SOUND

CLASS-VIII

SOUND

Q1. Fill in the blanks:

a)     Time taken by an object to complete one oscillation is called______________.

b)    Loudness is determined by the____________________ of vibration.

c)     The unit of frequency is____________.

d)    Unwanted sound is called_____________.

e)     Shrillness of a sound is determined by the_______________ of vibration.

f)      The three tiny bones present in the ear are_____________,____________ and______________.

g)     The effect of sound stays on the ear drum for about_________.

h)     __________is the minimum distance to hear an echo.

i)       Noise is produced by_______________ vibrations.

j)       For human ears the audible range is ___________ to ____________.

Q2. In which medium sound travels fastest: air, water or steel?

Q3. Name the type of waves which are used by astronauts to communicate with another on moon (or in outer space).

Q4. Which property of sound leads to the formation of echoes?

Q5. Choose the infrasonic waves and ultrasonic waves from the following frequencies:

a)     30,000 Hz

b)    18 Hz

c)     50,000 Hz

d)    10 Hz

Q6. Which of the following sound frequencies cannot be heard by a human ear?

a)     10 Hz

b)    100 Hz

c)     10,000 Hz

d)    15 Hz

e)     40,000 Hz

Q7. What type of sound waves is produced by a vibrating simple pendulum?

Q8. What is the name of the device which is used to find the depth of sea (or ocean) by using ultrasonic sound waves?

Q9. Name two animals which can produce ultrasonic waves.

Q10. Name the three characteristics of sound.

Q11. Name the characteristic which helps us distinguish between a man’s voice and a woman’s voice, even without seeing them.

Q12. A cricket ball is seen to hit the bat first and the sound of hitting is heard a little later. Why?

Q13. When we put our ear to a railway line, we can hear the sound of an approaching train even when the train is far off but its sound cannot be heard through the air. Why?

Q14. On which day, a hot day or a cold day, an echo is heard sooner? Give reason for your answer.

Q15. Why should we not put a pin or a pencil in our ears?

Q16. What is the function of 3 tiny bones in the middle ear?

Q17. A pendulum oscillates 40 times in 4 seconds. Find its time period and frequency.

Q18. The sound from a mosquito is produced when it vibrates its wings at an average rate of 500 vibrations per second. What is the time period of the vibration?

Q19. A man standing 825 metres away from a cliff fires a gun. After how long will he hear its echo? Speed of sound in air is 330m/s.

Q20. The echo of a sound is heard after 3seconds. If the speed of sound in air be 330m/s, calculate the distance of the reflecting surface.

Q21. What is meant by the quality of sound?

Q22. The quality of sound produced by men, women and children is different. Why?

Q23. Explain why, if we strike a tabla lightly , we hear a soft sound but if we hit the tabla hard, a lound sound is heard.

Q24. What is the difference between noise and music? Can music become noise sometimes?

Q25. List sources of noise pollution in your surroundings.

CLASS-VIII

COMBUSTION

Q1. Fill in the blanks:

            a )    Fuel must be heated to its______________________ before it starts burning.

            b)     Fire produced by oil cannot be controlled by ________________.

            c)      ______________ is essential for combustion.

            d)     Fuel efficiency is expressed in units ___________.

            e)      ________________ fuels have highest calorific value.

            f)      Incomplete combustion of carbon produces __________________________ gas.

            g)     Complete combustion of carbon produces ___________________________ gas.

            h)      ___________________________ is the coldest part of the flame.

            i)       Luminous zone is _______________ in colour.

            j)       _________ phosphorous is present in matchstick.

Q2. What are inflammable substances? Give example.

Q3. Name 4 types of combustion. Give one example of each.

Q4. Differentiate between rapid and spontaneous combustion.

Q5. Name the unit in which the calorific value of a fuel is expressed.

Q6. Explain how CO₂  is able to control fires.

Q7. Which substances on burning give a flame?

Q8. Camphor burns with a flame, but charcoal glows. Why?

Q9. Which zone of a flame does a goldsmith use for melting gold and silver and why?

Q10. What is the basic principle in controlling fire?

Q11. Give reasons:

                i)   Paper by itself catches fire easily whereas a piece of paper wrapped around an aluminium pipe does not.

               ii)   It is difficult to burn a heap of green leaves but dry leaves catch fire easily.

Q12. 1kg of LPG produces 55000 kJ of energy. What is the calorific value of LPG?

Q13. In an experiment 4.5kg of a fuel was completely burnt. The heat produced was measured to be 1,80,000 kJ. Calculate the calorific value of the fuel.

Q14. Abida and Ramesh were doing an experiment in which water was to be heated in a beaker. Abida kept the beaker near the wick in the yellow part of the candle flame. Ramesh kept the beaker in the outermost part of the flame. Whose water will get heated in a shorter time?

HUMAN EYE

CLASS-VIII

THE HUMAN EYE

Q1. Name the outermost part of human eye.

Q2. Name the part of human eye which acts as a screen to obtain the image of an object.

Q3. Name two common defects of vision.

Q4. A child wears spectacles fitted with concave lenses. Name the defect of vision.

Q5. When we enter a dim-lit room from a bright light, we are not able to see the object in the room for some time. Explain, why?

