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### 56 Cards in this Set

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 Define reflection When a ray of light falls on an opaque object some of it bounces back off that surface. This bouncing back of light is called reflection. What is incident ray? The ray of light carrying light from the source is called incident ray. What is reflected ray? The ray of light carrying the reflected light from the surface of the object is called reflected ray. Define Angle of incidence Angle between the incident ray and the normal. Define Angle of reflection Angle between the reflected ray and the normal. State the Laws of reflection 1. When a ray of light falls on a mirror, it is reflected in such a way that the angle of incidence is equal to angle of reflection. 2. The incident ray, the normal at the point of incidence and the reflected ray all lie in the same plane. What is the angle of incidence in a periscope? 45 degree What is the angle of reflection in a periscope? 45 degree What are optical fibres? Optical fibres are very fines strands of glass. They have a core of pure glass coated with a special material which reflects light. Thus with repeated reflections the light rays can travel without losing their intensity. Where are optical fibres used? In endoscopes, telecommunications. What is regular reflection? When the reflection takes place from a perfect plane surface, the angle of incidence is equal to the angle of reflection. If parallel beams of light emerge parallel to each other this reflection is called regular reflection. What is diffused / irregular reflection? When reflection take splace from a rough surface, the incidence and reflection angle may be equal but, the parallel beams of incident light will not emerge parallel. Such reflections are calleed diffused reflection. State the properties of an image formes by a plane mirror. A plane mirror forms an image 1. of the same size as the object 2. as far behind the mirror as the object is in front of it. 3. of erect nature 4. which is laterally inverted. What is a real image? When the image is formed by the actual intersection of reflected rays it forms a real image. Theses can be caught on a screen. What is a virtual image? If the image formed by reflected rays which appear to diverge from a point or a line, is called a virtual image. These cannot be caught on a screen. State 3 uses of a plane mirror At homes in bathroom, dressing table developing a kaleidoscope Making a periscope. Define centre of curvature. The geometrical centre of the sphere of which the mirror forms a part is called centre of curvature. Define pole of a mirror. The geomitrical centre of the mirror formed is called the pole. Define radius of curvature The radius of the sphere of which the curved surface forms a part is called the radius of curvature. Define Principal axis. The line passingg through the pole and the centre of curvature is called principal axis. DEfine principal focus. The rays of light parallel to the principal axis incident on a concave mirror after reflection converge at a certain pont on the prinipal axis. This point is called principal focus. If an incident ray from the focus falls on the mirror, what will happen to it after reflection? The ray becomes parallel to the axis after reflection. If the incident ray travels along the principal axis, what will be the angle of incidence be? How will this ray be reflected? Angle of incidence = 0 degree After reflection the ray is reflected along the axis. Define radius of curcature. The radius of the sphere of which the curved surface forms a part is called the radius of curvature. State the properties of the image if the object is on the axis beyond the the centre of curvature. Image is real inverted diminished State the properties of the image if the object is on the centre of curvature. Image is Real Inverted Same size State the properties of the image if the object is on the axis between the centre of curvature and the focal point. Image is Real Inverted Magnified State the properties of the image if the object is on the axis between the mirror and the focal pont. Image is Virtual Upright magnified State the properties of the image if the object is at infinity. Image is Real, formed on the focal point Inverted Diminished State the properties of the image if the object is on the axis on the focal point. Image is formed at infinity blurred highly magnified State the properties of the image formed in a convex mirror. Whatever be the position of the object, the image formed is virtual , behind the mirror between the pole abd the focus Erect Diminished Differences between concave and convex mirror Concave 1. reflection takes place on the curved surface 2. has a real focus 3. forms image according to the position of object. CONVEX MIRROR 1. Reflection takes place on the bulging part of the mirror. 2. Virtual focus. 3. Image formed always virtual, erect, diminished If any ray passes parallel to the principal axis where will it pass through after reflection? The focus. If any ray passes through the focus where will it pass through after reflection? tThe reflected ray will be parallel to the principal axcis after reflection. If any ray passes through the centre of curvature where will it pass through after reflection? It is reflected along the same direction. If any ray falls at the pole at some angle where will it pass through after reflection? It will emerge at the same angle on the other side of the principal axis. Uses of the concave mirror Solar Cookers Shaving glasses in saloons Astronomical telescopes Used by dentists Torches, search lightsn headlights of a car Uses of convex mirror Rear view mirror of a car Can be used when larger focal view is required. How does the searchlight work? The source if light is placed at the focus so that after reflection, a strong bright parallel beam is available to guide ships at sea State the relation between focus (F) and Centre of curvature (C) C = 2 F or F= 1/2 C focal length is half radius of curvature Differences between regular and irregular reflection Regular Reflecton - takes place on a smooth surface Image is formed after reflection Light is reflected back in a definite direction into the same medium Irregular reflection 1. Takes place on a rough surface. 2. No image is formed after reflection 3. Light is scattered back into the same medium in all directions. Define virtual image The image formed when the reflected rays appear to meet each other but actually do not intersect with each other in reality. Cannot be cast on a screen. Is always erect. A ray of light strkes the plane mirror making an angle of 20 degrees with the plane mirror. What is the angle of reflection? Angle between the incident ray and the normal, that is the angle of incidence = 90 - 20 = 70 degrees. Hence angle of reflection = 70 degrees. What kind of mirror is used to obtain a real image? A concave mirror What kind of mirror is used to obtain a virtual image smaller than the object? A convex mirror What kind of mirror is used to obtain a virtual image having the same size as the object? A plane mirror What kind of mirror is used to obtain a virtual magnified image? Concave mirror Give one word for Ray of light falling on an object Incident ray Give one word for Ray of light turned or bounced back on an object Reflected ray Give one word for The point at which a ray of light falls on an object Point of incidence Phenomenon of bouncing back of light Reflection If the angle between the incident ray and the normal on a plane mirror be doubled, the angle between the reflected and the normal will become DOUBLE If the radius of curvature of a spherical mirror be doubled then its focal length will become double The image of an object placed in front of a plane mirror is virtual and erect The focal length of a plane mirror is equal to infinity the image of the objectplaced at infinity formed on a concave mirror is formed at the focus