ELECTRIC CHARGE
1.
Answer the following
(a)
Why does friction cause a charge to develop?
Ans:
(1) Friction takes place between two substances.
(2)
Every substance is made up of matter.
(3)
Substances are charge less because of equal number of opposite charges on them.
(4)
Due to friction, negative charge gets transferred from one substance to
another.
(5)
Substance develops positive charge when negative charge is lost, and similarly
substance develops negative charge because of gain of electron.
(b)
Why is charge developed due to friction is called a static electric charge?
Ans:
Charge
developed due to friction remains still on an object, therefore,it is called a
static electric charge.
(c)
Why does the charge developed by induction disappear quickly?
Ans:
(1) This
action of electric charges which takes place when two bodies are brought close
together is called electrical induction.
(2) The negative particles in it get attracted
towards the positively charged body while the positive particles are repelled.
(3) The negative particles collect at that end of
the body which is nearest to the positively charged body, while the positive
particles collect at the opposite end.
(4) Thus, an opposite charge develops on the end
nearest the charged body and a like charge at the furthest end.
(5) if the charged body is removed the charges at
the two ends of the other body mix together again and no charge will remain on
it.
(6) It means that an induced charge exists only so
long as the charged body is placed nearby.
(7) Therefore the charge developed by induction disappear quickly
(d)
Why do leaves of a gold leaf electroscope fly apart when a charged body touches
its disc?
Ans:
(1) When a
glass rod is rubbed on silk cloth, the rod develops a positive (+) charge while
an ebonite rod is rubbed on woollen cloth, a negative (-) charge develops on
the rod.
(2) If a body with no charge is made to touch
the disc of the electroscope the leaves at the other end remain closed.
(3)
But, if a positively or negatively charged body is brought in contact with the
disc, then like charges develop on the leaves and they repel each other and fly
apart.
(4)
The moving apart of the leaves of the electroscope is the test for finding out
if the body is charged.
(e) What causes the crackling sound we hear as we wear a cardigan?
Ans: (1) While putting on a cardigan, it is rubbed
against the hair and the skin on the body.
(2) Due to this there develops static electricity.
(3) since these charges are two unlike charges on the body and on
the wool, they attract each other.
(4) Therefore we hear a crackling sound as we wear a cardigan.
2. Give Reasons.
(a) Ordinarily an atom does not have any charge.
Ans: (1) Each atom contains smaller particles which
are either positively charged or negatively charged.
(2) In an atom they are equal hence they neutralize each other.
(3) Thus ordinarily an atom does not have any charge.
(b) Charge cannot be developed on a metal rod
Ans: (1) Metals are good conductor of
electricity.
(2) copper rod acts as a good conductor.
(3) Therefore charge cannot be developed on a
metal rod.
3.
Fill in the blanks
(a)
The charge on an ebonite rod is negative
(b)
When glass and silk are rubbed on each other, the glass develops a positive charge and the silk a negative one.
(c)
Friction causes the transfer of negative particles.
4.
Match the column
Group
–A Group – B
(a)
Glass rod (2)
Positive charge
(b)
Ebonite rod (3)
Negative chargge
(c)
Lightning conductor (4) Lightning
(d)
Electroscope (1) Charged
body
5.
Write true or false
(a)
When two substances are rubbed on each other, like charges are developed on
each.
Ans:
False (When two substances are rubbed on each other, unlike charges are
developed on each.)
(b)
An atom may have either a positive or a negative charge.
Ans:
False (Atoms are electrically neutral)
(c)
Substances that allow the flow of electricity are called good conductors.
Ans:True
(d)
If the leaves of the electroscope spread only a little, the charge on them is
greater.
Ans: False. (If the leaves of the electroscope spread
only a little, the charge on them is lesser.
