Question

Here it is written that the pith balls rubbed with plastic rod repel glass rod(3rd line).why it repel glass rod,it should attract it as glass rod is positively and plastic rod is negatively charged!!​

Answer 1

Answer:

Here it is written that the pith balls rubbed with plastic rod repel glass rod(3rd line).why it repel glass rod,it should attract it as glass rod is positively and plastic rod is negatively charged!!

Answer 2

☆observation;

ok,so first you have to read carefully the whole thing,until the last word of that para.

》Here, see these things are done :

• glass rod is rubbed with silk, by the method of friction. One who has higher affinity for electron will take the electron during rubbing and one which has less affinity will lose.
• so silk has high affinity will get negatively charged and glass rod will get positively charged.
• and it get opposite with plastic rod and fur.
• plastic rod= -vely charged, fur = +vely charged.

》Now moving to another method of charging-- Conduction.

• As plastic rod is touched with pith balls, touching means there will be the transfer of charges from one to other.
• so at first during initial touching, one side of pith ball will get filled with +ve charge/deficiency of electrons due to attraction by -ve charge plastic rod.
• by which the charge(electrons) will flow from high to low, plastic rod to pith ball.
• results, negatively-charged pith balls.
• as both pith balls are also touched so they both will have -ve charge.

☆So the plastic rod and pith balls will repel due to like charges(-ve).

》Now returning to your actual question;

•please don't get confused by their incomplete lines!!

• So the next step they do is taking a glass rod and a new pith ball(which is neutral).
• and doing the same experiment as they had done with plastic rod and pith ball.
• so here the same as above due to conduction the pith ball = +vely charge , same as glass rod.
• And after conduction when we bring both of them, they will obviously get repelled (due to like charges).

》Now, they get more sure for the experiment by doing;

• So we have two kind of pith balls:

1. get charged by plastic rod= -vely ball.
2. get charged by glass rod = +vely ball.

And if we bring these two ball together, they will..??

---Attract(due to unlike charges)

☆☆And this is their dramatic observation which they ended their explanation.

And also see the attachment, 1st is of charging methods used between plastic and pith ball, which i'd explained.

2nd attachment is the whole ncert page, of your ques.

• I know your query was due to that pith ball, you probably had thought, it has that initial -ve ball isn't it?
• No, the pith ball taken as new neutral ball.

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so incase i'll know if there is some mistake.

Good luck.