Kerala Syllabus Class 7 Basic Science: Chapter 08 Wonders of Sky - Questions and Answers


Questions and Answers for Class 7 Basic Science (English Medium) ആകാശവിസ്‌മയങ്ങൾ | Text Books Solution Basic Science (English Medium) Chapter 08 Wonders of Sky - Teaching Manual | Teachers Handbook

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ഈ ബ്ലോഗ് അഡ്‌മിൻറ രേഖാമൂലമുള്ള അനുമതിയില്ലാതെ ഈ ബ്ലോഗിൽ നൽകിയിരിക്കുന്ന ചോദ്യോത്തരങ്ങൾ, ഇതേരീതിയിലോ പി.ഡി.എഫ് രൂപത്തിലോ, മറ്റേതെങ്കിലും ഡിജിറ്റലോ, പ്രിന്റഡ് ഉൾപ്പെടെയുള്ള ഏതെങ്കിലും രൂപങ്ങളിലേക്കോ മാറ്റി മറ്റൊരു വെബ്സൈറ്റിലോ, ബ്ലോഗിലോ, യുട്യൂബ്, സോഷ്യൽ മീഡിയാ ഗ്രൂപ്പുകളിലോ ഉൾപ്പെടെ ഒരിടത്തും പ്രചരിപ്പിക്കാൻ പാടില്ലാത്തതാകുന്നു.

Std 7: Basic Science Chapter 08: Wonders of Sky - Questions and Answers

♦ Observe the picture.
● In which direction will the shadow of the tree be seen in the morning?
 The shadow will spread towards the west and the shadow is longer.

● In which direction will the shadow of this tree be in the evening? 
 The shadow will spread towards the east and the shadow is longer.

● What change can you see in it at noon?
The shadow will appear just below the tree and the shadow is shorter.

♦ Will the shape of the shadow be the same at all times?  Let’s do a simple experiment.
Materials: Pen, cricket ball, piece of glass, instrument box, plate, steel glass, football.
Hold each object against the wall in different ways and light the torch onto them. Tabulate your observations.
Object The Shape of the Shadow
• Pen• The shape changes
• Football• The shape does not change
• Cricket ball• The shape does not change
• Glass• No shadow is formed
• instrument box• The shape changes
• Plate• The shape changes
• Steel glass• The shape changes
● Do all the objects cast shadows?
No, All opaque objects form shadows

● On which side of the source of light is the shadow formed?
Shadow forms in the direction opposite to that of the source of light. 

● Which were the objects that always formed shadow of the same shape?
• Football, Cricket ball
• Only spherical objects always form circular shadow.

♦ The Earth, the Moon and other celestial bodies are opaque objects. Do they form shadows?
The Earth, the Moon do not allow sunlight to pass through it. Hence shadow is formed on the other side. 

♦ What is the shape of the Earth’s shadow? 
It looks like a cone ice cream cup.

♦ What are the facts you have understood about the Earth’s shadow?
• Being an opaque object, the Earth forms its shadow.  
• The shadow of the Earth is always formed in the direction opposite to the Sun.
• The Earth’s shadow gradually diminishes and finally disappears as it moves away.

♦ Guess whether it will be day or night where the Earth’s shadow is formed. 
• Night 
• In a celestial sphere, it is day where the light falls and night where the shadow is formed.
♦ Are shadows of all celestial bodies are the same size?
The size of the shadows varies with the change in the size of the celestial bodies.

♦ Among the following, which is the probable position of the Moon in the shadow of the Earth? 
Answer: Figure - B 

♦ The figure below shows the celestial spheres the Sun and the Earth and the Moon's orbit. B, C and D are the various positions in the path through which the Moon revolves round the Earth.
● At which of these positions does the Moon enter the Earth’s shadow?      
Answer: B

● At what position does the Moon enter completely in the Earth’s shadow?
Answer: C

● At which point does the Moon come out of the Earth’s shadow?
Answer: D

♦ What is Lunar Eclipse?
• As the Moon revolves round the Earth, the Earth sometimes comes between the Sun and the Moon in a straight line. At this time the Moon will be in the shadow of the Earth. This is the lunar eclipse.

♦ What is Solar Eclipse?
When the Moon revolves round the Earth, the Moon rarely comes in between the Earth and the Sun in a straight line.  At this time the Moon's shadow falls on the Earth. People in the area where the Moon's shadow falls cannot see the Sun because the Moon covers the Sun. This is solar eclipse. A solar eclipse is visible only to those in the lunar shadow.
♦ Different solar eclipses.
● Total solar eclipse 
• Moon completely screens the bright light of the Sun
• Corona of the Sun is visible 

● Annular solar eclipse 
• The centre of the Sun is screened by the Moon 
• The outer surface of the Sun appears as a ring

● Partial solar eclipse
The moon only partially screens the Sun.
The visible part of the Sun is crescent-shaped

♦ How can we observe a solar eclipse safely?
• Observing the solar eclipse directly is harmful to the eyes. 
• The solar eclipse must be observed only by using filters and reflecting the Sun’s rays in different ways. 
• Eclipses can be observed using quality filters in telescopes and binoculars. • Decorative glitter papers and unsafe X-ray films should not be used for observing solar eclipse. 

