able to see objects.
Answer: Objects reflect light, which enters our eyes. The lens focuses the light rays onto the retina, which sends signals to the brain through the optic nerve. The brain interprets these signals and forms images. - What is the difference between real and virtual images?
Answer: Real images are formed when rays actually meet; they can be obtained on a screen and are usually inverted. Virtual images are formed when rays appear to meet, cannot be obtained on a screen, and are upright. Plane mirrors form virtual images, while concave mirrors can form both. - How does a periscope work? Mention its principle.
Answer: A periscope uses two plane mirrors at 45° angles. Light from an object reflects from the top mirror, travels through the tube, and reflects from the bottom mirror into the observer’s eyes. It works on the principle of reflection of light. - List the uses of different types of mirrors in daily life.
Answer: Plane mirrors are used in homes and shops for reflection. Concave mirrors are used in headlights, shaving mirrors, and by dentists. Convex mirrors are used as rear-view mirrors in vehicles for a wider view. - What is the importance of light in our daily life?
Answer: Light enables vision, supports photosynthesis in plants, helps in technology (lasers, optical fibers), and is essential in safety and communication. Without light, life on Earth would not exist as we know it.
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