CLASS-IX

FORCES AND LAWS OF MOTION

WORKSHEET-L1

Sub-topics:: a) Balanced and Unbalanced force

                         b) Inertia

        A. Pick the correct option:

1. An unbalanced force acts on a body. The body

a)      must remain at rest

b)      must move with uniform velocity

c)      must be accelerated

d)      must move along a circle

2. If a body is not accelerated,

a)      no force acts on it

b)      no unbalanced force acts on it

c)      the resultant force is not zero

d)      a single force acts on it

    

3. If no force acts on a body, it will

a)      get deshaped

b)      move with increasing speed

c)      either remain at rest or move in a straight line

d)      break

4. Which of the following has the largest inertia?

a)      A pin

b)      An inkpot

c)      Your physics book

d)      Your body

5. The inertia of an object tends to cause the object

a)      to increase its speed

b)      to decrease its speed

c)      to resist any change in its state of rest or motion

d)      to decelerate due to friction

      

        B. Short –Answer Questions

                Q1. In a tug of war the rope does not move in any direction. Why?

                Q2. Can balanced forces change the shape and size of a body?

               Q3. It is easier to push an empty box than to push the box full of
                      books.Why?

               Q4. Two balls of the same size but of different materials, rubber
                      and iron are kept on the smooth floor of a moving train. The
                      brakes are applied suddenly to stop the train. Will the balls
                      start rolling? If so, in which direction? Will they move with
                      the same speed?Give reasons for your answer.

              Q5. A body at rest opposes the forces which try to move it.

                     What is this property called?

              Q6. If a ball is moving on a frictionless horizontal surface and no
                     forces are applied on it, will its speed increase, decrease or
                     remain constant?

Atmospheric refraction and scattering

    

CLASS-X

HUMAN EYE AND COLOURFUL WORLD

ASSIGNMENT-2

Q1. Why do we see seven colours due to refraction by a glass prism but, not due to refraction by a glass slab?

Q2. What are the factors affecting refractive index of air?

Q3. Why do we observe the apparent random wavering or flickering of objects when seen through a turbulent stream of hot air rising above fire?

Q4. List the three phenomenon of light responsible for formation of rainbow in the sky.

Q5. Can an observer see a rainbow on the moon? Why? Why not?

Q6. List 3 situations where u can observe tyndall effect.

Q7. On a sunny day, stand at a certain distance from a fountain of water such that the position of the sun is at your back. What do you observe? Explain the reason for your observation.

Q8. Is the position of a star as seen by us its true position? Justify your answer.

Q9. Does a beam of white light give a spectrum on passing through a hollow prism?

Q10. What would have happen if there would have been no atmosphere on the Earth?

Q11. Name any 3 phenomenon based on scattering of light.

Q12. Why are the clouds generally white?

Eye

CLASS-X

THE HUMAN EYE AND THE COLOURFUL WORLD

ASSIGNMENT-1

Q1. Name the outermost part of human eye.

Q2. Write the function of iris in the human eye.

Q3. Name the type of lens used to correct presbyopia.

Q4. 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?

Q5. Why do we have two eyes instead of one eye?

Q6. A student 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?

Q7. What happens to the image distance in the eye when we increase the distance of an object from the eye?

Q8. A chicken can see only in the bright light. What type of cells are present in its retina?

Q9. A person is unable to see objects nearer than 50cm. He wants to read a book placed at a distance of 25cm. Find the nature, focal length and power of the lens, he requires for his spectacles.

Ans : f= +50cm , P=2D, convex lens

Q10. The near point of a hypermetropic eye is 1m. What is the power of the lens required to correct this defect? Assume that the near point of the normal eye is 25cm.

Ans:  f= 33.3cm=0.33m

         P=+3.0D (convex lens )

Q11. A person is able to see objects clearly only when these are lying at distance between 50cm and 300cm from his eye.

i)                   What kind of defect of vision he is suffering from?

ii)                 What kind of lens will he require to increase his range of vision?

Q12. A person can see clearly only up to 3m. Prescribe a lens for spectacles so that he can see clearly up to 12m. Defect is myopia.

Ans : A concave lens of focal length 4m should be used.

Stars and Solar System

CLASS-VIII

STARS AND SOLAR SYSTEM

ASSIGNMENT-8

Q1. Fill in the blanks:

a)    A celestial body that revolves around a planet is known as ______________ while that revolving around a star is called a _______________.

b)    Asteroids are found between the orbits of ____________ and _____________.

c)     Alpha centauri is at a distance of ______ light years from the earth.

d)    One A.U. = _____________m.

e)     The temperature on the moon varies from ________ at noon to _______ at night.

f)      A day on mercury equals nearly _____ earth days.

g)    One ‘Jupiter Year’ equals nearly ______ earth years.

h)    The tail of a comet is always directed ________ from the sun.

Q2. Name any 3 artificial Indian satellites.

Q3. Give the other name of meteors.

Q4. Name the astronauts who landed on moon in 1969.

Q5. Name the two bright stars present in Orion constellation.

Q6. List 3 conditions which help in sustaining life on Earth.

Q7. Draw a labelled diagram to show the position of the earth in different seasons.

Q8. What do you understand by the statement that a star is 8 light years away from the Earth?

