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21 July 2014

CLASS VIII physics Chapter Sound Solve CBSE Exam Assignments

Q.1 How does a sound making object differ from one that is silent?
Answer: Sound making object can vibrate easily.                      
Q.2 How does sound from a sound producing body travel through air to reach our ears?
Answer: Sound from a sound producing body travel through air to reach our ears by making regular compression and rarefaction.
Q.3  Why are the voices of men, Women and children different?
Answer: The voices of men, women and children differ from each other due to the following factors:
1) The pitch is one of the most essential factors to determine the voice of the individual. For example, men have lower-pitched voices while women have higher-pitched voices.
2) Second factor which brings in the difference in the voices is the length and the thickness of vocal cords.
Q.4  Why a sound cannot be heard on the moon?
Answer: A sound cannot be heard on the moon due to absence of medium air
Q.5  How do astronauts talk to one another on the surface of moon and Why?
Answer:  Astronauts communicate with the help of radio waves on moon because these waves do not need a medium to travel
Q.6  If you want to hear a train approaching from far away, why is it more convenient to put the ear to the track?
Answer: This is because sound can travel through railway track (solid ) faster than through air.
Q.7  State one observation from everyday life which shows that sound travels much more slowly than light?
Answer: We hear thunder after lightining.
Q.8  What is the scientific name for the following? The number of vibrations made per second.
Answer: Frequency
Q.9   Why do we not hear the screams of a bat?
Ans: This is because the screams are ultra sonic(above 20,000 hertz) which human ear cannot hear.
Q.10  Which of the following frequency of sound can be heard by a dog but not by a man?                                                                     (a) 50,000 hertz (b)   15,000 hertz
Answer:  A sound of frequency 50,000 hertz can be heard by a dog but not by a man
Q.11 Explain how, noise pollution {or excessive loud noise} is harmful to human beings.
Answer: Noise pollution can lead to a number of health-related problems. Some of them are as follows:
(i) Hearing loss  (ii) inability to sleep         (iii) Hypertension (iv) Severe headache (v) Stress
Q.12  State the various measures which can be taken to control {or reduce} noise pollution in our surroundings.
Answer: Noise pollution can be reduced by using silencers in vehicles, industrial machines, and home appliances reducing use of vehicle horns, running TV, radio and music systems at low volumes. Planting of trees along roads and buildings also help to reduce noise pollution.
Q.13 Give two causes of noise pollution from the homes.
Answer: . In the home noise pollution is caused by television radio and  music systems at high volume, some kitchen appliances, desert coolers, air conditioners etc.
Q.14   Sound of different pitch can be produced using a flute. Explain, how?  
Answer: If we blow a flute, the air column vibrates and produces sound. Flute contains small air columns, when air is bowed through the mouth piece the air columns start vibrating which produces sound.
Q.15.How does Sound produced by humans?
Answer:     In humans sound is produced by the vioce box or larynx. It is the upper part of the wind pipe. Two vocal cords are stretched across the voice box leaving a narrow slit. When the lungs force air through the slit, it vibrates and produces sound.
Q. 16. How Jal Tarang produces sound?
Answer: In Jal-tarang musical instrument the cup containing minimum water produces the sound of lowest frequency or lowest pitch. As the amount of water in the cup goes on increasing, the frequency (or the pitch) of the sound produced also goes on increasing.
Q. 17. If 125 oscillations are produced in 5 seconds, what is the frequency in hertz?
Answer: in 5 seconds 125 oscillations are produced
So, in 51 seconds 125/5 = 25 oscillations are produced
Hence, the frequency = 25Hz
Q. 18. What is the frequency of a vibrating body whose time-period is 0.05 second?              
Answer: f = 1/t = 1/0.05 = 100/5 = 20HZ
Q. 18. State true or false
(i) Sound can be produced by beating an object irrespective of whether there are vibrations or not.
(ii)The sound of a tabla normally has a lower pitch than the sound of a violin.
(ii)A short flute will produce sound of lower pitch than a long flute.
Answer: (i) –False [Sound is produced from a vibrating object.]
(ii) -True [The sound of a tabla normally has a lower pitch than the sound of a violin.]
(iii) –True[A short flute will produce sound of lower pitch than a long flute.]
Q.19. Give reasons Why Trees planted along the roads reduce noise?
Answer: Trees are planted along the roads and around buildings so that it could cut off sound vibrations produced from vehicles speakers etc. by absorbing them, hence leading in prevention of Noise pollution.
Q.20. what are transverse and longitudinal waves?
Answer: Longitudinal waves: A wave in which the particles of the medium vibrate back and forth in the same direction in which the wave is moving is called longitudinal wave. Example: sound waves.
Transverse waves: A wave in which the particles of the medium vibrate at right angles to the direction, in which the wave is moving, is called transverse wave. Example: Light waves.
Assignments for practice 

