Light and Shadow class 5 icse

 

Light and Shadow

TRANSPARENT, TRANSLUCENT AND OPAQUE OBJECTS

Do You Know?

Light travels from the Sun to the Earth in about 8 minutes.

When light falls on an object, it gets reflected from the object and enters our eyes to form an image of that object. Some objects allow light to pass through them while some objects do not allow any light to pass through them. Based on these properties, objects are classified as transparent, translucent and opaque.

The objects which allow light to pass through them completely are called transparent objects, for example, clear glass, clean water, air, etc.) etc.)

The objects which allow only some light to pass through them are called translucent objects, for example, dirty water, tracing paper, muslin cloth, frosted glass, etc.

(The objects which do not allow any light to pass through them are called opaque objects, for example, a book, a paper, a duster, a wooden chair, a steel plate, etc.

SHADOWS

While in the playground on a sunny day, we usually take a break under the shade of a tree. The shade of the tree is actually the shadow of the tree.

Shadows are mostly black or grey patches which are formed by objects when light travelling in a straight line is blocked by these objects. However, a shadow can also be colourful depending on the light (source) getting reflected on a surface.

Conditions Required for the Formation of a Shadow

There are three things needed for a shadow to form.

Source of light: A shadow is formed only when light falls on an opaque object.

Opaque or translucent object: Opaque objects form clear shadows while translucent objects form blurry shadows. A screen or a surface for the shadow to form on.

Characteristics of a Shadow

A shadow has the following characteristics:

A shadow is always formed on the opposite side of the source of light. If you are facing the source of light, your shadow will form behind you.

A shadow is mostly black or grey in colour, but this would depend on the object and the colour of the source of light.

A shadow only shows the outline of the object and not the details.

• The size of the shadow depends on two factors:

the distance between the object and the source of light

the distance between the the screen and the object

 

FORMATION OF DAY AND NIGHT

✓

The Earth spins on its axis. This axis is an imaginary line which passes through the Earth from the North pole to the South pole. The spinning of the Earth on its axis is called rotation. The Earth completes one rotation on its axis in approximately 24 hours. This rotation of the Earth on its axis causes day and night. The part of the Earth that faces the Sun has day, and the other part of the Earth observes night.

ECLIPSES

We know that the Earth revolves around the Sun and the Moon revolves around the Earth. During this revolution, the three heavenly bodies sometimes align in a straight line. When this happens, they cast a shadow on each other. For instance, when the Earth comes between the Sun and the Moon, the Earth casts its shadow on the Moon, and when the Moon comes between the Sun and the Earth, the Moon casts its shadow on the Earth. These shadows are called eclipses.

 

 

Solar Eclipse

A solar eclipse occurs when the Moon comes between the Sun and the Earth. The Moon blocks the light rays from the Sun falling on the Earth and casts its shadow on the Earth. Since the Sun gets hidden by the Moon, this is called a solar eclipse. When the Moon hides the Sun completely.

it is called a total solar eclipse. When some part of the Sun is visible from the Earth, it is called a partial solar eclipse.

Sun

Moon

total eclipse

partial eclipse

Solar eclipse

Do You Know?

A solar eclipse can happen only on a new moon day and a lunar eclipse can occur only on a full moon day.

earth's orbit

penumbra

umbra

→

Earth

Moon's orbit

The centre of the shadow is the darkest region. It is called the umbra. The region of partial darkness at the edges of the shadow is called penumbra.

Never look at a solar eclipse directly; it could damage your eyes. Look at its reflection in the water or use specially designed glasses to view the solar eclipse.

Lunar Eclipse

(A lunar eclipse occurs when the Earth comes between the Sun and the Moon The Earth blocks the light rays from the Sun falling on the Moon and casts its shadow on the Moon, Since the Moon gets hidden by the Earth, it is called a lunar eclipse. When the Earth hides the Moon completely, it is called a total lunar eclipse. When some part of the Moon is visible from the Earth, it is called a partial lunar eclipse.

KEY TERMS

Solar eclipse

The shadow of the Moon formed on the Earth when the Moon comes between the Earth and the Sun

Umbra

Dark inner region of a shadow

Penumbra

Region of partial darkness at the edges of a shadow

Lunar eclipse

The shadow of the Earth formed on the Moon when the Earth comes between the Sun and the Moon

 

Solar eclipse

The shadow of the Moon formed on the Earth when the Moon comes between the Earth and the Sun

Umbra

Dark inner region of a shadow

Penumbra

Region of partial darkness at the edges of a shadow

Lunar eclipse

The shadow of the Earth formed on the Moon when the Earth comes between the Sun and the Moon

RECALL

Light is a form of energy which helps us see things around us.

