S1SC - Chapter 8 Light and Optics

S1SC - Chapter 8 Light and Optics

by Teacher Susan

​8.1 Uses of Mirrors

​Real image and virtual image

• ​Image - true impression of an object that can be seen by our eyes.

• ​Two types of images

  • ​real image

  • ​virtual image

​8.1 Uses of Mirrors

Characteristics of images formed by plane mirror, concave mirror and convex mirror​

​Plane mirror

• ​has a flat surface

• ​characteristics of image formed:

  • ​virtual

  • ​upright

  • ​same size as the object

  • ​laterally inverted

  • ​distance between object and mirror (u) = distance between image and mirror (v)

​8.1 Uses of Mirrors

Characteristics of images formed by plane mirror, concave mirror and convex mirror​

The linear distance of image and object

= distance of image + distance of object

​

​Example 1

​Karim stands 40 cm in front of the mirror. Calculate the distance X.

​8.1 Uses of Mirrors

Characteristics of images formed by plane mirror, concave mirror and convex mirror​

​

​Example 2

A ball is 15 cm in front of a plane mirror. Then, this mirror is moved 5 cm to position X. What is the distance between the new image and the ball?

​8.1 Uses of Mirrors

Characteristics of images formed by plane mirror, concave mirror and convex mirror​

​

​Example 3

​A cat is 5 m from the image of a mouse. If the image of the mouse from the mirror is 1 m, calculate the distance of the cat from the mouse.

Now check your understanding...​

​Activity 8.1a

Multiple Choice

Helena stands 150 cm from a plane mirror. Then, she withdraws 20 cm further from the mirror. What is the distance between Helena and her image?

• 150 cm

• 170 cm

• 320 cm

• 340 cm

​8.1 Uses of Mirrors

Characteristics of images formed by plane mirror, concave mirror and convex mirror​

​Concave mirror

• ​curves inward

• light rays converge at the focal point

• ​characteristics of image formed:

  • ​virtual

  • ​upright

  • ​magnified

​8.1 Uses of Mirrors

Characteristics of images formed by plane mirror, concave mirror and convex mirror​

​Convex mirror

• ​curves outward

• ​characteristics of image formed:

  • ​virtual

  • ​upright

  • ​diminished

​8.1 Uses of Mirrors

Applications of plane mirrors

• ​Reflection of light - when light strikes the surface of a plane mirror, the light rays are reflected/bounced back.

​8.1 Uses of Mirrors

Applications of concave mirrors

• ​can reflect and converge parallel light rays.

​8.1 Uses of Mirrors

Applications of convex mirrors

• ​diverge (spread out) light rays, increasing the field of view.

​8.1 Uses of Mirrors

Optical instruments to enhance our sense of sight

1. ​Periscopes

• ​enable us to see objects behind obstacles

• ​Example: submarines

• ​Structures:

  • ​Two pieces of plane mirrors are arranged in parallel to each other at a 45^o angle.

  • ​The reflective surfaces of both the mirrors face each other.

  • ​The light from the object enters the top opening and is reflected from the top mirror to the bottom mirror.

  • ​Then the light is reflected on the bottom mirror to the observer's eye.

​8.1 Uses of Mirrors

Optical instruments to enhance our sense of sight

1. ​Periscopes

• ​Characteristics of images formed:

  • ​virtual

  • ​upright

  • ​not laterally inverted because the light is reflected twice

  • ​same size as the object

​8.1 Uses of Mirrors

Optical instruments to enhance our sense of sight

2. Kaleidoscopes

• ​use the principle of light reflection to produce attractive patterns

• ​Example: used by fabric designers and visual artists to gain inspiration

• ​Structures:

  • ​Three pieces of plane mirrors are arranged at an angle of 60^o in a tube.

  • ​All the reflective surfaces of the mirrors face inward.

  • ​The mirrors reflect the colourful objects repeatedly to produce amazing patterns.

​8.1 Uses of Mirrors

Optical instruments to enhance our sense of sight

2. Kaleidoscopes

• ​Characteristics of images formed:

  • ​virtual

  • ​upright

  • ​same size as the object

Now check your understanding...​

​Activity 8.1

Multiple Choice

Choose the picture showing the correct ray diagram in a periscope.

​8.2 Properties of Light

• ​Light is a form of energy which travels in the form of waves.

Now check your understanding...​

​Activity 8.2

Fill in the Blank

Light travels in s_______ l____.

