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Matter is made up of atoms
Matter is made up of atoms
Experiment l.l
Experiment l.l
Like charges repel; unlike charges attract
Like charges repel; unlike charges attract
Experiment 1.2
Experiment 1.2
Experiment 1.2
Experiment 1.2
Charging by sharing
Charging by sharing
Charging by Contact
Charging by Contact
Charging by Contact
Charging by Contact
A charged object discharges easily when the air contains more ions
A charged object discharges easily when the air contains more ions
Objects are classified as electrical conductors (
Objects are classified as electrical conductors (
Charge distribution
Charge distribution
Charging by induction:
Charging by induction:
Charging by induction:
Charging by induction:
Negative charges are induced on the side closer to the rod and
Negative charges are induced on the side closer to the rod and
I understand now
I understand now
I know the same phenomenon can be observed when a charged rod is
I know the same phenomenon can be observed when a charged rod is
Section 3 Applications of electrostatics
Section 3 Applications of electrostatics
Electrostatic precipitation
Electrostatic precipitation
Electrostatic hazards
Electrostatic hazards
#Flying aeroplanes and moving vehicles accumulate charges too
#Flying aeroplanes and moving vehicles accumulate charges too
#Charges accumulated in clouds are carried to the earth through
#Charges accumulated in clouds are carried to the earth through
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1ELECTROSTICS. 171.11 An uncharged sphere becomes negative
2WHY? When I was a primary student,my after touching negatively charged sphere.
teacher told me to rub my plastic ruler by 18Dsicharging through air. Air contains
using a piece of cloth. As a result, the positive ions and free electrons. When a
ruler attracted pieces of small paper positively charged rods is left in the
automatically. air, the rod gradually attracts free
3Section 1 Electric charges and forces. electrons into it. The positive charge is
4Matter is made up of atoms. An atom then neutralized by the electrons. When a
contains positive charges and negative negatively charged rod is left in the air,
charges. The negative charges are due to the excess electrons are gradually lost
the electrons. The atom as a whole is into the air and neutralize the positive
neutral; the quantity of positive charge ions. In both cases, the rod is said to
and negative charge are equal. There is discharge through air. -. +. -. +. -. + +
empty space. The electrons are easily to + + +. - - - - -. +. -. +. -. +. *Fig
lose away. 1.12. Positive rod. Negative rod. Positive
5Electrons can be transferred from one ions and free electrons in air.
atom to another. When an electron is 19A charged object discharges easily
removed from a molecule, the molecule when the air contains more ions. This can
contains more positive charges than be done by heating the air with a
negative charges. In other words, it flame(Fig l.12) or hot body, or
contains net positive charges . It becomes irradiating it with a radioactive source.
a positive ion (??). +. Positive ion. In these processes, many ions and free
Neutral Atom. electron. electrons are produced. A charged object
6When an electron is added to an atom, also discharges more easily when the air
the atom contains more negative charges contains a lot of moisture. It discharges
than positive charges. It has a net less easily when the air is dry. *Fig
negative charge. We say the atom is 1.12.
negatively charged; it becomes a negative 20Section 2 Conductors and insulator.
ion. +. Negative ion. Electron. Neutral 21Objects are classified as electrical
Atom. conductors (??) or insulators (???). In a
7The quantity of electric charge is conductor, the charges can move easily
expressed in the unit coulomb (C). An from one place to another. On the hand, in
electron carries a charge of e = -1.6 x 10 an insulator, the charges cannot move
-19 C The negative sign means the charge easily. Electrons are free to move in
is negative. -19. conductor. *Fig 2.1.
8Experiment l.l. Charging by friction. 22Conductors and insulators are not two
Rub two acetate strips with a dry woolen distinct class of material. Good
cloth and hold them side by side. The insulators are bad conductors and vice
strips repel each other. Repeat with two versa. Even the best insulator can allow a
rubbed polythene strips. The strips also very small flow of charge. Similarly,
repel each other.(Fig 1.4) Repeat with an charges are not completely free in a
acetate strip and polythene strip. The conductor. Metals are the most common
strips attract each other. conductors while non-metals are usually
9Discussion of Experiment 1.1. Before insulators. Some common conductors and
an acetate strips is rubbed, it contains insulators are listed below. Conductors.
the same quantity of positive and negative Insulator. Silver copper aluminium
charges. The strip is neutral because graphite water. Vacuum plastics wax dry
there is no net charge. The same is true air wood. Earth, human body. In decending
for the woolen cloth. When the acetate order of goodness.
