8th Class Science Light Sources of Light

     Sources of Light

A great deal of light reaches our eyes from luminous surfaces. To make thepoint clear, imagine how your room would appear if the walls and other surfacesare covered with black paint that reflects no light. White ceilings or brightwalls reflect and diffuse much of the light they receive and hence increase thebrightness of the room. In fact when we use indhrect lighting, we hide thelamps from sight and the light reach us after being reflected from the wallsand ceiling. For example, the Moon, which we often think of as a source oflight at night is actually an indirect-lightning device, reflecting sunlight.

There are different sources from which we get light. For example, the Sun, thestars, candle, burning wood, electric bulb etc. Some sources have their ownlight, where as, others reflect light of different sources. There are, therefore,two types of the sources of light:

(i) Luminous

(ii) Non-Luminous

         Luminous Sources

The luminous sources are those that have the light of their own. For example,the Sun, the star, etc.

          Luminious Sources

These objects have their own internal sources of energy. They keep on producinglight continuously.

           Non Luminous Sources

The sources that do not have the light of their own, but produces light derivingenergy from other sources. For example, the burning candle, electric bulb, etc.

   Non Luminous Sources    

         The ability of an animal to see an object is only due to the light. Ifthere is no light, it will not be possible to see any object. Hence wecan say that light is a form of energy, which produce the sensationof_________.

(a) Vision

(b) Taste

(c) Hearing

(d) All of these

(e) None of these

Answer:(a)

Explanation

Light is a form of energy which produces the sensation of vision.

Therefore, option A is correct and rest of the options is incorrect.

         There are some objects in this Universe that have the light of theirown, but there are some other objects having no light of their own.Depending on this property, there are two types of objects, luminousand non-luminous. Luminous or Non-Luminous nature of the objectdepends on which one of the following properties?

(a) Nature of material

(b) Quantity of material

(c) State of material

(d)All of these

(e) None of these

Answer: (a)

Explanation

It is the nature of the materials which determines whether the body isluminous or non luminous.

      David have some objects with him. Which one of the following objectsis luminous?

(a) Wood

(b) Iron

(c) Plastic

(d) Radium

(e) None of these

Answer: (d)

Explanation

Among the article given above only radium is luminous and rest are nonluminous.

         Thomas went to the science laboratory with his friend James. Heexplained him about the luminous and non luminous objects withthe help of the instruments present in the lab. At the end, heexplained him that a dry cell is a source of energy and can producelight if connected to a bulb, but it is a non luminous object. Was hisstatement correct?

(a) Correct

(b) Incorrect

(c) Partially correct

(d) All of these

(e) None of these

Answer: (a)

Explanation

The statement given above shows that battery posses chemical energy,hence is a source of energy, but not the luminous object..