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STATIC ELECTRICITY
✔ ) the most appropriate answer.
I. Tick (✔
1. When an ebonite rod is rubbed with fur, the charge acquired by the
fur is:
(a) negative
(b) positive
(c) both positive and negative (d) none of these
2. When a negatively charged body is brought near a suspended
positively charged ball, the ball gets:
(a) attracted
(b) repelled
(c) stay at same place
(d) none of these
3. Aluminium metal is a:
(a) good conductor of electricity (b) magnetic substance
(c) bad conductor of electricity (d) bad conductor of heat
4. A positively charged body has:
(a) excess of electrons
(b) deficiency of electrons
(c) no change in number of electrons
(d) none of these
5. When an uncharged conductor gets electrically charged when
brought near a charged body the process is called
(a) conduction (b) convection (c) induction (d) none of these
6. When a glass rod is rubbed with silk, both glass rod and silk :
(a) acquire equal and similar charges
(b) acquire equal and opposite charges
(c) acquire unequal and similar charges
(d) acquire unequal and opposite charges
Ans. 1. (b)
2. (a)
3. (a)
4. (b)
5. (c)
6. (b)
II. Fill in the blanks.
1. Cat’s skin acquires __________ charge, when rubbed with ebonite
rod, because its electrons are transferred to __________ rod.
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2. Similar charges ____________ each other, whereas opposite
charges _________ each other.
3. It is ______________ electrons in the outermost ______________
of an atom, which are responsible for electrification.
4. When a negatively charged body is placed in contact with the
_____________ charged disc of G.L.E. its ___________ diverge.
5. In an atom number of ___________ is equal to number of electrons.
6. An uncharged insulator can be charged by _______________ with
another body.
7. An uncharged conductor can be charged by ______________.
8. ______________ is the surest test of electrification.
9. A G.L.E. can be charged ________________ by touching a charged
glass rod with its cap.
10. A negatively charged body has ______________ of electrons.
11. The process of charging objects like glass and amber is known as
___________.
12. Ebonite rod acquires ______________ charge when rubbed with
wool.
13. A body which has lost electrons becomes ______________.
14. ______________ is an instrument used for testing whether a body
is charged or not.
15. _____________ is a device that protects buildings from a lightning
strike.
16. ______________ is used in the chimneys of factories to prevent
air pollution.
17. A glass rod is rubbed with silk, the charge on the glass rod is
____________ and the charge on the silk is _____________ .
18. An ebonite rod is rubbed with fur. The charge on the ebonite rod is
___________ and the charge on the fur is ______________.
Ans. 1. Positive, ebonite
2. repel, attract
3. free, shell
4. negatively, leaves
5. Protons
6. rubbing
7. induction
8. repulsion
9. positively
10. excess
11. electrification 12. negative
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13. positively charged 14. electroscope
15. lightning conductor 16. electrostatic precipitator
17. positive, negative
18. negative, positive
III. Statements given below are incorrect. Write correct statements.
1. Glass wool is good conductor of electricity.
Ans. Glass wool is bad conductor of electricity.
2. positive electrification is due to the excess of electrons.
Ans. Positive electrification is due to deficiency of electrons.
3. When silk is rubbed with glass, the silk gets positively charged.
Ans. When silk is rubbed with glass, the silk gets negatively charged.
4. Similar charges attract each other.
Ans. Similar charges repel each other.
5. When ebonite rod is rubbed with wool, they get oppositely charged
due to induction.
Ans. When ebonite rod is rubbed with silk, they get oppositely charged
due to conduction.
6. Lightning conductor always develops the similar charges as is the
charge in the clouds.
Ans. Lightning conductor always develops the opposite charges as is the
charge in the clouds.
7. A gold leaf electroscope can be charged by both conduction only.
Ans. A gold leaf electroscope can be charged by conduction and induction.
8. The electrons flow from a positively charged body to negatively
charged body when connected with a copper wire.
Ans. The electrons flow from a negatively charged body to the positively
charged body when connected with a copper wire.
9. The fur gets negatively charged because of deficiency of electrons.
Ans. The fur gets negatively charged because of excess of electrons.
10. Bad conductors have excess of free electrons.
Ans. Good conductors have excess of free electrons.
11. Similar charges attract each other and opposite charges repel each other.
Ans. Similar charges repel each other while opposite charges attract each
other.
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12. An uncharged electroscope can tell us the nature of charge on a
body.
Ans. A charged electroscope can tell us the nature of charge on a body.
13. Lightning is caused due to discharge of similar charged clouds.
Ans. Lightning is caused due to discharge of oppositely charged clouds.
14. Lightning do not strikes at high rise buildings.
Ans. Lightning strikes at high rise buildings.
15. An insulator allows readily an electric current to pass through it.
Ans. A conductor allows readily an electric current to pass through it.
IV. (a) Match the columns.
Column A
Column B
1. Electric current
(a) unit of current.
2. Conductor
(b) device that prevents
a circuit from overheating
3. Insulator
(c) flow of electrons along
a conductor.
4. Ampere
(d) substance which allows
electricity to pass through it.
