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CHAPTER 7 LIGHT, COLOUR AND SIGHT

7.1 Synthesising the formation of image by plane mirrors and lenses

7.2 Synthesising the formation of image by optical instruments

7.3 Analysing light dispersion7.4 Analysing light scattering7.5 Analysing the addition and subtraction of coloured lights7.6 Applying the principle of subtraction of coloured light to

explain the appearance of coloured objects7.7 Analysing the effect of mixing pigments7.8 Evaluating the importance of colour in daily life7.9 Appreciating the benefits of various types of optical

instruments to mankind

7.1 Synthesising the formation of image by plane mirrors and lenses

Formation of an Image by a Plane Mirror1. The image of an object is formed because of the ___________________________________2. An image formed by a plane mirror is caused by the ______________________ from the

surface of the mirror.

3. When you are looking at yourself in a plane mirror, your face is the object, the light rays from

the object (your face) are reflected by the plane mirror to your eyes.

Characteristics of an Image Formed by a Plane Mirror

1. The image is _________________________________________________________________

2. The image is _________________________________________________________________

3. The image has the _____________________________________________________________

4. The image formed is ___________________________________________________________

____________________________________________________________________________

5. ____________________________________________________________________________

____________________________________________________________________________

Characteristics of an Image Formed by Lenses

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7.2 Synthesising the formation of image by optical instruments

Pin-hole Camera1. The pin-hole camera consists of a sealed closed box which has _______________ on one

end and a _____________________________ on the other end.

2. An object is placed in front of the camera so that the light rays can enter through the pin-hole

and form an image on the surface of the screen.

3. The image formed is real, inverted and smaller than the object.

4. To get a sharp image, the pin-hole must be _______________5. If more than one hole is made___________________________________________________

___________________________________________________________________________6. The table below shows images formed by pin-holes of different sizes.

Condition Characteristic of the image

The object is placed closer to the pinhole

The object is placed further away from the pinholeThe pinhole is made smaller

丁 he pinhole is made biggerA convex lens is placed in front of thecameraThe Human Eye and Camera

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1. Both the human eye and camera use a __________________ for focusing.

2. Images formed in the human eye and the camera are real, inverted and smaller than the

actual size.

3. The focal length of the eye lens can be adjusted to __________________________________4. The ability of the eye lens to change its thickness to focus objects from various distances is

called ________________________________5. The camera lens is unable to change its for focusing on near and distant. Far focusing, the

focusing ring is change the position of the camera lens by moving it nearer or further from the

film.

Function of Human Eye and Camera

Ability of our eye and the camera to focus on a nearby or distant object

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Formation of Image by Optical Instruments

Periscope1. Periscope is used to ________________________

_________________________________________2. Both periscope mirrors are placed at _______ Light

from an object enters the periscope and is reflected into the eye of the observer. The plane mirrors in the periscope can be replaced by _______________________________________________________

Microscope1. Microscope is used to _______________________

_________________________________________2. The microscope uses two convex lenses, the

_________________________________ which have short focus lengths.

3. The focal length of the objective lens is ____________________ the focal length of the eyepiece.

4. The objective lens forms a ___________________________________________________

5. The eyepiece acts as _____________________6. to enlarge image formed by the objective lens. The

final image formed is _________________________________________________________________

Magnifying Glass1. Magnifying glass is used to ___________________2. This type of lens has a ________________ Objects

should be placed at the position _____________ the focal point of the lens.

3. The image formed by a magnifying glass is _________________________________________

Telescope1. Telescope is used to ________________________2. The telescope uses two convex lenses, the

objective lens and eye piece.3. The objective lens has a __________________ The

eye piece has a ______________________4. The objective lens forms a ____________________

________________________________________5. The eye piece acts as a magnifying glass to

magnify the real image formed by the objective lens. The final image formed is _____________________________________________________________

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Exercise 7.2Study the following statement

You are given on thick convex lens, one thin convex lens, a lens holder and a white screen.

(a) Suggest a hypothesis to investigate the above statement.

___________________________________________________________________________ [1 mark]

(b) Describe an experiment to test your hypothesis based on the following criteria.(i) Aim of the experiment [1 mark](ii) Identification of variables [2 marks](iii) List of apparatus and materials [1 mark](iv) Procedure or method [4 marks](v) Tabulation of data [1 mark]

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The focal length of a convex lens depends on the lens thickness.

____________________________________________________________________________

____________________________________________________________________________

7.3 Analysing light dispersion

1. White light is actually made up of ________________________________________________2. The process of separation of white light into seven different colours is called the ___________

_____________________________3. The dispersion of light occurs because the components of white light ____________________

____________________________

4. The dispersion of white light into the seven colours of the spectrum, i.e. ________________________________________occurs when white light passes through a _________________

5. The seven components of white light which move at different speeds are ____________________________________________________

6. Violet light that has the ______________________ is refracted the most, while red light that

has the highest speed is ______________________________________

7. All colours of the spectrum can __________________________________________________

________________________________at the edge of the glass prism as shown Diagram 7.9.

The Formation of Rainbow

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1. A rainbow is a natural phenomenon resulting from ______________________________________________________________________________________________________________

2. The components of different colours in sunlight undergo different amounts of _________________________________________ into seven different colours.

3. The rays of different colours then undergo _______________________________ before they

finally emerge from the water droplets and are observed by us.

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7.4 Analysing light scattering

Light Scattering

1. _____________________________________________ before reaching the Earth's surface.

2. The atmosphere has particles of _________________________________3. When light travels through and strikes these particles, the light gets _____________________

_________________The light is reflected at _______________________________________ This process is known as ________________________________

4. Scattering of light depends on the ____________________ of the colours of light.

5. Red and orange light with _______________________________________________6. ____________________________ with shorter wavelengths are more scattered and

___________________________________________

The Blue Sky Phenomenon1. At noon (daytime), the Sun is ___________________________________2. This results in the sunlight travelling ______________________________________________

_________________________________________________3. This causes the components of light with __________________________________________

___________________________________________________________________________

4. However, the components of light with _______________________ such as blue and violet

light will be ____________________________________________________________________________________________________________

5. Therefore, the sky appears to be ____________

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The Phenomenon of Reddish Sky 1. During sunset, light from the Sun has to travel _____________________________________

_________________________________________________before reaching the Earth.

2. During this time, the components of light with _________________________________________________________________________________________from the Earth.

3. At the same time, the components of light with longer wavelengths such as ________________________________________________________________________________________

4. During sunset, the sky appears to be ____________________ when seen by an observer on

the Earth because there are a lot of _____________________________________________

Blue skies Aspects Red sunsetsDistance travelled by

sunlight to reach the Earth

Layer of atmosphere

particles

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Scattering of light

7.5 Analysing the addition and subtraction of coloured lights

Primary and Secondary Colours1. The colours of the light can be classified into two groups, namely _______________________

_________________________________2. Secondary colours can be obtained by the _______________________________________

3. A mixture of all three primary colours will produce a white colour.

Terms Meanings Colours

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Subtraction of Coloured Lights1. _____________________ can be used to subtract coloured lights.

2. A primary coloured filter only allows _________________________________ Other colours

are ___________________________________________3. A _______________________________________________________________ only allows

____________________________________________________________________Other

colours are absorbed (subtracted).

4. The colour that is being removed from the filter is the ________________________________

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