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Tuesday, October 16, 2018



#1.Light travels along straight lines in a medium or in vacuum. The path of light changes only when there is an object in its path or where the medium changes. We call this rectilinear ( straight-line ) propagation of light.

#2.Light that starts from a point A and passes through another point B in the same medium actually passes through all the points on the straight line AB. Such a straight-line path of light is called a ray of light

#3.Light rays start from each point of a source and travel along straight lines till they fall on an object or a surface separating two media (mediums). A bundle of light rays is called a beam of light.

#4.A part from vacuum and gases, light can travel through some liquids and solids. A medium in which light can travel freely over large distances is called a transparent medium. Water, glycerine, glass and clear plastics are transparent. 

#5.A medium in which light cannot travel is called opaque. Wood, metals, bricks,etc.,are opaque

#6.In Materials like oil, light can travel some distance, but its intensity reduces rapidly. Such materials are called translucent.

Saturday, October 13, 2018



#1.Light does not need a material medium to travel, i.e, it can travel through a vacuum too.The best example of this is light travelling from the sun to the earth across vast expanses of space that have no material ( or matter ). Compare this with sound, which is also a wave. Sound needs a material medium to travel.

#2.Light waves travel at a tremendous speed - whose value scientists have fixed at 299,792,458m/s. According to current scientific theories, no material particle can travel at a speed greater than that of light.

#3.The light that enables us to see has a very small wavelength - less than ten thousandth part of a centimetre.In Comparison, the wavelength of audible sound is of the order of a few centimetres to a few metres.

#4.Seeing is one of the most common things we do. when light from an object enters our eyes,we see the object. This light can be that emitted by the object, as in the case of an electric bulb or a red-hot iron nail.It can also be the light bouncing off an object like a book.An Object that emits light is a source of light. During the day, the sun acts as a natural source of light. Candles, Oil lamps and electric bulbs are sources of light made by us.

#5.What is the nature of light? Is it made of material particles like electrons, protons or neutrons,or is it something else? Does a Source of light emit 'particles' of light, or does it cause some kind of wave motion in the space around it ? For centuries, scientist struggled with this question.
Although most common phenomena involving light can be understood by thinking of light as a wave, certain phenomena can be explained only if we think of light as being made up of particles.Scientists now understand that light shows the characteristics of both a wave and a particle.