5. Fuse
(e) non-conductor.
Ans. 1. (c), 2. (d), 3. (e), 4. (a), 5. (b)
(b)
Column A
Column B
1. Two similar charges
(a) acquires a positive charge
2. Two dissimilar charges
(b) insulator
3. When a glass rod is rubbed
with silk, it
(c) conductor
4. When an ebonite rod is rubbed
with fur, it
(d) acquires a negative charge
5. Silver
(e) repal each other
6. Sulphur
(f) attract each other
Ans. 1. (e), 2. (f), 3. (a), 4. (d), 5. (c), 6. (b)
V. Find the odd one out. Give a reason for your choice.
1. Mica, copper, wood, shellac, sealing wax.
Ans. Copper. Copper is a conductor while mica, wood, shellac and sealing
wax are insulators.
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2. Mercury, sulphur, graphite, copper.
Ans. Sulphur. Sulphur is an insulator while mercury, graphite and copper
are conductors.
3. Induction, conduction, magnet, charged body.
Ans. Magnet. Induction, conduction and charged body are all related to
static electricity while magnet is not.
4. Mercury, graphite, oxygen, human body, steel.
Ans. Oxygen. Oxygen is an insulator while mercury, graphite, human body
and steel are conductors.
5. Sulphur, rubber, wood, hydrogen, iron.
Ans. Iron. Iron is a conductor while sulphur, rubber, wood and hydrogen
are insulators.
6. Electron, atom, proton, neutron.
Ans. Atom. An atom is the smallest unit of an element, which may or may
not have an independent existence, but always take part in a chemical
reaction. Atom is made up of electron, proton and neutron.
7. Chloride ion, oxide ion, nitride ion, magnesium ion.
Ans. Magnesiumion. Magnesium ion is positively charged ion while
chloride ion, oxide ion and nitride ions are negatively charged ions.
VI. Give reasons for the following.
1. When you touch the metal disc of an electroscope with a charged
glass rod the metal leaves diverge.
Ans. When we touch the metal disc of an electroscope with a charged glass
rod the metal leaves diverge because of the transfer of free electrons.
2. One should not use an umbrella while crossing an open field in a
thunderstorm.
Ans. One should not use an umbrella while crossing an open field in a
thunderstorm because when a charged cloud passes over an
umbrella, it induces a charge in it, and there is an electrical discharge
between an umbrella and the cloud. Which may be very dangerous.
3. In an electroscope the disc, the connecting rod and the leaves are all
made of metal.
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Ans. In an electroscope the disc, the connecting rod and the leaves are all
made up of metals because metals are good conductors of electricity.
4. The metal wires in the bottom part of the electroscope are earthed.
Ans. The metal wires in the bottom part of the electroscope are earthed
because if there is any charge inside the bottle, it immediately flows
to the earth making the inside of the bottle neutral.
5. The diverging leaves of a charged electroscope collapse, the moment
you touch the disc of the electroscope with your finger.
Ans. The diverging leaves of a charged electroscope collapse, the moment
you touch the disc of the electroscope with your finger because no
electric charge is present on it as the charge will flow from hand to
earth through the body.
VII. State the difference between the following.
1. Proton and electron.
Ans. Proton is a positively charged particle having one unit positive charge
and has a mass almost equal to mass of one atom of hydrogen.
While electron is a negatively charged particle having one unit negative
charge and has a mass of 1/1837 times the mass of one atom of
hydrogen.
2. The charge carried by a glass rod rubbed with silk and charge carried
by ebonite rod rubbed with fur.
Ans. When a glass rod is rubbed with silk, a positive charge develops on
the glass rod and a negative charge is developed on silk. When an
ebonite rod is rubbed with fur, a negative charge develops on ebonite
rod and a positive charge develops on fur.
3. Like charges and unlike charges.
Ans. Like charges repel each other while unlike charges attract each other.
4. Static electricity and current electricity.
Ans. When an electric charge is at rest, it is known as static electricity
when an electric charge is in motion, it is referred to as a current
electricity.
5. Coductors and insulators.
Ans. The substances which have a large number of free electrons such
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that they start drifting from one end of a substance to the other end,
when it is connected to some source of electricity are called
conductors.
While the substances which have a few free electrons, such that
they do not easily drift from one end to the other end, when connected
to some source of electricity are called insulators.
VIII. Answer the following questions.
1. Describe an experiment to show:
(a) Like charges repel each other.
(b) Unlike charges attract each other.
Ans. (a) Experiment to show that like
charges repel each other:
Take a glass rod and rub it with
silk and suspend it freely by a silk
thread. Near this Suspended rod,
bring another glass rod which is
rubbed with silk. It is observed that
suspended glass rod gets repelled.
(b) Experiment to show that unlike
charges attract each other:
Take a glass rod and rub it with
silk and suspend it freely by a silk
thread. Bring near it an ebonite rod
which is rubbed with cat’s skin. It
is observed that glass rod is
attracted by ebonite rod.
2. Briefly describe Rutherford’s structure of atom.
Ans. Rutherford’s structure of atom:
(i) An atom consists of three
subatomic particles neutrons,
protons and electrons.