strip is rubbed, some electrons in the 23Charge distribution. For a conducting
strip are transferred to the cloth . As a sphere, the excess charges settle evenly
result, the strip contains more positive on the surface (Fig 2.2). For a conductor
charges than negative charges. It has a of irregular shape, the charge density is
net positive charge. On the other hand, higher at sharp points. *Fig 2.2 It is the
the cloth is negatively charged because it same of positive ions.
contains more negative charges than 24Charging by induction. The
positive charges. When a polythene strip distribution of charges on a conductor is
is rubbed, it is negatively charged while also affected by charges outside. Fig 2.3
the cloth is positively charged. Some shows a charged rod (which may be a
electrons in the cloth have been conductor or an insulator) brought near a
transferred to the strip. neutral conductor. The positive charges in
10Like charges repel; unlike charges the rod attract unlike charges in the
attract. Different material strips attract conductor to the side closer to the rod
each other. Same material strips repel and push the like charges to the far side.
each other. *Fig 1.5. There are forces The conductor is charged locally. But on
called electric forces (??), which cause the whole it still remains neutral. This
the strips repel or attract each other. phenomenon is called electric induction
11In all cases, no new charges are (???). The charges separated in the
produced in the rubbing process. The conductor are called induced charges. The
charges are merely separated. They are more charges the cod contains and closer
transferred from one object to the other is the rod to the conductor, the more
through direct contact of the two objects. charges are induced. rod. + + + +. -. -. -
The quantity of charge obtained by one -. ++. + +. conductor. *Fig 2.3.
object is equal to the quantity of 25Charging by induction: Alternatively,
opposite charge obtained by the other. The *Fig 2.4. *Fig 2.5.
net charge of the two objects taken 26Negative charges are induced on the
together remains zero. Charge cannot be side closer to the rod and positive
created or destroyed. Principle of charges on the far side. The attractive
conservation of charge. force between the positively charged rod
12Experiment 1.2. Experiment 1.2. and the negative charges on the aluminium
Charging by pushing. Connect one strip to piece is larger than the repulsive force
the positive terminal and the other to the between the rod and the positive charges.
negative terminal (Fig 1.7). The strips As a result, there is a net attractive
attract each other. Connect two aluminium force between the rod and the aluminium
strips to the positive terminal of the piece. *Fig 2.6 The pieces are attracted
extra high tension (EHT) power supply as towards the rod. Attraction of neutral
shown below. The strips repel each other. objects.
*Fig 1.6. *Fig 1.7. 27I understand now. Thank you! *Fig 2.7.
13When both strips are connected to the For the same reason, tiny paper strips are
positive terminal, the EHT power supply attracted towards a charged object.
draws electrons from the strips, which 28I know the same phenomenon can be
then become positively charged. For observed when a charged rod is brought
simplicity, we may say that the EHT power near a stream of running water.
supply pushes positive charges onto the 29Section 3 Applications of
strips. When the strips are connected to electrostatics.
different terminals, the power supply 30Electrostatic precipitation. *Fig 3.1.
pushes positive charges onto one strip 31Photocopying. *Fig 3.2.
through the positive terminal and negative 32Electrostatic hazards. Static charges
charges onto the other strip through the accumulate easily on insulators due to
negative terminal. The charge are friction. This causes a nuisance in many
transferred by conduction. Discussion of respects. ~ When you comb your hair on a
Experiment 1.2. dry day. You can feel the pull on you hair
14Charging by sharing. Experiment 1.3. by the static charges produced. No need to
*Fig 1.7. mention this point!! *Fig 3.3.
15The Van de Graff generator generates 33#Flying aeroplanes and moving vehicles
charges. The Hairs share the same type of accumulate charges too. Aeroplanes are
charge with the generator by conduction. fitted with conductive tyres so that the
Discussion of Experiment 1.3. charges are carried to the earth upon
16Earthing. Fig 1.8 shows a charged landing. If not, a spark may occur during
metal ball electrically connected to the refuel and may cause fires and even
ground. This can be done by connecting the explosions. Oil trucks prevent such
metal ball and the ground with a wire, or accidents by carrying a conductive belt or
simply by touching the ball with the metal chain touching the ground.(Fig 3.4).
finger. Since the earth is a huge object, *Fig 3.4.
it practically obtains all the charges 34#Charges accumulated in clouds are
from the ball, which then becomes neutral. carried to the earth through lightning
In fact, any charged metal will be during a thunderstorm. To prevent the
completely discharged as result of lightning from hitting tall buildings,
earthing or grounding. +. +. +. +. *Fig lightning conductors (???) are installed
1.9 Symbol for earth. *Fig 1.8. ground. on the rooftop. Help! *Fig 3.4 The
17Charging by Contact. *Fig 1.10 An lightning conductor is a lonfg copper
uncharged sphere becomes positive after strip .
touching positively charged sphere. *Fig 35THE. END.
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