Name: ______________________ The City SchoolSec: _________ Prep Girls North Nazimabad Class-8Worksheet: Light

1. White light is observed when light of _______ wavelengths strike the retina. 2. Primary colors of light are three colors of light which when mixed together produce white light.There are many different sets of primary light colors. Interestingly enough, the eye contains threetypes of color sensors (nerve cells) that sense the entire span of the visible light spectrum. Each ofthe three types of cells senses a range of colors; yet they are most sensitive to a specific light color. The most common set of three primary light colors are those that correspond to the three colors thatthe nerve cells are most sensitive to. What are these three primary colors?

_____________________________________________________________________________________________

3. By combining pairs of these three primary colors in equal intensity, one can produce the secondary colors of light. State the pairs and the secondary colors they produce. Then fill in the color wheel tothe right.

4. Two lights are arranged above a white sheet of paper. When thelights are turned on they illuminate the entire sheet of paper (asseen in the diagram at the right). Each light bulb emits a primarycolor of light - red (R), green (G), and blue (B). Depending onwhich primary color of light is used, the paper will appear adifferent color. Express your understanding of color addition bydetermining the color that the sheet of paper will appear in thediagrams below.

5. Complementary colors of light are combinations of two light colors that can be mixed together inequal intensities to produce white light. Thus, the complementary color of ... a. ... red light is ____________________ light. b. ... green light is ____________________ light.

c. ... blue light is ____________________ light. 6. The Rule of Color Subtraction: An understanding of complementary colors assists inunderstanding the color appearance of objects when viewed under white light. Whenever an objectsubtracts a color from white light, it appears as the complementary color. If an object absorbs cyanlight, then it will appear as red. Conversely, an object that appears as red is an object that absorbscyan light. Use these ideas to complete the following statements.

When viewed under white light (RGB), a ... a. ... red shirt will absorb ________________ light and reflect ________________ light. b. ... green shirt will absorb ________________ light and reflect ________________ light. c. ... blue shirt will absorb ________________ light and reflect ________________ light. d. ... cyan shirt will absorb ________________ light and reflect ________________ light. e. ... magenta shirt will absorb ________________ light and reflect ________________ light. f. ... yellow shirt will absorb ________________ light and reflect ________________ light. g. ... black shirt will absorb ________________ light and reflect ________________ light.

7. Express your understanding of complementary colors and the rule of color subtraction by

completing the following three diagrams. White light (red-green-blue) is shown incident on a sheetof paper that is painted with a pigment that absorbs one of the primary colors of light. For eachdiagram, label the color of the two reflected colors and label the color that the paper appears.

8. The mathematics of color has little to do with numbers and much to dowith the addition and subtraction of colors. The addition of two colors of light results in a new color. Use the color wheel at the right and the conceptof complementary colors to complete the following color equations. (W =white; R = red; G = green; B = blue; C = cyan; M = magenta; Y =yellow) a. R + G = ______ b. R + B = ______ c. G + B = ______ d. R + C = ______ e. G + M = ______ f. B + Y = ______ g. W - R = ______ h. W - G = ______ i. W - B = ______ j. W - C = ______ k. W - M = ______ l. W - Y = ______ m. W - R - C = ______ n. W - G - B = ______ o. W - M - G = ______

1. Draw a diagram to show the reflection of light from a plane mirror. Label the following on the diagram: (a) Plane mirror (b) Incident ray (c) Reflected ray (d) Point of incidence (e) Normal (f) Angle of incidence (e) Angle of reflection.

2. How many reflected rays can there be for a given single incident ray falling on a plane mirror?

3. State the Laws of Reflection of Light.

4. An incident ray makes an angle of 75 with the surface of a plane mirror. What will be the angle of reflection?

5 A ray of light is incident normally {perpendicularly} on a plane mirror. Where will this ray of light go after reflection from the mirror?

6 What is the difference between regular reflection and diffuse reflection of light?

7 State whether the following statement is true or false : Diffuse reflection means the failure of the laws of reflection of light.

8 Draw a labeled diagram showing how a plane mirror forms an image of a point object placed in front of it.

9 If an object is placed at a distance of 7.5 cm from a plane mirror, how far would it be from its image?

10 You see your image in a plane mirror? State two characteristics of the image so f o r m e d.

11 Name the phenomenon responsible for the following effect: When we sit in front of a plane mirror and write with our right hand, it appears in the mirror that we are writing with the left hand.

12 Fill in the following blanks: If you touch your------ ear with right hand in front of a plane mirror, it will be seen in the mirror that your right ear is touched with -------

13 How are the two plane mirrors in a periscope arranged? With respect to one another? With respect to sides of the tube?