Fill in the Blank

Light travels much faster than s____. Thunder and lightning begin at the same time, but we will see the lightning first. When a pistol is fired, we will see the smoke first and then hear the bang.

Fill in the Blank

We can see things around us because they r______ light into our eyes.

Fill in the Blank

S_____ is formed when light is blocked by an object.

​8.3 Reflection of Light

The formation of images on the plane mirror is due to the reflection of light.​

• 1. ​incident ray - the ray that is directed to the mirror.

• ​2. reflected ray - the ray that is reflected from the mirror

  3. normal - the straight line that meets the incident ray and the reflected ray on the mirror surface at a right angle.

• ​4. angle of incidence, i - the angle between the incident ray and the normal.

• 5. angle of reflection, r - the angle betwen the reflected ray and the normal

​8.3 Reflection of Light

​Ray diagrams for the reflection of light

Now check your understanding...​

​Activity 8.3

Multiple Select

A flower pot is placed at point O, in front of a plane mirror. Patricia stands at the points P, Q, R, and S. At which two locations can Patricia see the images of the pot in the mirror?

• P

• Q

• R

• S

​8.3 Reflection of Light

​Applications of reflection of light

• ​improve road safety

• ​reflect light and heat from the sun

​8.4 Refraction of Light

​Definition of refraction of light

• ​bending of light rays when they move through mediums of different densities

• ​occurs due to the changes of speed of light when passing from one medium to another

• ​Light moves at its fastest speed in a vaccum (300 000 km per second)

• ​The speed of light decreases as it moves through air (gas), water (liquid) or a glass block (solid).

​8.4 Refraction of Light

​Ray diagrams to show the refraction of light

​

​https://www.youtube.com/watch?v=_CT-wAIfOYQ

​8.4 Refraction of Light

​Relationship between the incident ray and the refracted ray

• ​The angle of incident, i is the angle between the incident ray and the normal.

• ​The angle of refraction, r is the angle between the refracted ray and the normal.

• ​

​8.4 Refraction of Light

​Application of refraction of light

Now check your understanding...​

​Activity 8.4

Fill in the Blank

When light passes between materials of different __________, it changes direction.

Fill in the Blank

This phenomenon is known as __________.

Fill in the Blank

This happens because the _________ of the light ray changes.

Fill in the Blank

This is why when you look into a swimming pool, it looks __________ than it actually is.

Multiple Choice

The diagram shows a ray of light travelling through air and reaching the surface of water.

Which ray shows the path taken by the light in the water?

• A

• B

• C

• Dj

Multiple Choice

Light travelling through glass will be refracted more than light travelling through water.

Why is this?

• Glass is heavier than water.

• Glass is denser than water.

• Water is clearer than glass.

• Light travel faster in glass.

​8.5 Dispersion of Light

• ​is the separation of white light into a spectrum of lights which has seven colours:

  • ​Red

  • ​Orange

  • ​Yellow

  • ​Green

  • ​Blue

  • ​Indigo

  • ​Violet

​8.5 Dispersion of Light

• When passing through a medium like glass, the white light is refracted and separated into seven colour components which are arranged in a particular order.

• ​This is because each light component moves through the medium at different speeds → different angles of refraction, r

• Red light: fastest speed, smallest angle of refraction, nearest to the normal

• Violet light: slowest speed, biggest angle of refraction, furthest from the normal

​8.5 Dispersion of Light

• When the ray box is switched on, the white light ray is directed obliquely at the glass prism.

• ​The white light is refracted and separated by the glass prism into the seven components of coloured lights.

• ​Each colour is refracted at a different angle with the red colour refracted the least and the violet colour refracted the most.

​https://www.youtube.com/watch?v=--b1F6jUx44

Now check your understanding...​

​Activity 8.5a

Multiple Choice

Oliver transmitted a beam of white light into a glass prism. The whilte light is dispersed into a spectrum of light arranged in the order as shown in the diagram.

This happens because each coloured light moves at a different speed.

• True

• False

Multiple Choice

This happens because each coloured light is refracted at a different angle.

• True

• False

Multiple Choice

This happens because violet and red coloured lights move at the same speed.

• True

• False

Multiple Choice

This happens because green coloured light has the lowest speed.

• True

• False

​8.5 Dispersion of Light

​Dispersion of light in daily life

• ​A rainbow is a natural phenomenon which can be seen in the sky after the rain.