Q6. Why do we have two eyes instead of one eye?

Q7. A child has difficulty in reading the black board while sitting in the last row. What could be the defect the child is suffering from? How can it be corrected?

Q8. What is the function of iris in the eye?

Q9. a) Which muscle controls the focal length of the eye lens?

       b) Which nerve sends the image to the brain?

Q10. Which phenomena is used in cinematography?

Q11. What happens to the image distance in the eye when we increase the distance of an object from the eye?

Q12. What type of lens is an eye lens?

Q13. Why does a person suffering from hypermetropia prefers to remove his spectacles while looking at distant objects? Explain.

Q14. Why do chickens wake up early and sleep early?

Q15. Visit an eye surgeon of your locality. Find out the following facts:

a)     Which part of our eye is donated at the time of eye donation?

b)    For how long the donated eye can be preserved?

c)     Who can’t donate his eyes?

Reappearing coin in a bowl

Synchronous rotation of the moon

CLASS-VIII

WORKSHEET-S1

STARS AND SOLAR SYSTEM

Q1. The star nearest to the earth is

a)      Pole star

b)      Sun

c)       Alpha centauri

d)      Proxima centauri

Q2. All the constituents of the milky way galaxy move

a)      Along a straight line away from its centre

b)      Around its centre

c)       Along a straight line towards its centre

d)      Along an ever changing zig-zag path

Q3. Stars having a very high temperature appear

a)      Red

b)      Blue

c)       White

d)      Yellow

Q4. Which two gases are present in the atmosphere of the largest planet? Of what is its cloud cover made of?

Q5. What are the satellites that generally appear to remain fix w.r.t the earth called? Write its one application also?

Q6. Rita observes an object in the sky which seems brightest after the sun and the moon. It is known that its size is nearly the same as that of the earth and it shows phases like moon.

a)      Identify the planet.

b)      What is its sense of rotation relative to that of earth?

Q7. List 3 conditions which help in sustaining life on earth.

Q8. Draw a labelled  diagram to show the position of the earth in different seasons.

Q9. What do you understand by the statement that a star is 4.3 light years away from the earth?

Q10. Draw the sketches to show the relative positions of prominent stars in:

a)      Ursa major

b)      Orion

c)       Cassiopeia

Q11. Why is mercury or venus often called morning or evening star?

Q 12. Fill in the blanks:

a)      Comet means a ___________ star.

b)      The colour of a star is determined by its ____________________.

c)       The big dipper constellation is also known as ___________________.

d)      Pole star defines ______________ direction.

e)      The temperature on the moon ranges from _____ _to ________.

f)       Asteroids are found between the orbits of _________ and __________.

g)      Moon takes nearly ______ days to make one complete revolution around the earth.

h)      Alpha centauri is at a distance of ________________ from the earth.

i)        Halley’s comet appears after every________ years.

j)        The tail of a comet is always directed _________ from the sun.

Q13.  Name the following:

a)      Red planet                                       

b)      Two Indian satellites                  

c)       Morning or evening star              

d)      Earth’s  galaxy        

e)      Largest asteroid

f)       Largest planet

g)      Brightest star in the night sky

h)      Two natural satellites of mars

i)        Artificial satellite

j)        Third largest planet

k)      Second nearest star to the earth

l)        Planet named after roman sea god

Q 14. Name the planet whose northern hemisphere remains in darkness for 40years. Which two gases have been detected in the atmosphere of this planet?

Q15.  What are comets? Name any one periodic comet.

Q16.   Differentiate between:

a)      Terrestrial and jovian planets

b)      Artificial and natural satellite

CLASS-VIII

SOURCES OF ENERGY

WORKSHEET-SE1

A. MCQs:

1. Natural Gas is an example of

a)      Renewable and exhaustible source of energy

b)      Non-renewable and exhaustible source of energy

c)      Renewable and inexhaustible source of energy

d)      Non-renewable and inexhaustible source of energy

2. Coal and Petroleum are

a)      natural resources             c)     fossil fuels

b)      exhaustible resources      d)    all of the above

3. Which of the following represents water gas?

a)      CO₂  +  H₂

b)      CO + O₂

c)      CO + H₂

d)      O₂  +  H₂

4. Which of the following is not a renewable source of energy?

         a)      Sun                       c)  Biomass

b)   Petroleum              d)  Wind

5. Which is not a clean fuel?

  a)    LPG                                  c)    Petrol

  b)    CNG                                 d)    Biogas

B. Fill in the blanks:

1. __________ is used for extraction of metals.
2. Petroleum gas liquefied under pressure is called________________.
3. Natural gas is found between __________ and _______________.
4. ____________ is the largest source of CO₂  emissions.
5. ________ and _________ are used as domestic fuels.

C. Short-ans questions:

1. Why is coal a better fuel than wood?
2. Name 3 places where gas fields have been discovered in India.
3. Give 2 uses of natural gas.
4. Why is asphalt coated at the underside of electric poles?
5. List four forms of energy that you use from morning when you wake up, till you reach the school.
6. Write some characteristics of a good fuel. ( at least 3)
7. What is geothermal energy?
8. Hydrogen has been used as a rocket fuel. Would you consider it a cleaner fuel than CNG? Why or why not?