14 Explain how, a hair dresser makes you see hair at the back of your head after the hair cut is complete.

15 How many images of an object will be formed when the object is placed between two plane mirrors which are inclined at the following angles to one another?{a} 120

{b} 45

{c} 180

{d} 60

{e} 90

16 What will be the number of images formed when an object is placed between two parallel plane mirrors facing each other?

17 Describe the construction of a kaleidoscope.

18 How many plane mirror strips are there in a kaleidoscope? How are they arranged?

19 State one use of kaleidoscope.

20 What is meant by “dispersion of light “? Name a natural phenomenon which is caused by the dispersion of sunlight in the sky.

21.What are the functions of the following parts of the eye?

(a) Iris (b) Ciliary muscles (c) Retina (d) optic nerve.

22.Give reasons for the followinga) A shiny metal utensil forms an image, but the image is not clear as that formed by a mirror.

b) You see a clear, bright image of an object in a mirror.

c ) When a mirror is held behind your head after a haircut, not only you see the back of your head, you also see innumerable images of yourself. 23.Answer the following in not more than 20 words.

b. What happens to the rays of light in case of diffuse reflection? c . An object is placed 20 cm in front of a plane mirror. Where is the image formed? How far is it from the mirror?

24. Answer the following in not more than 100 words. a. What vision related problems occur when the diet lacks Vitamin A? b. Describe the structure of the eye with the help of a diagram.

25.Name the form o f energy which enables us to see the objects?

26.What types of waves are light waves?

27.Define a ray of light.

52.How do we see objects?

49.Give any three phenomena shown by light.

64.Why the world AMBULANCE is written as its mirror image in front of the hospital vans?

65.What doy ou mean by lateral inversion?66.Draw a neat and labeled diagram o f human eye.

44.Define a beam o f light?

45.Give an example of be s t reflector of light.

46.What type of image is formed in a plane mirror?

OBJECTIVE1.Light is a form of ___________ radiation.(A) Electromagnetic. B) Mechanical. (C) Longitudinal. (D) None o f these.

3.An ________ image canbe obtained o n a screen.(A) Real . (B) Virtual. (C) Upright. (D) Inverted.

4.According to the laws of reflection:(A) Angle i = Angle r (B) Angle i not equal to Angle r (C) ) Angle i = Normal (D) All o f these.

5.T h e colour of an object is determined by(A) T h e colour o f light reflected by it: (B) The colour of light absorbed by it.(C) The colour o f light incident on it o n l y . (D) None o f the above.

6.Human eye is one o f the most valuable and sensitive organ that:(A) Enables us to see the wonderful world a n d colours around us.(B) Can identify the objects.(C) Is like a camera.(D) All o f these.

7.T h e ray of light strikes at the surface o f mirror is called:(A) Reflected ray.(B) Incident ray.(C) Normal ray.(D) None o f these.

8.Wh i c h of the following does not describe working of the human eye?(A) Light enters the eye through a thin membrane called the cornea.(B) Rainbow is formeddue to splitting of whi te light.(C) Iri s is a dark mus cul ar diaphragm that controls the size of the pupil for.(D) Regulating the amount o f light entering into the e y e .

9.E l e c t r i c a l signals generated by light sensitive cells o f retina a r e sent to the brain via:(A) Mo t o r nerves.(B) Optic nerves.(C) Sensory nerves.(D) Spinal cord.

10.The eye lensforms an ___________ and _________ image of the object on the retina.(A) Virtual and erect.(B) Real and inve r t e d .

(C) Real and erect.(D) Virtual and e r e c t .

11.The transparent front part of eye is called:(A) Iris.(B) Cornea.(C) Pupil.(D) Cone.

12.Reflection froma rough surface is called:(A) Regul ar reflection.(B) Diffused reflection.(C) Irregular reflection.(D) Only (b) & (c).

13.If angl e o f incidence is 3 0than angle of reflection will be(A) 6 0(B) 0(C) 30(D) None.

14.If the angle between incident and reflected ray is 5 0(A) 5 0(B) 30(C) 25(D) 100than find the angle of incidence.

15.Splitting o f whi te light on passage through a triangular prism:(A) Takes place due to the inclined surfaces.(B) Is known a s dispersion o f light.(C) Is into a band o f seven colours known as spectrum.(D) All o f these.

16.What is the angle o f incidence of a ray if the reflected ray is at a n angle of 90° to theincident ray?(A) 5 0(B) 60(C) 45(D) 90

17.The image formed by pl a n e mi r r or is:(A) E r e c t .(B) Upsi de.

(C) Real.(D) All o f these.

18.The size of image formed by the plane mirror is………….the size of object.(A) smaller than(B) bigger than(C) equal to(D) None.

19.Splitting o f whi te light into sevencolours is known as:(A) Dispersion.(B) Reflection.(C) Refraction.(D) None o f these.

