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Chung Cheng High School ( Main)

Sec 1 Physics Chapter E3

Name:__________________ ( ) Class :______ Date :_________

What is Light?

Definition:

Light is a form of energy that enables us to see things around us when it

enters our eyes.

Properties of Light1. It is a form of energy

2. made of seven different coloured waves mixed uniformly to form white light

3. travels in straight lines called rays

4. a bundle of light rays is called a beam

5. Travels at a speed of 300000000 m/s in a vacuum

What is Reflection?

Definition:

The image in a mirror is formed when light rays bounce off the mirror and travel to your

eyes. This bouncing of light off a mirror is called reflection.

X Y

BA

Nincident ray

Plane mirror

Normal

angle on incidence

Angle of reflection

reflected ray

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Laws of Reflection

1. 1st Law of Reflection: Angle of incidence is equal to the angle of reflection

2. 2nd Law of Reflection: Incident ray, reflected ray and normal ,at the point of

incidence, lie on the same plane.

Characteristics of an Image

1. the image is upright

2. of the same size as the object;

3. the image lies far behind the mirror as the object is in front of the mirror;

4. the image is laterally inverted;

5. the image formed is always a virtual image.

Examples of Virtual Images:

Images seen in the mirror, on still water or any reflecting surface.

Ray diagrams

Q1

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Q2

Q3

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Difference between real and virtual image

Virtual image Real Image

Formed by mental extension of rays Formed by converging rays

Cannot be projected on a screen Can be projected on a screen

Not inverted Inverted

Examples of Real Images:

Images captured on the retina of the eye, a photograph, on screen using a projector or

visualiser

Uses of mirrors

Type of mirrors Plane mirror Convex mirror Concave mirror

Is the imageObject near

mirror

Object far from

mirror

real or virtual? Virtual Virtual Virtual real

upright or inverted? upright upright upright inverted

same size, magnified

or smaller ?same smaller magnified smaller

Uses

Periscope,

Dressing table

mirrors

Blindspot mirrors,

security mirrors

Cosmetic

mirrors, dentist

mirrors

Spectacles lens

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Practice Questions 1

1. We are able to see non-luminous objects because .

A) They reflect light into our eyes

B) Light passes straight through them

C) They give off visible light

D) Light from our eyes can reach them ( A 2. Which of the following statements is true?

A) Light is a form of energy. YES

B) Light travels at a speed of 3.0 x 107 m/s wrong

C) The sun and moon are our main sources of light wrong

D) Light cannot travel in a vacuum wrong ( A

3. Which one of the following best describe the image we would see when we look at

a plane mirror?

A) Inverted and same size

B) Inverted and smaller size

C) Upright and smaller size

D) Upright and same size ( D

4. Consider the diagram below

i. Which one of the angles (A, B, C, or D) is the angle of incidence?

ii. Which one of the angles is the angle of reflection?

( B )

( C )

5. A ray of light is incident towards a plane mirror at an angle of 30-degrees with the

mirror surface. What will be the angle of reflection? Show your working.

Since angle of reflection = angle of incidence,

Angle of reflection is = 90 30 60

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6. Draw the correct rays of light to demonstrate how a virtual image is formed.


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9. A ray of light is approaching a set of three mirrors as shown in the diagram. The light

ray is approaching the first mirror at an angle of 45-degrees with the mirror surface.

a) Trace the path of the light ray as it bounces off the mirror; continue tracing the

ray until it finally exits from the mirror system. Label the normals, angles of

incidence and reflection.

b) How many times will the ray reflect before it finally exits?

No. of times :_2____

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10. Is it easier to read from pages of a book which are rough or from pages which are

smooth and glossy? Explain your answer.

It is much easier to read from rough pages which provide for diffused reflection.

Glossy pages result in regular reflection and cause a glare. The reader typically sees

an image of the light bulb which illuminates the page.

11. The reflection of the mountains can be seen in a lake when it is calm, but cannot be

seen when the wind blows across it.

When the sea is calm, the surface of the sea is smooth and even, thus regular

reflection occurs, allowing the image to be formed.

When the winds blow, the surface of the lake becomes rough and diffused

reflection occurs. Thus no image is seen.

12. A boy is having his eyesight tested by an optician. The chart is located 5.0m behindhim. There is a mirror 4.0m in front of him. How far does this chart appears from him?

Dist = 9 + 4 =13m

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What is Refraction?

Definition:

Refraction is the bending of light when it enters into another medium of different optical density.

When light travels from air to glass, it is travelling into anoptically denser medium. The speed of light decreases.The light ray bends towards the normal.

