Solution-Class 7-General Science-Chapter-8-Static Electricity-Maharashtra Board

Static Electricity

Based on Maharashtra Board Class 7th General Science Chapter 8

Solution

Question 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.
(b) ...................... is responsible for generation of electric charge in an object.
(c) A lightning conductor is made of a .................. strip.
(d) .................. does not get electrically charged easily by rubbing.
(e) There is ...................... when opposite electric charge come near each other.
(f) A ..................... can be detected with an electroscope.

Answer :

(a) There is always repulsion between like charges.

(b) Displacement of negative charge is responsible for generation of electric charge in an object.

(c) A lightning conductor is made of a copper strip.

(d) Plastic does not get electrically charged easily by rubbing.

(e) There is always attraction when opposite electric charge come near each other.

(f) A charged object can be detected with an electroscope.

Question 2:

Explain why it is not safe to go out with an umbrella when there is heavy rain, lightning or thunder.

Answer :

  • Generally the central rod of an umbrella is metallic with a pointed tip at the upper extremity. Moreover, the ribs of umbrella are also made up of metals.
  • 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.

Question 3:

Answer in your own words.

(a) How will you protect yourself from lightning?

Answer :

Answer:

In order to protect oneself from lightning:

  • Avoid taking shelter under trees.
  • Avoid being near to any kind of metal objects which may include metal wires, fences, machinery and power appliances.
  • Take the shelter in a house that has lightning conductor.

(b) How are charges generated?

Answer :

Charges are generated in an object when the object loses or gains some electrons.

Methods of generating charges are:

  • Rubbing: When two insulators are rubbed with each other, one of them loses electrons and the other gains electrons. The one which gains electrons gets negatively charged and the other one gets positively charged.
  • Conduction: When a charged body is brought in contact with an uncharged conductor, the conductor gets charged.
  • Induction: When a charged body is brought near to a neutral body say a conductor or an insulator, the electrons and protons in the neutral body gets separated. Thus, the body acquires temporary charge as long as the charged body is kept near it. 

(c) In the lightning conductor, what provision is made for spreading the electricity into the ground?

Answer :

  • Lightning conductor consists of a long copper strip, one end of this is forked. The forked end is placed at the highest part of the building.
  • The other end of the strip is connected to a plate of cast iron.
  • In a pit dug in the ground, coal and salt are filled. The iron plate is placed upright in the pit.
  • Some provision is also done to pour water into it.

This is to help in spreading 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?

Answer :

In rainy conditions, there is very high chance of lightning striking the Earth. So, the farmer by putting an iron staff into the ground while working in the field in rainy condition, makes sure that he and his crops remains safe in case lightning occurs. This is because the iron staff works like lightning conductor and will be more prone to lightning than the crops and his body. Thus, the electric charges from the clouds will flow to the ground through the staff without affecting the plants and farmer in case of lightning during rainy weather.

(e) Why is lightning not seen everyday during the rainy season?

Answer :

When there is electric charge produced on a very large scale, then only there is possibility of lightning. Rest of the times such condition may not be there. Therefore, lightning is not seen every day during the rainy season.

Question 4:

What are the characteristics of a static electric charge?

Answer :

The characteristics of a static electric charge are as follows:

  • The charge is developed only where friction occurs.
  • The charge developed after rubbing two unlike objects is equal and of different types. (i.e. positive and negative). The combined total of both the charges is zero.
  • Like charges always attract each other and unlike charges always repel each other.
  • The static electric charge is of short duration.

Question 5:

What is the damage caused by lightning? How will you create awareness to prevent it?

Answer :

 Damage caused by lightning are:

  • A fire can start if the lightning strike makes contact with flammable material. These can include gas pipes, wood, paper, etc.
  • If lightning follows electrical wiring, then the wires gets overheated which can cause a fire hazard.
  • Lightning can cause damage to walls, concrete, plaster and glass of a building. It can damage the electrical appliances connected to damaged sockets.
  • Lightning can damage tall trees and crops. It can even lead to forest fire.
  • Lightning, if strikes on living beings, can take their lives.

These damages can be prevented if preventive guidelines against lightning is taught to each and every individual.

Awareness to prevent damage :

  • One should not move out of the house when there is thunder and lightning.
  • People should be made aware about the safety during such times.
  • They should not go into the water.
  • One should not stand under a tree or go to the open spaces and heights.
  • The lightning conductors should be installed in all buildings.
  • The disaster management should be known to people.

Main Page : Class 7th MSBSHSE – General Science - All chapters notes, solutions, videos, test, pdf.

Books :  Maharashtra Board-Class 7 Science Text Books – Chapter wise  PDF for download 

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