20.The angle between reflected rayand normal is known as:(A) angle of reflection.(B) angl e of incidence.(C) angle of refraction.(D) None o f these.

21.The line at right angle to the mi r r or surface at the point o f incidence is called:(A) Incidence ray.(B) Reflected ray.(C) Normal.(D) None.

22.If an object is placed at a distance of 8 cm in front of a plane mirror, howfar its image wi l lformfromthe mirror?(A) 1 6 cm.(B) 8 cm.(C) 4 cm.(D) 10 cm.

23.An o b j e c t 5 cmhi g h is placed in front o f a plane mirror. What is the size of the imageformed?(A) 2 . 5 cm.(B) 10 cm.(C) 5 cm.(D) None o f these.

24.Whi ch types of c e l l s present on retinarespond to the intensity of light?(A) Cones .(B) Rods.(C) Both.(D) None.

25.Whi ch types of c e l l s present on retinarespond to the colours?(A) Cones .(B) Rods.(C) Both.(D) None.

26.The human eye forms the image o f an o b j e c t at its:(A) Cornea.(B) Iris.(C) Pupil.D) Retina.

27.The part o f e y e , whi ch is equivalent to the photographic filmin a came(A) Cor nea.(B) Iris.(C) Pupil.D) Retina.

28.The part, which controls the amount of light entering the eye, is(A) Cor nea.(B) Iris.(C) Pupil.D) Retina.

29.The image, which canbe obtained o n a screen is called:(A) Real .(B) Virtual.(C) Upsi de.(D) None.

1. Use these words : absorbs, refraction, reflected, energy, wavelengths, prism, colours

Light is a form of ___________ that mostly behaves like a wave.

White light is made up of different _______________. Different wavelengths give different ___________.

You can see the different colours of the rainbow when light passes through water droplets or a glass triangular __________. The different wavelengths bend differently through the water or the glass, which separates the colours. This is called ______________. Colour the diagram!

2. You see different colours

according to the wavelengths of light that are absorbed or _____________ from the object you are looking at. For example, a ripe tomato looks red because it reflects the red wavelength of light back to your eyes and __________ the other colours.

3. Match the sentence halves by drawing a line between them.

a A rainbow is made when • the least when passing through the prism.

b Red light bends • it absorbs all light wavelengths except green.

c Violet light bends • light passes through water droplets and refracts into its different wavelengths.

d A lemon looks yellow because • the most when passing through the prism.

e Grass looks green because • it reflects the yellow light back to our eyes.

The surface of the apple is reflecting the wavelengths we see as red and absorbing all the rest. An object appears white when it reflects all wavelengths and black when it absorbs them all.

Red, green and blue are the additive primary colours of the colour spectrum. Combining balanced amounts of red, green and blue lights also produces pure white. By varying the amount of red, green and blue light, all of the colours in the visible spectrum can be produced.

4. A white box of photographic paper has been written on in large red letters. The box of paper is in a photographic darkroom where the only light is from a RED lamp.

a) What colour does the white box appear

b) What colour does the red writing appear

c) The red lamp is now switched off and a green lamp is switched on.

(i)What colour does the red writing appear in the green light?

(ii)Explain why the writing will appear this colour?

5. Name that process that split the white light into different colour. Write down the names of the seven colours of a rainbow, in the right order.

6. When white light is passed through a prism, which colour of light is refracted the most?

7. When you shine white light into a blue filter:

(a) which colour passes through the filter?

(b) what happens to the other colours?

8. In terms of the light falling on it;

(a) why is this ink black?

(b) why is the paper white?Reflection and Mirrors

When light strikes a surface it is reflected. The light ray striking the surface is called the incident ray. A normal (perpendicular) line is then drawn at the point where the light strikes the surface. The angle between the incident ray and the normal is called the angle of incidence. The light is then reflected so that the angle of incidence is equal to the angle of reflection. The angle of reflection is the angle between the normal and the reflected light ray. The incident ray, normal, and reflected ray are all in the same plane. The law of reflections states that the angle of incidence is equal to the angle of reflection.

Incident RayAngle of Incidence

Reflected Ray

Angle of Reflection

Mirror

Normal

The law of reflection holds true for any type of surface. Specular or regular reflection occurs when light is reflected from a smooth surface. When parallel light rays strike a smooth surface they are reflected and will still be parallel to each other. If they are parallel to each other, they will all have the same angle of incidence and therefore, the same angle of reflection.

Diffuse reflection occurs when light is reflected from a rough surface. The word rough is a relative term. The surface can be rough at a microscopic level, for example, an egg is a rough surface. When parallel light rays strike a rough surface, the light rays are reflected in all directions according to the law of reflection. Since the surface is rough, the parallel light rays will strike the surface with different angles of incidence and therefore they will not all have the same angle of reflection.

