DAV Class 7 Science Chapter 11 Electric Charges at Rest Question Answer Notes
DAV Class 7 Science Chapter 11 Electric Charges at Rest Question Answer Notes Solution by Expert Science Teacher. DAV Class 7 Science 11th Chapter Electric Charges at Rest for Students of DAV Schools.
Lesson No 11
Electric Charges at Rest
A.) Fill in the blanks.
Answer: (1) two (2) Like, attract (3) charged, conductors (4) thunder (5) Benjamin Franklin
B.) Write True or False for the following statements.
Answer: (1) False , it isn’t equal or similar charges (2) True (3) True (4) True (5) False, we need a lightning pole or lightning conductor.
C.) Tick the correct option.
Answer:
1.) move away from comb B
2.) B
3.) either attract or repel each other.
4.) only the earth that ‘shares its charges, with the object to be charged.
5.) decreases in the first case but remains unchanged in the second case.
6.) either between two opposite charged clouds or between a charged cloud and the ground.
D.) Answer the following questions in brief.
2.) Name two objects (a) that can be charged by rubbing (b) that do not get charged on rubbing.
Answer: (a) Two objects that can be charged by rubbing are a balloon and a Styrofoam cup.
(b) Two objects that do not get charged on rubbing are glass and plastic.
3.) State the main difference between a conductor and an insulator.
Answer: The main distinction between a conductor and an insulator is that the former allows the movement of heat and electricity while the latter does not. While conductors are often made of metals such as copper, aluminium, as well as silver, insulators are typically made of materials like plastics, foam, and glass.
4.) Name the device used for protecting tall buildings from lightning strikes.
A lightning pole is a device that is used to divert lightning strikes from tall structures. A lightning rod is a steel structure with a link to the soil that is placed at the highest point of a building. The lightning rod reduces the likelihood of harm to the building as well as its inhabitants by reconfiguring the power surge towards the structure.
5.) Give the meaning of the term ‘earthing.
Answer: Earthing is the practise of connecting electrical systems to the ground, or Earth, in order to reduce the risk of receiving an electric shock. To do this, an electrical system as well as circuit is connected to a conducting plate or rod that is buried in the ground. This allows any additional energy to travel into the earth rather than through a living thing.
6.) List down two precautions that a person can take if he is caught outside in the open during a lightning strike.
- Avoid high ground.
- Avoid metal objects.
E.) Answer the following questions.
1.) A charged drinking plastic straw is brought near another suspended plastic straw, that is (a) similarly charged (b) uncharged. Explain what we would observe in each case and why.
Answer: Case A: The two plastic products will resist one another if their charges are comparable. Since as charges repel one another, this occurs. The two straws will be pushed apart by the strong electrostatic force between them.
Case B: The 2 plastic straws will not communicate with one another if they are not charged. This is so that charges can only interact when their signs are in opposition. As a result, there won’t be any electrostatic attraction between the two straws, and they’ll stay in their original places.
2.) Why do we say that ‘charges are always produced in pairs’?
Charges have always been produced in pairs as a result of the conservation of charge law. This law states that for the total charge in a closed system to stay unchanged, each charge produced must be countered by a force that is both equal to something and opposite to it. This shows that when a force is generated, two charges are produced: a positive charge and a negative charge. The concept of charge conservation explains why charges are always created in pairs. For instance, when a cell is plugged into a circuit, positive and negative charges are produced at the circuit’s opposing ends.
3.) Describe a simple experiment to show that the total charge on a pair of objects, that have been rubbed together, is zero.
Electrons are transported between charged things when they come into contact. The term “charging via conduction” is used to describe this electron transfer process. Electrons transfer from the more highly charged item to the less highly charged item when two charged objects come in contact. The more highly charged item loses its surplus charge when the electrons migrate, while the less highly charged item picks up a charge. The more electrically charged object progressively returns to neutral charge as this process continues until the two objects have the same electrical charge. In other words, when an electrically charged object makes contact with another object, it loses its energy because the electrons it was holding onto are transferred to the other object.
4.) Why does a charged object lose its charge when touched?
When a charged object comes into contact with another object, the two objects share electrons. This process of electron transfer is called “charging by conduction.” When the two objects touch, electrons move from the more highly charged object to the less highly charged object. As the electrons move, the more highly charged object loses its excess charge, and the less highly charged object gains a charge. This process continues until the two objects have equal amounts of charge and the more highly charged object returns to a neutral charge. In other words, when a charged object is touched, it loses its charge because the electrons it has been holding onto are passed onto the other object.
5.) Can we say that a charged object attracts an uncharged object by first charging it through induction? Explain your answer.