♦ What would be the reason for the brightness of the moon?
The sunlight falling on the Moon's surface gets scattered and reaches the Earth. This is the moonlight that we see at night.

♦ Why is the spherical Moon seen in different shapes on different days? 
Experiment
Materials needed: Three smiley balls, black paint

Procedure: Paint half of each smiley ball with black paint as suggested in the notes in the boxes. 
The black painted part represents the shadow side of the Moon. The unpainted part represents that part of the Moon where light falls.

Place the balls in the class in east-west direction as shown in the picture
below. 
The unpainted part of the smiley ball should face the light and the black-painted part should face the side opposite of light. Imagine the smiley ball as the Moon and the bulb as the Sun. A, B and C are the positions when the Moon revolves around the Earth. The child should sit in the middle of balls A and C and observe.

Observation: 
On the ball placed at A the child can see the shadow portion completely.
The ball placed at B position enables the child to view half-illuminated and half-shadow portions
On the ball at position C the child can see the illuminated portion completely.

Inference: New Moon occurs when the shadow side of the Moon completely faces the Earth. We cannot see the Moon on this day. Full Moon occurs when the illuminated part of the Moon completely faces the Earth. Half Moon is seen when the half-illuminated and half shadow portions of the Moon face the Earth.

● As per the picture, how will the child be viewing all the three balls? 
On which ball can the child see the shadow portion completely? 
Answer: A

● Ball placed at which position enables the child to view half-illuminated and half shadow portions?
Answer: B

● On which ball can the child see the illuminated portion completely? 
Answer: C

♦ New Moon 
New Moon occurs when the shadow side of the Moon completely faces the Earth. We cannot see the Moon on this day. 

♦ Full Moon
Full Moon occurs when the illuminated part of the Moon completely faces the Earth.

♦ Half Moon
Half Moon is seen when the half-illuminated and half-shadow portions of the Moon face the Earth.

♦ Observe the pictures given below. The two pictures A and B represent the revolution of the Moon from New Moon to Full Moon and vice versa. 
● Which picture shows the illuminated portion of the Moon getting increased, when viewed from the Earth?  
Answer: Picture A

● Which picture shows the illuminated portion of the Moon getting decreased, when viewed from the Earth?  
Answer: Picture B

♦ What is Waxing and Waning?
• When viewed from the Earth, the illuminated part of the Moon keeps on increasing from the New Moon to Full Moon. This period is known as the waxing or white halo.
• When viewed from the Earth, the illuminated part of the Moon keeps on decreasing from the Full Moon to New Moon. This period is known as the waning or black halo.
• Waxing and waning (Vridhikshayam) is the difference in viewing the illuminated and shadow portions of the Moon as it revolves around the Earth. 

♦ Which are the symbols used in the calendar to indicate the New Moon and Full Moon day?
The symbol⚫and the symbol 〇 are used in a calendar to represent New Moon and Full Moon respectively.

♦ Observe the given calendar and find out how many days it takes for the Moon to reach the New Moon from Full Moon.
♦ Examine the next month’s calendar also. Find out how many days are needed for the Moon to reach the next New Moon from the Full Moon? 
♦ The Moon takes 27 ⅓ days to revolve around the Earth once. It takes 30 days for one New Moon to reach the next. What is the reason for this difference?
The Earth needs 365 ¼ days to revolve around the Sun once. By the time the Moon revolves around the Earth once, the Earth would have travelled some distance in its orbit with the Moon around the Sun. Thus a change occurs to the position of the Earth. Hence the Moon will have to travel some more distance in the same path to repeatedly see the phases of the Moon. It takes more than two days for this. That is why it takes 29 ½ days from one New Moon to the next New Moon.

Let’s Assess

1. Observe the picture. Check the orbital path of the Moon around the Earth and complete the table below:
2. Observe the picture and complete the table by matching the boxes appropriately.
3. Some statements are given below. Tick (✔) the correct ones.
• A Full Moon is the day when the part of the Moon on which the sunlight falls, is completely visible from the Earth. (✔)
• The waxing crescent Moon is visible overhead at sunset. (✔)
• The period of revolution of the Moon and the period during waxing will be visible are the same. (X)
• Solar eclipse occurs only on New Moon day. (✔)
• Lunar eclipse occurs only on Full Moon day. (✔)
• Lunar eclipse occurs on all Full Moon days. (X)




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