Plane Mirrors have a flat surface. The mirror hanging on the wall in your bathroom is a plane mirror.

In a plane mirror the object is the same size, upright, and the same distance behind the mirror as the object is in front of the mirror. Images in a plane mirror are also reversed left to right.

Convex

Concave

Real images are images that form where light rays actually cross. In the case of mirrors, that means they form on the same side of the mirror as the object since light can not pass through a mirror. Real images are always inverted (flipped upside down).

Virtual images are images that form where light rays appear to have crossed. In the case of mirrors, that means they form behind the mirror. Virtual images are always upright.

Convex mirrors are made from a section of a sphere whose outer surface was reflective. Convex mirrors are also known as diverging mirrors since they spread out light rays. They are typically found as store security mirrors.

Concave mirrors are made from a section of a sphere whose inner surface was reflective. Concave mirrors are also known as converging mirrors since they bring light rays to a focus. They are typically found as magnifying mirrors

The distance from the center of curvature to the mirror is called the radius of curvature (C). The center of curvature of a curved mirror is located at the center of the sphere from which it was made. The focal point is located halfway between the mirror’s surface and the center of curvature. The focal length is the distance from the focal point to the mirror along the principle axis. The principle axis is a line that passes through both the center of curvature (C) and the focal point (f) and intersects the mirror at a right angle.

Answer the following questions:1. What is the meaning of “Reflection”?

2. What is the Law of Reflection?

3. What is the Normal?

4. What are the main differences between Regular and Diffused Reflection?

5. How can you tell whether the image is real or virtual?

6. What is the difference between Inverted image and Laterally inverted image? Which type of mirror will form each type of image?

7. What is another term for a convex mirror? What is the meaning of this term? Use a diagram to represent it.

8. What sort of image does a convex mirror form?

9. Give 3 applications or uses of convex mirror.

10. A Concave mirror can form 2 types of images: describe each of this image formed.(1) When it is very close to the object -

(2) When it is far away -

11. Complete the drawing of a concave and a parabolic mirror.

12. Give 3 applications or uses of concave mirror.

Section A—Multiple choice

1 Light travels with a speed at aboutA. 300,000 meters per second B. 3,000,000 meters per secondC. 30,000 kilometres per second D. 300,000 kilometres per second 1

2 i) Which of the Electromagnetic radiation (EMR) has the highest frequency?A infrared light B radio wavesC X-rays D microwaves 1

3 Which of the following waves does not belong to electromagnetic radiation?A infrared light B white lightC X-rays D sound waves 1

4 Which of the radiation is involved in scanning luggage at the airport?A X-rays B microwaves C gamma rays D blue light 1

5 Blue skies and red sunsets are caused by the:A dispersion of light B refraction of lightC absorption of light D scattering of light 1

6 i) Comparing microwaves and ultraviolet rays,ii) A microwaves have lower frequenciesiii) B ultraviolet rays have longer wavelengthsiv) C microwaves have more energy than ultraviolet raysv) D ultraviolet rays are more visible than microwaves 1

7 The law of reflection isA the angle of incidence equals the angle of reflectionB the angle of incidence is greater than the angle of reflectionC the angle of incidence is less than the angle of reflectionD the angle of incidence does not equal the angle of reflection

8 Three primary colours of light which mix to make white light, they are:A yellow, green, red B cyan, yellow, magentaC green, blue, red D red, green, orange 1

Section B—Written answers (60 marks)

1 If a light ray strikes a mirror at an angle of 30o to the mirror, what is:a the angle of incidence?b the angle of reflection?

ab

2

2 What is meant by the refraction of light?

2

3 The diagram on the right shows a light ray travelling through air to the interface between the air and a glass block.

On the diagram, draw the normal, and a possible path for the ray in the glass.

Label on the diagram: normal, angle of incidence, angle of refraction, refracted ray, incident ray

4

4 Curved mirrors are usually shown in cross-sectional views to indicate their shapes. Three such shapes are shown below.

a Which mirror is which?(parabolic, convex, concave )

b What happen when a spot light is placed in front of each of these mirrors?

c Give one use of each of these mirrors. 9

5 Is light always refracted when it passes from one material to another? Explain your answer. 2

6 a When do people use infrared camera or binoculars work?

b How does infrared camera work?

3

7 Explain why the sky appears blue during the day.

2

8 Complete the following table on EMR.

Radiation Special Feature Uses

microwave

just beyond the visible spectrum

radiowaves

shortest wavelength and the most powerful energy

visible

Using the following:telecommunication, ultraviolet, cancer treatment, photosynthesis, cooking, longest wavelength and lowest frequency, only spectrum visible to human eye, wavelengths ranging from 1 mm to 1 m, sun tanning, gamma ray 10