(ii) Neutron has no charge, proton
has one unit postive charge and
electron has one unit negative
charge.
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3.
Ans.
4.
Ans.
5.
Ans.
(iii) Protons and neutrons form the central core of atom which is
commonly called nucleus.
(iv) The electrons revolve around the nucleus in fixed orbits.
(v) As the atom of a normal element is electrically neutral therefore,
it is believed that the number of protons in an atom is equal
to the number of electrons.
Why does a glass rod get positively charged, when rubbed with
silk? Explain on the basis of electron transfer.
The glass rod transfers its electrons to the silk when it is rubbed
with silk. Thus, glass rod has less number of electrons than the
number of protons in the nucleus. Thus, on the whole, the glass rod
gets positively charged.
Why does an ebonite rod get negatively charged, when rubbed with
fur? Explain on the basis of electron transfer.
Ebonite rod gains electrons from the fur when it is rubbed with fur.
Thus ebonite has more negative charges as compared to positive
charges in the nucleus. Thus, on the whole, ebonite rod gets negatively
charged.
state the mass and charge on
(a) electron
(b) proton
(c) neutron
Charge
(a) Electron 1 unit negative charge
Mass
1/1837 times that of mass
of one hydrogen atom.
(b) Proton 1 unit positive charge Almost equal to hydrogen
atom.
(c) Neutron No electric charge
Almost equal to hydrogen
atom.
6. What are conductors? Define on the basis of structure of atom.
Give four examples of different classes of conductors.
Ans. A substance, which has a large number of free electrons, such that
they start drifting from one end of a substance to the other end,
when it is connected to some source of electricity, is called conductor.
Four examples of different classes of conductors are:
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7.
Ans.
8.
Ans.
9.
(i) Metals: Iron, copper, gold, silver, etc.
(ii) Solution of acids in water: Dil hydrochloric acid, dil nitric
acid, dil sulphuric acid and carbonic acid, etc.
(iii) Solution of alkalies in water: Sodium hydroxide, ammonium
hydroxide, calcium hydroxide, potassium hydroxide, etc.
(iv) Solution of soluble salts in water: Sodium chloride,
potassium nitrate, etc.
What are insulators? Define on the basis of structure of atom. Name
six insulators.
A substance, which has a few free electrons, such that they do not
easily drift from one end of the substance to the other end, when
connected to some source of electricity is called insulator.
For example, alcohol, ether, sugar, starch, wool, fur etc.
How can you use gold leaf electroscope to detect the charge on a
body?
Gold leaf electroscope (G.L.E) is used to detect the charge on a
body.
Take a glass rod and rub it with silk. Touch the rubbed end of the
glass rod with the disc of G.L.E. It is seen that leaf of G.L.E. diverges
outward.
When the glass rod touches the brass
disc of G.L.E, then free electrons from
it flow to the glass rod. This causes a
deficiency of electrons on the brass
disc. To make up for this deficiency
the electrons from leaves flow to
wards the disc. This, in turn, causes
electron deficiency on the leaves. As
leaves are positively charged, they
repel each other, and hence diverge.
Thus, we can say that if a body, on touching disc of gold leaf
electroscope makes its leaves diverge, then that body is charged.
How can you use gold leaf electroscope to detect the nature of
charge on a body?
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Ans. We take a G.L.E. and charge it positively or negatively by touching
its disc with a charged rod. Suppose we have a negatively charged
G.L.E. Now touch the given charged body to the disc of negatively
charged G.L.E.
If the leaves of G.L.E. diverge further,
then the body is negatively charged.
It is because, similar charges repel each
other.
If the leaves of G.L.E. collapse, then
the body is positively charged. It is
because some charges from negatively
charged G.L.E. will flow to the
positively charged body.
10. (a) State the charge present on the glass rod and silk when rubbed
with each other
(b) State the charge present on the ebonite rod and cat’s skin when
rubbed with each other.
Ans. (a) Glass rod gets positively charged and silk gains electrons so
gets negatively charged after rubbing.
(b) Ebonite rod gets negatively charged and cat’s skin gets positively
charged when rubbed with each other.
11. What is an electroscope? Draw a neat diagram of gold leaf
electroscope.
Ans. An electroscope is a device used for detecting electric charges, and
finding the nature of electric charges.
Gold leaf electroscope
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12. What causes thunder and lightning?
Ans. When two clouds carrying opposite charges approach each other, a
charge flows from one to the other through the air. This electrical
discharge which can be seen as a dazzling flash of light is called
lightning.
When lightning occurs the air suddenly gets very hot and expands.
It subsequently cools and contracts. This sudden and tremendous
expansion and contraction of air produces an explosion of loud
sound which is called thunder.
13. Explain how a lightning conductor works?
Ans. A lightening conductor is made of copper rod, on the one end of
which are provided sharp copper points. It is installed on the highest
point of the building. Its lower end is connected to a thick copper
strip which is attached to flat copper plate and buried deep inside
the earth.
When lightning strikes the sharp points of lightning conducto, all the
electric discharge flows into the earth through the copper rod wire,
without damaging the building.
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