Answer: It is untrue that induction may draw an uncharged object to a charged one. Induction occurs when a charged object is brought close to an uncharged object. In this case, the charged object will produce an electric field that will charge the uncharged object. This phenomenon is known as electrostatic induction. The charged object has not necessarily been attracted to the uncharged one, nevertheless, according to induction. The electric current of the charged object is the only thing that has caused the previously uncharged object to become charged.
5.) Can we say that a charged object attracts an uncharged object by first charging it through induction? Explain your answer.
The idea that induction may attract an uncharged item to a charged one is incorrect. This is because induction requires that an electric charge be transmitted from one object to another, which cannot be done by an object that is not charged. Induction is the technique by which an electric field can create a voltage in a wire without coming into contact with the source of the electric field. An electric current is created when electrons move through a conductor, altering the electric field that surrounds it. Electromagnetic induction is the term for this process.
6.) State the sign of the charge acquired by an object when it is charged, by a positively charged rod, through (a) conduction (b) induction. Give the reason for your statement.
Conduction: An object will become negatively charged when it conducts a positive charge from a rod. This is due to the object’s negatively charged electrons being drawn to the positively charged rod. The object now has a net positive charge overall as a result of the electrons moving from it to the rod.
Induction: An object will become positively charged when it gets a charge by induction from an electrode surface rod. This is caused by the division of charge that takes place in the object when the rod is placed close to it. The rod gives the thing a positive charge by attracting the negative charge and repelling the positive charge.
7.) Is it important to have a very good contact between the lower end of a lightning conductor and the earth? If so, why?
The only safe way to send the energy of a lightning strike away from a building or other structure and into the ground is to have very good connection between the low end of a lightning conductor’s scale and the earth. The grounding electrode, which is located at the bottom of the lightning conductor, is connected to the earth using a grounding rod or other suitable grounding device. The lightning strike can be guided away from the building and toward the surface, where it can safely release its energy, thanks to this link to the soil. Without this link, it wouldn’t be possible to safely divert the lightning strike away from the structure, which could result in significant damage.
More Extra Questions for Preparation
Q.1.) Fill in the blanks.
1.) Repulsion when two charged up objects are similar in nature.
2.) Unlike charges attract each other.
3.) The process of transfer of charge to the earth is called earthing.
4.) Lighting strikes on the surface of earth about 100 times every second.
Q.2.) True or false.
1.) Unlike charges repel each other.
Answer – False
2.) Metallic materials are known as conductors.
Answer – True
3.) Glass rod is non metallic.
Answer – True
4.) Plastic comb does not charged up on rubbing.
Answer – False
Q.3.) Classify metallic and non metallic materials.
Ebonite rod, metal pen, plastic comb, metal comb, glass rod.
Metallic materials – Metal pen, Metal comb
Non metallic materials – Ebonite rod, plastic comb, glass rod
Q.4.) MCQ “s.
1.) are insulators.
a.) Non metallic
b.) Metallic
c.) Both a and b
d.) None of these
Answer – a.) Non metallic
2.) A plastic scale on rubbing against a woollen cloth gets .
a.) Attracts tiny pieces of paper
b.) Charged up
c.) Both a and b
d.) Only a
Answer – c. Both a and b
Q.5.) Match the following.
1. Drinking water | a. Elektron |
2. UPS | b. Attraction |
3. Amber | c. Charge on a body |
4. Unlike charges | d. Non metallic |
5. Gold leaf electroscope | e. Uninterrupted power supply |
Answer – 1- d, 2 – e, 3 – a, 4 – b,5 – c.
Q.6.) What are Conductors and Insulators?
Answer – Conductors – Metallic material that do not get charged on rubbing are called conductors.
Insulators- Non metals that normally get charged up on rubbing are called insulators.
Q.7.) When object is said to be electrically charged?
Answer – An object is said to be electrically charged if it has acquired the property of attracting light objects.
Q.8.) Explain positive and negative charges.
Answer – Positive charge – The unknown charge is positive if it is repelled by a charged up glass rod.
Negative charge – It is negative if it is attracted by a charged up glass rod.
Q.9.) Write method of charging up.
Answer – Methods of charging up are-
a.) Charging by rubbing or friction.
b.) Charging by contact or conduction.
c.) Charging by nature.
Q.10.) What precautions are taken during lightning?
Answer – a.) Avoid contact with water.
b.) Do not use electric equipments.
c.) Avoid sheds and open areas.
d.) Do not use corded phones.
e.) Stay away from trees.
Q.11.) Write advantages of lightning.
Answer – a.) Lighting converts nitrogen into oxide which gets dissolved in water and come down with rain.
b.) This helps plants to get their much needed nitrogen out compounds.
c.) Lightning can also result in the formation of ozone from oxygen.
d.) Ozone provides a protective blanket in the atmosphere that shields us from the harmful ultraviolet radiation of the sun.
Q.12.) Write types of materials in nature.
Answer – Types of materials in nature are
1.) That gets charged up on rubbing.
2.) That does not get charged up.