Q9. Draw sketches to show the relative positions of prominent stars in

a)    Ursa Major

b)    Orion

Q10. Name the inner planets and the outer planets of the solar system.

Synthetic fibres and plastics

CLASS-VIII

SYNTHETIC FIBRES AND PLASTICS

ASSIGNMENT-7

Q1. Fill in the blanks:

a)     Synthetic fibres are also called _______________ or ______________ fibres.

b)    Terycot is a mixture of _________________ and _______________.

c)     ___________ is used for making bottles of soft drinks, oils etc.

d)    ______________ was the first man-made plastic.

e)     Thermosetting plastics have a __________________ arrangement of molecules.

f)      Teflon is a ________________ plastic.

g)     _______________ is a flame resistant plastic.

Q2. Match the following:

1.     Terylene                          a) Prepared by using wood

                                                  pulp

2.     Teflon                              b) Used for making

                                                  parachutes and stockings

3.     PET                                 c)  Fabrics do not wrinkle

                                                   easily

4.     Rayon                              d) Used to make non-stick

                                                  cookwares

5.     Nylon                              e)  Used for making magnetic

                                                   tapes

Q3. Synthetic fibres are not considered environment friendly. Why?

Q4. What do you understand by high tensile strength?

Q5. Define polymerization.

Q6. Why synthetic fibres are used for making dress materials?

Q7. a) What is the other name of artificial silk?

       b) How is it prepared?

       c) Why is it also called regenerated fibre?

Q8. Explain the difference between:

a)     thermoplastic and thermosetting plastic

b)    biodegradable and non-biodegradable materials

Q9. Write 3 uses of melamine.

Q10. Why is Teflon used to make non-stick cookwares?

Q11. Explain why the following are made of thermosetting plastics:

a)     Saucepan handles

b)    Electric plugs/ switches/ plug boards

Q12. Why is melamine coated on uniform of fireman?

Q13. Why electrical wires have plastic covering?  OR 

         Why handles of screw drivers are made of plastic?

Q14. Explain why plastic containers are favoured for storing food?

Q15. Write any 2 measures that can be taken to control the damage caused by plastic waste.

Sound

CLASS-VIII

SOUND

ASSIGNMENT-6

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.

 

Numericals based on concave/convex lens and power

CLASS-X

LIGHT

ASSIGNMENT-3­

Q1. A 4cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 20cm. If the distance of the object is 30cm from the lens, find the position, nature and size of the image. Also find its magnification.                                                  

Ans: v=60cm, h_i= -8cm, inverted, m= -2

Q2. A needle placed at 45cm from the lens forms an image on a screen placed 90cm on the other side of the lens. Identify the type of the lens and determine its focal length.

Ans: f= +30cm, convex lens

Q3. An object 2cm high is placed at a distance of 64cm from a white screen. On placing a convex lens at a distance of 32cm from the object it is found that a distinct image of the object is formed on the screen. What is the focal length of the convex lens and size of the formed on the screen?

Ans: f= 16cm, h_i= -2cm (same size, inverted)

Q4. A 10cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 30cm. The distance of the object from the lens is 20cm. Find the position, nature and size of the image formed.

Ans: v= -60cm, h_i= +30cm, erect

Q5. One-half of a convex lens is covered with a black paper. Will this lens produce a complete image of the object? Verify your answer experimentally. Explain your observations.

Q6. A concave lens of focal length 20cm forms an image at a distance of 10cm from the lens. What is the distance of the object from the lens?

Ans: u= -20cm

Q7. Find the position and nature of image formed when an object is placed at a distance of 5cm from a concave lens of focal length 15cm. What is its magnification?

Ans: v= -3.75cm, virtual and erect, m= 0.75

Q8. An object located 32cm in front of a lens forms an image on a screen 8cm behind the lens.

a)     Find the focal length of the lens.

b)    Determine its magnification.

c)     Is the lens converging or diverging?

Ans: f= 6.4cm, m= -1/4, convex lens

Q9. An object 60cm from a lens gives a virtual image at a distance of 20cm in front of the lens. What is the focal length of the lens? Is the lens converging or diverging?

Ans: f= -30cm, lens is diverging or concave

Q10. Find the power of a concave lens of focal length 2m.

Ans: P= -0.5D

Q11. A doctor has prescribed a corrective lens of power +1.5D. Find the focal length of the lens. Is the prescribed lens converging or diverging?

Ans: f= +0.67m, converging

Q12. A concave lens of power -2D is placed in contact with a convex lens of power +1.5D. What will be the resultant power?

Ans: P= -0.5D

Q13. A lens has a power of -0.25D. Identify the type of lens and what will be the focal length?

Ans: Concave, f= -4m

Q14. 3lenses of powers 2D, -0.25D, 1.75D are placed in contact. Calculate the net power of the arrangement. Will it produce a converging or a diverging effect? Will the net power change if the order of lens placement is changed?

Ans: P= +3.5D, converging effect, No

Q15. A convex lens forms a real and inverted image of a needle at a distance of 50cm from it. Where is the needle placed in front of the convex lens if the image is equal to the size of the object? Also find the power of the lens.

Ans: 50cm, P= 4D