• ​A rainbow is a spectrum of light formed in the sky.

• ​The water droplets suspended in the air act as prisms that disperse the white sunlight into the seven colours of the rainbow.

Now check your understanding...​

​Activity 8.5

Multiple Select

Choose the correct statements about the formation of rainbows.

• The formation of rainbows require water droplets and sunlight.

• A rainbow produces eight different coloured lights.

• A rainbow is formed through the dispersion of light.

• Rainbows are produced by the reflection of light on the surface of the water droplets.

​8.6 Scattering of Light

• ​The atmosphere of the Earth contains fine suspended particles such as gas, water vapour, and dust.

• ​When the sunlight penetrates the atmosphere and reach these particles, the light is reflected in many directions.

• ​The scattering of light is the process whereby light is reflected and transmitted in all directions by the fine particles in the air.

• ​

​https://www.youtube.com/watch?v=2zcKdlzxFzw

​8.6 Scattering of Light

​Scattering of light in daily life

1.The blue sky

- During daytime, the Sun is vertically above us in the sky.

​- The sunlight penetrates the thin atmospheric layer before reaching the Earth.

​- Violet light is scattered the most

​- Red light is scattered the least.

​- Our eyes are more sensitive to blue light. Hence, sky appears blue during daytime.

​8.6 Scattering of Light

​Scattering of light in daily life

2.The red sunrise and sunset

​- During dawn and dusk, the Sun is low on the horizon of the Sky.

​- Sunlight penetrates the thick atmospheric layer before reaching the Earth.

​- The scattered violet, indigo, blue, and green light disappear from the original pathway of the light.

​- The sky and the Sun appear reddish.

​- The Sun is redder if the air is polluted because of the large amount of dust particles present in the air.

Now check your understanding...​

​Activity 8.6

Multiple Choice

Choose the correct statement that explains the phenomenon of the blue sky.

• The cloud reflects the blue light.

• The blueness of the sea is reflected to the sky.

• Sunlight transmits more blue light.

• Blue light is scattered by the particles in the atmosphere.

​8.7 Addition and Subtraction of Light

Addition of light​

• ​The primary colours are the basic colours.

• ​They cannot be obtained by mixing other colours.

​8.7 Addition and Subtraction of Light

Addition of light​

• Secondary colours are obtained from the addition of two primary colours.

• ​They are cyan, magenta, and yellow.

• ​The addition of all the primary colours OR all the secondary colours will produce white light.

Now check your understanding...​

​Activity 8.7a

Multiple Choice

Alisha shines two spots of primary coloured lights P and Q on a white screen to form an overlapping area X.

Which is the result of colour X from the addition of:

P- Green, Q - Red

• Yellow

• Blue

• Magenta

Multiple Choice

Which is the result of colour P from the addition of:

Q - Red, X - Magenta

• Cyan

• Blue

• Yellow

Multiple Choice

Which is the result of colour Q from the addition of:

P - Blue, X - Cyan

• Magenta

• Yellow

• Green

​8.7 Addition and Subtraction of Light

Subtraction of light​

• ​A colour filter is a transparent material that only allows a specific coloured light to pass through it.

• ​The other colours are absorbed which is called the subtraction of light.

• ​There are two types of colour filters:

  • ​Primary colour filter

  • ​Secondary colour filter

​8.7 Addition and Subtraction of Light

Subtraction of light

• ​Primary colour filter

  • ​only allows its own colour to pass through it.

  • ​The other colours are absorbed.

​8.7 Addition and Subtraction of Light

Subtraction of light

• Secondary colour filter

  • ​only allows its own colour and the colours that form it to pass through.

  • ​The other colours are absorbed.

​8.7 Addition and Subtraction of Light

Principle of light subtraction

• ​enables us to see coloured objects in white light.

• ​When white light shines on coloured object, some of the light of its colour components are absorbed while others are reflected.

• ​The colour absorbed are subtracted from white light.

• ​The colours that are not absorbed are reflected into our eyes, giving the object its colour.

​8.7 Addition and Subtraction of Light

​Differences between the addition and subtraction of light

​8.7 Addition and Subtraction of Light

Addition and subtraction of light in daily life

Now check your understanding...​

​Activity 8.7b

Multiple Choice

Safina shines a beam of white light to a white screen. She then placed a yellow filter and a magenta filter in front of the screen.

What colour is the light formed on the screen?

• Blue

• Red

• Yellow

• Cyan