Class 7_Light
- 2. WHAT IS LIGHT? • Light is a radiation or a form of energy that our eyes can detect. Light enables us to view our surroundings. • Light travels from one place to another in a straight line.
- 3. DOES LIGHT TRAVEL IN STRAIGHTLINE? • The path of light gets blocked when an object covers the source of light. • This is illustrated by trying to see the flame of a candle using a straight pipe and then with a bent pipe. • This proves that light travels in a straight line.
- 5. REFLECTION • When light is incident on a certain surface, it either gets reflected or bounces back. • Such surfaces are really well polished and act like a mirror. The phenomenon of light bouncing off surfaces is called reflection. • A mirror that has a plane surface is called a Plane Mirror. • A mirror that is curved, it either bulges in or out, is called a Curved Mirror.
- 6. WHAT IS AN IMAGE? • As a mirror reflects light, an image of the object that is in front of the mirror is formed on it. • The image of an object can be defined as the impression of the object created by the light on the mirror. • The distance between the image and the mirror, and the object and the mirror always remain the same. • If we increase or decrease the distance between the object and the mirror, the distance between the image and the mirror also increases or decreases, respectively.
- 7. LEFT-RIGHT INVERSIONOF THE IMAGE • The image formed by the mirror is always left-right inverted. • This means that the right side of the object appears as the left side of the image, and the left side of the object appears at the right side of the image.
- 8. THE LAWS OF REFLECTION OF LIGHT
- 9. • Incident Ray - The light ray that falls on the reflecting surface is called an Incident Ray. • Reflected Ray - The light ray that gets reflected back from a reflecting surface is called a Reflected Ray. • Normal - It is a line that is perpendicular to the reflected plane at the point of incidence of Incident Ray.
- 10. INCIDENT RAY, REFLECTED RAY AND THE NORMAL AT THE POINT OF INCIDENCE LIE IN THE SAME PLANE
- 11. TYPES OF REFLECTION • Diffused Reflection or Irregular Reflection --> • Regular Reflection -->
- 12. SPHERICAL MIRRORS • A spherical mirror (or curved mirror) is a mirror which has the shape of a piece cut out of a spherical surface. • They are of 2 types: Concave and Convex.
- 13. REALIMAGEAND VIRTUALIMAGE Real Image Virtual Image The real image is formed when the light rays reflect and meet at the same point. A virtual image is formed when light rays reflect and diverge from the same point. It can be viewed on a screen. It cannot be viewed on the screen. It is always inverted. It is always erect. Formed by Concave mirror Formed by Convex, Concave and Plane Mirrors
- 15. THE IMAGE FORMED BY A CONCAVE MIRROR • It can either be real or virtual. • It can either be inverted or erect. • It can have the same size as that of the object, a larger size that of the object or smaller size than that of the object.
- 16. THE IMAGE FORMED BY A CONVEX MIRROR • It is always virtual. • It is always upright (erect). • It is smaller in size as that of the object.
- 17. APPLICATION OF CONCAVE MIRRORS • Satellite dishes use a concave mirror to gather all the signals and reflect them on a certain point. • Dentists use a concave mirror to reflect light on a particular tooth. • Shaving Mirrors are concave in shape. • Headlights of a car have a concave mirror so that we can reflect back light straight on the path. • Torches also use concave Mirrors.
- 18. APPLICATIONOF CONVEX MIRRORS • The rear view mirrors are convex mirrors as they provide a wider view of the road behind. • Security mirrors near an ATM are convex so that the user can detect easily if anyone else is watching from behind or not.
- 19. LENSES A lens is a part of a reflecting material like glass or plastic but curved from both sides. Lenses are unlike mirrors that have a reflecting surface only on one side. Depending upon its shape a lens can be categorized as: • ConvexLens - A Convex Lens is curved outwards. It is thicker in the centre and narrows down at the edges. It merges the light rays passing through it at a certain point. Therefore, it is also called a Converging Lens. • ConcaveLens - A Concave Lens is curved inwards. It has wider edges and a thinner centre. It reflects back the light that travels through it in different directions. Therefore, it is also called a DivergingLens.
- 21. IMAGES FORMED BY CONVEX AND CONCAVE LENSES A Convex lens forms an image that is: • real • inverted • the image is large and appears close to the lens A Concave lens forms an image that is: • virtual • erect • small and appears far away
- 22. IMAGE FORMED BY CONVEX LENS AT DIFFERENT DISTANCE
- 23. VIRTUAL IMAGE FORMED BY THE CONVEX LENS IMAGE FORMED BY THE CONCAVE LENS
- 24. REFRACTION • The bending of the path of light when it moves from one medium to another is known as refraction. • The object we see after refraction is called the apparent object. • There exists some displacement between the apparent and actual object.
- 25. WHAT IS A RAINBOW? • A rainbow is a natural phenomenon in which the light rays of the sun are reflected and refracted by the water droplets present in the atmosphere. • A rainbow appears as an arc on the sky that contains a band of seven colors – Red, orange, yellow, green, blue, indigo and violet.
- 26. RAINBOW The white light of the sun contains seven colored lights in it that separate out due to refraction (called a Spectrum of Lights). This spectrum of white light can be seen in the following: • Rainbows • Soap bubbles • Surface of a CD • Prisms
- 27. DISPERSIONOF WHITE LIGHT THROUGH PRISM • Sunlight may appear as white but in fact, is made up of seven component colors. This can be observed when a beam of sunlight is passed through a triangular prism or when light falls on a compact disk (CD). • The seven colors that appear are violet, indigo, blue, green, yellow, orange and red. These are also the colors of a rainbow we see after a rainfall. • The splitting of white light into its component colors is called dispersion.
- 28. NEWTON'S DISC • The Newton’s disc can be obtained by dividing a disk into 7 partitions and painting each of them with the seven colors of the rainbow. • When the disc is rotated at a fast pace in daylight all the colors tend to mix together and the disc appears whitish in color.