### Some Natural Phenomena - Exemplar Solutions 3

CBSE Class 8 Science
NCERT Exemplar Solutions
CHAPTER – 15
SOME NATURAL PHENOMENA

16. During the construction of a building the lightning conductor was left hanging in the air by mistake. Would the lightning conductor be still effective ? Explain.
Ans: No, lightning conductor will not be effective. Since lightning conductor was not connected properly to the earth, therefore, the charge will not pass through to the earth.

17. If air and cloud were good conductors of electricity, do you think lightning could occur ? Explain.
Ans: Air current move in the upward direction while the water droplets move in downward direction. These movements cause separation of charges in such a way that the positive charges collect near the upper limits of the clouds whereas the negative charges accumulate near the lower limits. There is accumulation of positive charges near the ground also. When the magnitude of the accumulated charges becomes very large, the air being a poor conductor of electricity, is no longer able to repel their flow. Negative and positive charges meet giving rise to lighting.
But if air and clouds became good conductor of electricity this phenomenon will not take place because positive and negative charge will meet at very small accumulated charge.

18. Identify the lightning conductor and the copper plate in Fig. 15.2.
Ans: A is the lightning conductor and B is the copper plate.

19. If the materials used for constructing a building were good conductors, do you think lightning will strike the building. Will the lightning conductor be still required to be installed in the building ?
Ans: No, there is no need to install lightning conductor in the building if the materials used for constructing a building were good conductors.
Explanation: Since, building will pass the electricity due to lighting to earth directly.

20. You might have observed on a dry day that when you touch the screen of a television or computer monitor (with picture tube), you get a slight shock. Why does it happen ?
Ans: Electric charge gets accumulated on the screen. On touching the screen of a television or computer monitor (with picture tube), the charge discharges through our body. Thus, we get a slight shock.

21. Explain how does lightning conductor protects a building from getting struck by lightning.
Ans: Lightning conductor does not allow the charge to accumulate on a building as it conducts the charge to the earth, protecting building from being struck by lightning.

22. In an electroscope if a negatively charged body is brought in contact with the metal clip, the strips of the electroscope diverge. If now another charged object carrying equal amount of positive charge is brought in contact with the clip, what will happen ?
Ans: If a positively charged object is brought in contact with the clip of an electroscope, the negative charge given earlier will be neutralised and the strips will collapse.

23. The strips of an electroscope diverge when a charged body is brought in contact with the metal clip. Now the clip is touched gently by our hand. What will happen to the strips ? Explain.
Ans: The charge that was in the electroscope strips will get discharged through our body to the earth after the clip is touched gently by our hand. The strips will come back to the original state.