Chapter -8 Electricity
CHECK YOUR PROGRESS PAGE 109
TRUE and FALSE
1. False, When a glass rod is rubbed with silk cloth, the glass rod acquires a positive charge.
2. True
3. False; A conductor held in hand cannot be charged by rubbing it with a silk cloth.
4. False; Two balloons rubbed with hair will repel each other.
5. False; If an object transfers its electrons to another object, it becomes positively charged.
CHECK YOUR PROGRESS PAGE 114
Fill in the blanks
1. charge
2. diverge
3. lightning conductor
4. Lightning
5. conduction, induction
THINK AND ANSWER PAGE 118
A fuse wire has a melting point less than that of connecting wires. This is to ensure that the fuse
wire melts before the connecting wires in case the circuit gets overheated due to overloading or
short circuit.
THINK AND ANSWER PAGE 119
If electrical appliances are not connected to the earth wire, then in case of leakage of current
from the appliance, the undesired current reaching its outer body passes through the person
touching the device, and he gets an electric shock.
Exercises
A. Tick the correct answer
1) c. 2) a
3) b. 4) a
5) b 6)c
7) c 8) a
9) c 10) a
B. Fill in the blanks
1) atom 2) positive
3) charged. 4) negative
5) copper, iron. 6) live
7) earth connector
8) kilowatt- hour
9) short circuit
10) less
C. True and false
1. True
2. True
3. False; The force of attraction or repulsion between two charged bodies is called electrostatic
force.
4. False; The leaves of a gold-leaf electroscope are made of gold.
5. False; Lightning is caused due to discharge between oppositely charged clouds.
6. False; The cables that bring electricity to our homes consist of three wires.
7. False; Electric meter measure the consumption of energy in kilowatt-hours.
8. True
D. Answer the following in short
1. A body is charged by friction whenever two objects are rubbed against each other. Then,
some of the free electrons get transferred from one object to the other. The object that loses
electrons gets positively charged, while the one that gains electrons (lost by the first object) gets
negatively charged.
2. When a glass rod is rubbed with silk, some free electrons from the glass get transferred to the
silk cloth, thus making the glass positively charged and the silk negatively charged.
3. When a positively charged glass rod is brought in contact with a negatively charged
electroscope, the free electrons from the leaves move towards the rod. This decrease in
negative charge decreases the divergence in the gold leaves. Hence, the gold leaves collapse.
4. When an uncharged object is touched with another charged object, the uncharged object also
gets charged. The total charge on the charged object gets equally distributed between the two
objects in contact. The process is called charging by conduction.
5. Earthing of an electrical device refers to the connection of the metal case of the electrical
appliance to to a large metal plate buried deep inside earth, via an earth wire
6. Short circuit is caused due to the contact between the live and the neutral wire because of
defective or loose connections or damaged wiring. This results in a sudden large current flowing
through the circuit.
7. If too many devices connected to the same circuit are operated at the same time, the wires
draw a much larger current from the mains than they can handle. This is called overloading.
8. Two precautions while handling electricity are given below-
a. Do not touch switches or plugs with wet hands.
b. Put off the mains while working on the main cable wiring or installing a new device
G. Answer the following
The diverged gold leaves of the electroscope indicates that the electroscope is charged. When
the rod was brought in contact with the cap of the electroscope, the divergence of the gold
leaves decreased. This means that the rod was charged with a charge opposite to that of the
electroscope.
H.Draw diagrams
1. Refer to Fig 8.12
2. Refer to Fig 8.14
THINK AND ANSWER
1. Dust accumulate on ceiling fans due to the electrical attraction between the blades and dust
particles. As the blades of a fan rotate, they experience frictional forces due to the air around it.
Due to this, the blades of the fan get charged and attract the dust particles in the air.
2. An electroscope is enclosed in a glass jar to protect the gold leaves from the drafts of air
current.
3. In case of a fault, excessive current flows through the earth wire because it provides
conducting path to the earth.
4. A switch must be connected to the live wire so that when it is in OFF position, then the
appliance to which it is connected will be disconnected from the live wire.
If the switch would be connected to the neutral wire, then the electrical appliance will be
connected to the live wire even when the switch is in OFF position. This may cause an electric
shock if a person touches the appliance.
