NIOS Class 10 Science Worksheet 15 Questions Answers – Light Energy

This worksheet 15 contains questions based on Chapter 15 Light Energy with complete answers.

This post explains the answers of questions given in the worksheet including explanation, diagrams. These solutions will help you complete your assignments and TMA also.

 Light Energy Worksheet 15 Solution

A complete solution of Questions given in the worksheet 15 of Light Energy of NIOS Class 10 Science.

Q1. Light is the common form of energy. It makes the objects visible to us. Explain how an object becomes visible to us? Is it possible to see an object in the absence of light?

Answer

An object is visible to us when light form the object enters our eyes.

    1.  Luminous objects like the sun, stars, lamp, candle emit their own light which enters our eye and they become visible.

    2. Non-luminous objects do not emit light; they reflect the light that falls on them from a luminous object then they become visible.

So, we see an object when light from it reaches our eyes.

No, it is not possible to seen an object in the absence of light because in the darkness, no light enters our eyes.

 

Q2. Observe your surroundings and list luminous objects. Explain why these objects are known as luminous objects. Differentiate between luminous objects and non-luminous objects.

Answer

We can many luminous objects around us. Some of them are natural and some of them are manmade. The sun, stars are natural sources of light and bulb, burning candle, LED lights, torch etc are man-made luminous objects.

   

These objects are called luminous objects because they emit light which allow us to see them directly.

 

Difference between Luminous and Non-luminous objects

Luminous objects	Non-luminous objects
They emit light.	They do not emit light.
They are visible because they produce light.	They are visible when the reflect light from other sources.
Example – sun, stars, bulb, candle	Example – moon, table, steel plate
They are source of light.	They are not source of light.

 

 

Q3. Perform an activity for formation of images due to reflection. Also differentiate between regular reflection and diffused reflection.

Answer

Activity: Formation of Images due to Reflection

We take a plane mirror and place it vertically on a sheet of paper. Now we hold a pipe (as incident beam of light) at an angle in front of the mirror. We look into the mirror and place another pipe so that its reflection appears to be in a straight line with the image of the first pipe.

Now we adjust the second pipe until the image of the first pipe and the second pipe appear in one straight line. The second pipe represents the reflected ray.

When we try to touch the image, we cannot do that because the image is virtual not real.

Conclusion

The image formed by a plane mirror is virtual, erect and cannot be obtained on the screen.

Difference between Regular Reflection and Diffused Reflection

Regular Reflection	Diffused Reflection
This reflection occurs when light falls on a smooth shiny surface.	This reflection occurs when light falls on rough and uneven surface.
The reflected rays are parallel to each other and goes in certain directions.	The reflected rays go in different directions.
It produces clear and sharp images.	It does not produces clear images.

 

Q4. Put your left hand near a plane mirror. What do you see in the images formed by reflection? the image of your left hand appears as right hand on the image as shown in figure below.

Observe the phenomenon and give reason/reasons for this.

Answer

When we place our left hand rean a plane mirror, the image we see shows it as the right hand. This phenomenon is known as lateral inversion.

Reasons

   1. A plane mirror reverses the image sideways.

   2. It interchanges the left side and the right side of an object.

 

 

 

Q5.A spherical mirror is a section of a hollow sphere whose inner or outer surface is polished. Thus there are mainly two types of spherical mirrors. Name and differentiate two types of spherical mirrors.

Answer

A spherical mirror is a part of a hollow sphere whose one surface is polished. There are two types of spherical mirrors; (i) Concave mirror (ii) Convex mirror

Difference between Concave and convex mirror

Concave mirror	Convex mirror
Its reflecting surface is curved inward.	Its reflecting surface is curved outward.
It converges light rays.	It diverges light rays.
It forms real and inverted images.	It forms virtual and erect images.
It can form magnified images.	It forms diminished images.
Used in solar cooker, headlights, shaving mirrors	Used in safety mirrors, rear mirrors in vehicles.

 

Q6. Dip a pencil in water in a glass tumbler and note down the observation. Repeat the same experiment with different liquids like kerosene or turpentine. Will the observation be same if instead of water we use liquids like kerosene or turpentine? Support your answer with reasons.

Answer

When we dip a pencil in glass tumbler filled with water, the pencil appears bent, broken or raised at the surface.

When we dip the same pencil in kerosene or turpentine, the pencil still appears bet but the amount of bending is different from water.

No, the observation is not same in the different liquids.

Reason

(i)    Different liquids have different refractive indexes. 

(ii)    Refraction depends on the refractive index of the medium.

(iii) Liquid with high refractive index shows more bending and liquid with lower refractive index shows less bending.

 

 

 

Q7. A lens is a portion of transparent refracting medium bounded by two surfaces. List the different types of lenses depending upon the nature of surfaces. Draw the all-possible ray diagrams for image formation in concave lens and convex lens.

Answer

Types of lenses

A lens is made of a transparent refracting medium with tow bounded surfaces. These lenses are of the following types:

(1)      Convex lens: - It is a converging lens

i.     Double convex (biconvex) :- Both surfaces are outward curved.

ii.  Plano – convex: - One surface is plane and other is bulging outward.

iii.   Concavo-convex (Positive meniscus):- One surface is concave and the other is convex.

