Class 7 Science Chapter 11 Notes Light
→ Concave lens : It is also known as diverging lens. It is thinner at the centre than at the edges. It diverges a beam of light on reflection through it. Concave lenses have a virtual focus.
→ Concave mirror : A mirror in which reflecting surface of the spherical mirror is curved inwards is called concave mirror.
→ Convex lens : Convex lenses are thicker at the centre and thinner at the edges.
It converges a parallel beam of light on refraction through it. It has a real focus.
→ Convex mirror : The type of mirror who is reflecting surface of the spherical mirror is curved outwards, it is called convex mirror.
→ Erect image : When the image is formed have same direction as that of object, then the formed image is called erect image.
→ Magnified image : When the size of the image is larger than the object, then it is called magnified image.
→ Magnifying glass : A magnifying glass is a convex lens that is used to produce a magnified image of an object.
→ Prism : It is a transparent glass pyramid, bounded by four triangular surfaces that separates white colour into a spectrum of colours.
→ Rainbow : A band of seven colours are formed in the sky in the direction opposite to the sun due to rain or presence of water droplets in the atmosphere.
→ Real image : The image which can be formed or obtained on the screen is known as real image.
→ Rear view mirror : Rear view mirror is a mirror in automobiles and other vehicles designed to see a virtual, upright and image of the traffic behind them. For review mirror, convex mirror is used.
→ Side mirror : The rear view mirror is used as a side mirror in motor vehicles.
→ Spherical mirror : The mirrors which have curved surfaces are known as spherical mirrors.
→ Virtual image : The image that cannot be obtained on the screen is a known as virtual image.
→ Rear view mirror : Rear view mirror is a mirror in automobiles and other vehicles, designed to see a virtual, upright and image of the traffic behind them. For review mirror, convex mirror is used.
→ Side mirror : The rear view mirror is used as a side mirror in motor vehicles.
→ Spherical mirror : The mirrors which have curved surfaces are known as spherical mirrors.
→ Virtual image : The image that cannot be obtained on the screen is a known as virtual image.
→ Light is a form of energy. It travels in a straight line. This property of light is known as rectilinear propagation of light.
→ When light falls on an object, some of it is absorbed and the rest is bounced back.
→ The phenomenon of bouncing back of light from a surface is known as reflection of light. Reflection of light depends upon the nature of object through which it passes.
→ Light passed through gas, absorbed by unpolished wood and reflected by mirror.
→ Regular reflection takes place on an even surface or a shining surface like mirror. Regular reflection results in the formation of an image.
→ Uneven or rough surface reflects light in all directions. This reflection is known as diffused reflection. It does not result in the formation of an image.
→ An image that cannot be formed on a screen is called a virtual image. Rays of light do not actually pass. through a virtual image.
→ An image that can be formed on a screen is called a real image. The image is formed by rays of light actually meeting a point.
→ Mirrors are of two types: plane and spherical.
→ A plane mirror is a flat smooth glass surface which is polished by silver on one of its sides and the other side is used as the reflecting surface.
- Radius of curvature and focal length of a plane mirror is infinite.
- The image formed in a plane mirror is always erect and cannot be obtained on a screen.
- The size of the image is equal to the size of the object and is laterally inverted.
- The image is formed at the same distance from the mirror as the object is kept in front of it.
→ Spherical mirrors are of two types: concave and convex.
→ A concave mirror can form a real as well as an inverted image. When the object is placed very close to the mirror, the image formed is virtual, erect and magnified.
→ Image formed by a convex mirror is erect, virtual and smaller in size than the object.
→ Lens is a transparent medium bounded by two surfaces of which at least one is spherical.
→ Blue, green and red are the three primary colours of white light. Other colours can be obtained by mixing the primary colours.
- Red + Green = Yellow
- Red + Blue = Magenta
- Blue + Green = Cyan
- Red + Bitte + Green = White