Light travels in a straight line.

• Objects are of three types: transparent, translucent and opaque.

Shadows are formed when translucent or opaque objects block the path of light.

• The rotation of the Earth on its axis causes day and night.

EXERCISE

A. Tick (✔) the correct answer.

1. Which of the following is a non-luminous object?

b. Moon

2. Which of the following is a transparent object?

a. Clean water

3. Which of the following objects will not form a shadow?

c.Clear glass

4. Which of the following is true for a lunar eclipse?

b. The Earth is between the Sun and the Moon.

B. Fill in the blanks.

1.      Light travels in a straight line.

2.      A shadow is formed when light is blocked by an opaque object.

3.      Light rays can pass through transparent and translucent objects.

4.      The darkest region of a shadow is called the umbra.

 

C. Match the following.

 

Column A	Column B
1. Opaque object	d. Light cannot pass through it
2. Translucent object	e. Some light can pass through it
3. Lunar eclipse	b. Earth comes between the Sun and the Moon
4. Light	c. Form of energy that helps us see things
5. Solar eclipse	a. Moon comes between the Sun and the Earth

 

D. Give reasons for the following.

1.      Transparent objects do not form shadows because they allow light to pass through them completely. Since light can pass through, there is no blockage of light, and hence, no shadow is formed.

 

2.      We should not watch a solar eclipse with naked eyes because it can damage our eyes. The intense sunlight, especially during a solar eclipse, can burn the retina of the eye, leading to permanent damage or even blindness.

 

E. Answer the following questions in one word.

1.      Penumbra is the region of partial darkness of a shadow.

2.      The shadow cast by heavenly bodies on each other is called an eclipse.

 

F. Answer the following questions in brief.

1. What are the conditions needed for the formation of a shadow?

Conditions needed for the formation of a shadow:

• Source of light: A shadow is formed only when light falls on an opaque object.  
• Opaque object: An opaque object is needed to block the light and cast a shadow.  
• Screen or surface: A screen or surface is needed for the shadow to be projected on.  

2. Why should we make shadow puppets with opaque objects?

Why we should make shadow puppets with opaque objects:

• Clearer shadows: Opaque objects block light completely, resulting in clear and well-defined shadows.

3. What are the characteristics of a shadow?

·  Characteristics of a shadow:

• Formation: A shadow is always formed on the opposite side of the source of light.  
• Colour: A shadow is mostly black or gray, but its color can vary depending on the object and the color of the source of light.
• Shape: A shadow only shows the outline of the object and not the details.  
• Size: The size of the shadow depends on two factors:
• The distance between the object and the source of light.  
• The distance between the screen and the object.

 

G. Answer the following questions in detail.

1. Explain lunar eclipse with the help of a labelled diagram.

1. Lunar Eclipse:

A lunar eclipse occurs when the Earth comes between the Sun and the Moon, casting its shadow on the Moon.

 

2.       Differentiate between transparent, translucent and opaque objects.

Differentiating between Transparent, Translucent, and Opaque Objects:

• Transparent Objects: These objects allow most of the light to pass through them, forming a clear image on the other side. Examples: clear glass, water, air.
• Translucent Objects: These objects allow some light to pass through them, but the image formed is blurry. Examples: frosted glass, tracing paper, oiled paper.
• Opaque Objects: These objects do not allow any light to pass through them. Examples: wood, metal, thick paper.

 

Critical Thinking

1. Why does the Sun never come between the Earth and the Moon?

The Sun is significantly larger and farther away from the Earth and Moon compared to the Moon's distance from the Earth. Due to this vast difference in size and distance, the Sun's orbit does not bring it between the Earth and the Moon.  

2. Do birds flying high in the sky cast their shadow on the Earth? If yes, why is the shadow not visible?

Yes, birds flying high in the sky do cast shadows on the Earth. However, these shadows are often not visible to us for the following reasons:

• Small size of the shadow: The higher the bird flies, the smaller and less distinct its shadow becomes.  
• Diffuse nature of sunlight: Sunlight is diffused as it reaches the Earth's surface. This diffusion can further reduce the visibility of the bird's shadow.  
• Background interference: The shadow of a bird might be obscured by other objects, such as trees, buildings, or other birds, making it difficult to observe.