Chapter 8 – Static Electricity
1. Choose the correct option and fill in the blanks.
(always repulsion, always attraction, displacement of negative charge, displacement of positive charge, atom, molecule, steel, copper, plastic, inflated balloon, charged object, gold)
(a) There is ________ between like charges.
Ans: always repulsion
(b) ________ is responsible for generation of electric charge in an object.
Ans: Displacement of negative charge
(c) A lightning conductor is made of a ________ strip.
Ans: copper
(d) ________ does not get electrically charged easily by rubbing.
Ans: Plastic
(e) There is ________ when opposite electric charges come near each other.
Ans: always attraction
(f) A ________ can be detected with an electroscope.
Ans: charged object
2. Explain why it is not safe to go out with an umbrella when there is heavy rain, lightning or thunder.
Ans: Generally, the central rod of an umbrella is metallic, with a pointed tip at the upper extremity. Moreover, the ribs of an umbrella are also made of metal. When there is heavy rain along with lightning and thunder, the lightning strike can be attracted towards the umbrella. This attraction is between the opposite charges on the cloud and the umbrella. Since our body is a good conductor of electricity, we may get a forceful shock. This can be lethal, too. In order to avoid such a hazard, it is not safe to go out with an umbrella when there is heavy rain.
3. Answer in your own words.
(a) How will you protect yourself from lightning?
Ans: In order to protect oneself, the shelter should be taken in a house that has a lightning conductor.
(b) How are charges generated?
Ans: When two objects are rubbed against each other, the negative charge on one of the objects is transferred to the other object. Making the second object to acquire negative charge. The first object becomes positively charged due to loss of negative charge.
(c) In the lightning conductor, what provision is made for spreading the electricity into the ground?
Ans:
(i) A lightning conductor consists of a long copper strip, one end of which is forked. The forked end is placed at the highest point of the building.
(ii) The other end of the strip is connected to a plate of cast iron.
(iii) In a pit dug in the ground, coal and salt are filled. The iron plate is placed upright in the pit.
(iv) So provision is also made to pour water into it. This is to help spread the electric charge quickly into the ground and prevent damage.
(d) Why do farmers stick an iron staff into the ground while working in the field in rainy conditions?
Ans:
(i) The lightning conductor is a device intended for protection from a lightning strike.
(ii) Whenever an electrically charged cloud passes over the building, the electric charges try to flow towards the building due to the difference in their charge.
(iii) The clouds have a negative charge, while the building has a positive charge.
(iv) The force of attraction thus acts, and the lightning may fall on the building.
(v) But these currents are conducted into the ground through the copper strip of the lightning conductor. The damage to the building is thus prevented.
(vi) When such a lightning conductor is fixed on a tall building, the surrounding area is also protected from lightning.
(vii) An iron staff works like a lightning conductor. Hence, farmers stick an iron staff into the ground while working in the field in rainy conditions.
(e) Why is lightning not seen everyday during the rainy season?
Ans: When there is electric charge produced on a very large scale, then only there is the possibility of lightning. Rest of the time such conditions may not be there. Therefore, lightning is not seen every day during the rainy season.
4. What are the characteristics of a static electric charge?
Ans: Characteristics of static electric charge:
(i) The charge is developed only when friction occurs.
(ii) The charge developed after rubbing two unlike objects is equal and of different types (positive and negative). The combined total of both charges is zero.
(iii) The static electric charge is of short duration.
5. What is the damage caused by lightning? How will you create awareness to prevent it?
Ans:
(i) Damage caused by lightning:
There is great damage to the trees, buildings, etc. The trees burn, and the property is destroyed. The electrical equipment in the house becomes useless.
(ii) Awareness to prevent damage:
One should not move out of the house when there is thunder and lightning. People should be made aware of their safety during such times. They should not go into the water. One should not stand under a tree or go to open spaces or heights. Lightning conductors should be installed in all buildings. Disaster management should be known to people.