1. How sound is produced?

2. What do you understand by a ‘wave’?

3. Write three differences between sound and light waves.

4. What do you understand by “sound energy cannot be produced”?

5. What is the name of the wave that can travel through vacuum?

6. Explain by some experiment that sound waves require medium for their propagation.

7. How sound waves travel through some medium?

8. Why sound waves do not propagate through vacuum?

9. What are the transverse waves? Give two examples.

10. What are longitudinal waves? Give two examples.

11. Give two points of difference between longitudinal and transverse waves.

12. How will you prove that the sound waves exhibit longitudinal behaviour?

13. What are rarefaction and compression in case of sound waves?

14. Distinguish between crests and troughs.

15. Write the SI unit of velocity of a wave.

16. What are the factors that describe the sound wave and define them?

17 Why is a thundering sound heard later than lightening?

18. Sound travels with different speeds in different media. Comment.

19. How far is a compression and its nearest rarefaction in a longitudinal wave?

20. Define sound ranging.

21. What is the frequency range of sound for human beings?

22. What are the ultrasonic and supersonic waves?

23. What type of waves are produced by animals like bats and dolphins?

24. Explain two applications of ultra sound waves?

25. Explain how ultrasound waves are used to detect a flaw in an object?

26. Which sound wave is used in ECG (echocardiography)?

27. Give the full form of SONAR.

28. Name the technique used to measure the depth of a sea.

29. How will you determine the depth of a sea using SONAR?

30. How do the bats fly in dark?

31. How RADAR is different from SONAR?

32. Explain the function of ear by explaining its each part.

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03 July 2014

X Science Questions From CBSE Examination Papers Ch: Magnetic Effect of currents

1. Q. What is solenoid? Draw the pattern 0f magnetic field line of a solenoid through which steady current flows
2 Marks
2. Q. What are permanent magnet and electromagnet? Give two use of each.
2 Marks
3. Q. Differentiate short circuit and over loading?
2 Marks
4. Q. Draw the pattern of magnetic field lines of produce by current carrying circular loop
2 Marks
5. Q. What is role of fuse in domestic circuit? Why we use the fuse of defined rating not be replaced by one with large rating?
2 Marks
6. Q. How will deflection of compass get affected if current in straight wire is increased? support your answer with reason?                                        
2 Marks
7. Q. No two field line intersect each other . Explain?                          
2 Marks
8. Q. What is the direction of thumb indicates in right hand thumb rule? In what way this rule is different from Fleming’s left hand rule?  
2 Marks
9. Q. Why does a current carrying conductor kept in a magnetic field experience force? On what factor does the direction of this force depend? Name and state the rule used determination of direction of current?
2 Marks
10. Q. Two circular coil A and B placed closed to each other If the current in coil A is changed, will some current be induced in the coil B? Give reason?
2 Marks
11. Q. What do you mean by term magnetic field line? List any two properties?
2 Marks
12. Q. Give an activity to show magnetic field produce by current carrying circular loop?
2 Marks
13. Q. What precautions should be taken to avoid the overloading of domestic circuit? 
2 Marks
14. Q. Why do we connect earth wire in house give two reason?
2 Marks
15.Q. Write four properties of magnetic field lines?
2 Marks

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X CBSE Physics Guess Paper Solved Ch.Magnetic effects of currents

1. A magnetic compass shows a deflection when placed near a current carrying wire. How will the deflection of the compass get affected if the current in the wire is increased? Support your answer with a reason.
Answer:   The deflection increases. The strength of magnetic field is directly proportional to the magnitude of current passing through the straight conductor.
2.  Meena draws magnetic field lines of field close to the axis of a current carrying circular loop. As she moves away from the centre of the circular loop she observes that the lines keep on diverging. How will you explain her observation
Answer:  Strength of the magnetic field falls as distance increases. This is I indicated by the decrease in degree of closeness of the lines of field.
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X- Guess Questions solved SA-1: Magnetic effects of currents