(2)      Concave lens: - It is a diverging lens

i.  Double concave (Biconcave): - Both surfaces are

curved inward.

ii.    Plano-concave: - One surface is plane/flat and other is concave.

iii.   Convexo- concave (Negative meniscus):- One surface is convex and the other is concave.

 

Ray diagrams for image formation in convex lens

(i)         Object between Focus and lens

(ii)          Object at Focus (F₂)

(iii)       Object between F₂ and 2F₂

(iv)        Object at 2F₂

(v)      Object beyond 2F₂

(vi)      Object between optical centre and Focus (F₂)

Ray diagrams for image formation in concave lens

Q8. We all have seen rainbow (the most colourful phenomenon in nature) after it rains. Explain the phenomenon beyond formation of rainbow. Perform an activity to observe the phenomenon rain-bow and name the colours in a rainbow in sequence.

Answer

Phenomenon behind the formation of Rainbow

A rainbow is formed due to the dispersion, refraction and internal reflection of sunlight in tiny water droplets present in the atmosphere at the time of rainfall.

Process of formation of rainbow

When sunlight enters a raindrop, it bends because water is denser than air, this is refraction of light.

Each droplet work as a prism so light splits into seven colours -violet, indigo, blue, green, yellow, orange, red. This happens due to dispersion of light.

The light hits the inner surface of raindrop and it reflects back; this is internal reflection.

Now light comes out of the drop and refracts again and all the colours spread in the sky forming a seven coloured rainbow which is a natural spectrum.

Activity to observe Rainbow

Materials Used

   1. Cardboard box

   2.  Whitepaper

   3. Glass prism

   4.  Knife

   5.  Light source (sunlight)

Procedure

We take an empty cardboard box and make a rectangular opening on its cover. We paste a sheet of transparent white paper over this opening.

 On the opposite side of the box, we cut thin slit using a knife. We place a prism on a block inside the box in the path of light and turn the slit side towards sunlight so that sunlight enters the box through the slit. We observe the transparent white paper.

Observation

We see a coloured strips appear on the transparent white paper. There are seven colours – violet, indigo, blue, green, yellow, orange, and red.

Explanation

Sunlight is made up of seven different colours. When sunlight passes through a prism, each colour bends at different angle due to refraction.

Violet colour deviates maximum and red colour deviates minimum.

These seven colours - violet, indigo, blue, green, yellow, orange, and red (VIBGYOR) form a strip on the screen and this colourful strip is called spectrum.

The phenomena of splitting of white light into seven colours is called dispersion of light.

Conclusion

 This activity proves that sunlight is made up of seven colours. The activity also explains the ‘Dispersion of light’.

Colours of the Rainbow in sequence

Violet, indigo, blue, green, yellow, orange, red

 

 

Q9. All the different parts of our eyes work together to help us see. Draw image formation in eye and explain the different defects in the eye.

Answer

Image formation in eye

Light from the object enters the cornea, passes through aqueous humour, eye lens and vitreous humour and focuses on the retina.

The image formed is real, inverted and diminished

 

Defects in the eye

Following are the main defects of vision

i.   Myopia (short-sightedness)

ii.  Hypermetropia (Long sightedness)

iii.Presbyopia

iv.  Astigmatism

i.   Myopia: - The person with this defect can see near object clearly but cannot see distant objects clearly. Concave lens is used to correct this defect.

ii.   Hypermetropia: - The person with this defect can see distant objects clearly but cannot see nearby objects. Convex lens is used to correct this defect.

iii.  Presbyopia: - The person with this defect cannot see both near and far objects clearly. This defect occurs in old age. Bifocal lens is used to correct this defect.

iv.   Astigmatism: - The person with this defect cannot see horizontal and vertical lines clearly at the same time. A cylindrical lens is used to correct this defect.

 

Q10. If image of the object does not form at retina of the eye has some defects of vision. Observe your surroundings and list the common defects of vision and how these defects can be removed.

Answer

When image of the object is not formed at retina of the eye, the eye is called defective eye. Following are the main eye defects: -

i.  Myopia (short-sightedness)

ii.  Hypermetropia (Long sightedness)

iii.Presbyopia

iv.Astigmatism

i.   Myopia (short-sightedness)

Observation: - Person cannot see distant objects clearly but can see nearby objects.

Reason: - image of distant object forms before the retina because eye ball becomes longer than usual.

Correction: - Concave (diverging) lens is used.

ii.   Hypermetropia (Long sightedness)

Observation: - Person cannot see nearby objects clearly but can see distant objects.

Reason: - image of nearby object forms behind the retina because eye ball becomes shorter than usual.

Correction: - Convex (converging) lens is used.

iii.  Presbyopia

This defect occurs in old age.

Observation: - Person cannot see both distant objects and nearby objects clearly.

Reason: - Ciliary muscles become weak and flexibility of lens decreases.

Correction: - Bifocal lens (upper part concave and lower part is convex)

iv. Astigmatism

This defect occurs in old age.

Observation: - Person cannot see horizontal and vertical lines clearly at the same time.

Reason: - Cornea is not perfect spherical.

Correction: - Cylindrical lens is used