DAV Class 7 Science Chapter 11 Solutions

DAV Class 7 Science Chapter 11 Solutions: DAV Class 7 Science Chapter 11 Electric Charges at Rest Question Answer is provided below to help DAV 7th standard students understand the concepts more effectively.

DAV Class 7 Science Chapter 11 Solutions

Highlights

• A. Fill in the blanks.
• B. True or False.
• C. Tick the correct option.
• D. Answer the following questions in brief.
• E. Answer the following questions.

A. Fill in the blanks.

1. There are ___________ types of charges in nature.

2. ___________ charges repel each other and unlike charges ___________ each other.

3. The materials, that normally do not get ___________ on rubbing, and allow electric current to flow through them with ease, are known as ___________.

4. Lightning and ___________ occur together.

5. The scientist, who proved that lightning is electrical in nature, was ___________.

Answer: (1) two (2) Like, attract (3) charged, conductors (4) thunder (5) Benjamin Franklin

B. Write True or False for the following statements.

1. The charges acquired by a glass rod, and the silk cloth with which it is rubbed, are equal and of the same sign.

2. During charging by conduction, the charged object shares its charge with the uncharged object.

3. A charged body loses its charge if we touch it with our hand.

4. Lightning is a natural electrical discharge phenomenon.

5. We do not need any special device to protect tall buildings from lightning.

Answer: (1) False (2) True (3) True (4) True (5) False

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.

1. A glass rod is rubbed against a silk cloth. Which object/s gets/get charged in this process?

Answer: When a glass rod is rubbed against a silk cloth then both the objects get charged. Glass rod becomes positive charged and Silk cloth becomes negative charged.

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 balloons and plastic scale.

(b) Two objects that do not get charged on rubbing are iron nail and steel spoons.

3. State the main difference between a conductor and an insulator.

Answer: the main difference between a conductor and an insulator are: 

Conductor – substances which allow electric charges to pass through them are called conductors. 

Insulators – substances which do not allow electric charges to pass through them are called insulators.

4. Name the device used for protecting tall buildings from lightning strikes.

Answer: Lightning conductor

5. Give the meaning of the term ‘earthing.

Answer: The process of transfer of charge to the earth.

6. List down two precautions that a person can take if he is caught outside in the open during a lightning strike.

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:

(a) repulsion; because like charges repel each other. 

(b) attraction; because a charged object attracts another unchanged object.

2. Why do we say that ‘charges are always produced in pairs’?

Answer: We say that charges are always produced in pairs because when two objects are rubbed against each other, they both get charged up with equal and opposite amounts of charges.

3. Describe a simple experiment to show that the total charge on a pair of objects, that have been rubbed together, is zero.

4. Why does a charged object lose its charge when touched?

Answer: A charged object lose its charge when touched because when we touch a charged object, the extra charges present on the object get shared with earth through our body.

5. Can we say that a charged object attracts an uncharged object by first charging it through induction? Explain your answer.

Answer:

No, when we bring a charged object near an unchanged object, the two kinds of charges (Already present) in the uncharged object get separated out and opposite kind of charges tend to move towards charged object. Hence unchanged object gets attracted.

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.

Answer:

7. Is it important to have a very good contact between the lower end of a lightning conductor and the earth? If so, why?

Answer:

Yes, it is important to have a very good contact between the lower end of a lightning conductor and the earth because, the lightning charges flow down through it, deep down into the earth and not through the structure. The structure is therefore saved from the damaging effects of lightning.

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