When light travels from glassto air, it is travelling into anoptically less dense medium.

The speed of light increases.

The light ray bends away from the normal.

When the incident ray is perpendicular to boundary surface, it will travel without any deviation

from its original path.

Effects of Refraction

The bending of light causes an object to appear nearer than it actually is.

Complete the ray diagrams below by drawing the path of 2 light rays they passes throughdifferent medium to reach the eye.

Q1 A man in air looking at the fish in the water.

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Q2 A person look directly at a ball in the water.

Q3 A fish in water looking at a dragonfly in the air.

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1. Refraction occurs when light passes from one transparent medium toanother. This is due to

A) the color of the mediumB) the change in the speed of lightC) the absorption of light

D) the light being partially reflected ( B )

2. When a light ray travels from a more dense, transparent medium to a lessdenser, transparent medium at an angle, it __________________.

A) slows down and bends away from the normalB) travels at the same speed but bends towards the normalC) increases in speed and bends away from the normalD) increases in speed down and bends towards the normal ( C )

3. Light travels at different speeds in different mediums, which is the correct

order of decreasing speed of light in the following materials?

A) Air, glass, waterB) Water, glass, airC) Air, water, glassD) glass, water, air

( C )4. Light is not refracted when it passes

A) from glass to waterB) from air to oilC) from hot air to cold air

D) through 2 liquids of same density( D )

5. The following phenomena are the result of refraction except _________.

A) the formation of mirageB) a spoon partially in water appears bentC) the apparent depth of the swimming pool appears shallower than actual

its depthD) the formation of images by convex mirrors

( D )6. A ray of light falls on a rectangular glass block. The light ray is refracted as

shown. Which diagram shows the correct path of light?

( a ) ( b ) ( c ) ( d )( A )

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B

D

7. A girl looks directly down at a fish at the bottom of a transparent fish tank. Atwhich position A, B,C, D will the fish appear to be?

( A )8. Which of the following statement about refraction is true?

A) the incident beam, refracted beam and the normal lie on the same planeB) refraction is always due to light slowing downC) the angle of incidence is always equal to angle of refractionD) the incident ray and refracted ray are in the same medium

( A )

9. A ray of light passes from water to air. Which labeled arrow shows the

direction of the ray in air?

( D )10. Complete the diagram below to show the behavior of a light ray traveling

from water into air. Label your angle of incidence i, angle of refraction r, andthe normal N.

A

C

D

water

air

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11. The figure shows a ray of light passing from material A to material B. If oneof the medium is water and the other is glass, identify A and B. ( speed oflight is slower in glass than in water)

12. Complete the diagrams below by drawing the path of a light ray as it entersand leaves each medium

13. Complete the ray diagrams below by drawing the path of 2 light rays theypasses through different medium to reach the eye.

a )

Water

A : Glass_

B : Water

glass blockb )a ) glass prism

c )

air

water

glass

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b )

c )

Water

Air

Eye

CoinWater

Air

Eye

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Spectrum of white light.

Definition:

Dispersion is the process where white light is spilt into its component colours

White light is a mixture of seven different colours called a spectrum.

When the incident beam of white light enters into the prism, it splits up and disperses into aspectrum.

The spectrum of white light consists of seven colours: red, orange, yellow, green, blue, indigoand violet.

These component colours are refracted towards the normal at different angles.

Violet light slows down the most while red light slows down the least. Hence, violet light bendsmore than red light during refraction.

When they emerged from the prism, they are again refracted by different amount. A continuousspectrum of different colours overlapping at the edges is seen on the screen.

The colours of the spectrum can be recombined to give white light again by using a 2 nd prism.

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1. Which of the following terms describe the process in which white light is split intoits component colours?

A) Absorption

B) Reflection

C) Dispersion

D) Refraction

( B

2. A narrow beam of white light is passed through a glass prism. Which of thefollowing is correct about the spectrum formed?

X Y ZA) Violet Green BlueB) Indigo Orange VioletC) Violet Blue Red

D) Red Yellow Green ( C

3. A rainbow is formed as a result of theA) absorption of sunlight by raindropsB) dispersion of sunlight by raindropsC) scattering of sunlight by the atmosphereD) reflection of sunlight by the raindrops

( B

4. Two lights of different color are shone through a piece of glass. From thediagrams below, identify the most possible set of colors that are being used.

Light A Light B

A) Red GreenB) Blue YellowC) Orange IndigoD) Green Violet

( B

Z

Y

X

Light ALight B

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