Chapter 12
Electricity and Circuits
Exercise
I. Answer the following questions in brief:
Q.1 How does an electric cell produce electricity?
Ans - Electric cell produce electricity from the chemical stored inside it.
Q.2 How many terminals does an electric bulb have? Can you identify them?
Ans - Electric bulb have two terminals one is positive while the other is negative.
Q.3 Why does a fused bulb not glow?
Ans - In fused bulb the filaments break and current does not pass through it.
Q.4 Is air a conductor of electricity or an insulator? What about the human body?
Ans - Air is a insulator but under certain condition it can conduct electricity. Human body is a good conductor of electricity.
Q.5 Why should the two terminals of an electric cell not be joined directly without connecting them through a device like a bulb?
Ans - The two terminals of the electric cell are never joined together without connecting them thought a switch and a device like a bulb because if we do so the chemical in the electric cell get used up very fast and the cells stops working.
Q.6 How are the terminals of an electric bulb different from those of an electric cell?
Ans - In electric bulb the filament is attached to its two terminals whereas the electricity cell has its two terminals one is called positive while other is called negative.
Q.7 Give any two uses of insulators.
Ans - (a) Insulators are used for covering wires switches
(b) Insulators are used to make hand gloves to hold electrical appliances
II. Give one term for each of the following:
a) Device to break or complete a circuit - Switch
b) Materials which allow electric current to pass through them. - Conductor
c) Path of electricity to pass - Circuit
d) Thin wire inside electric bulb which glows when current passes through it - Filament
e) Ends of electric bulb or cell. - Terminals
f) Materials which do not allow electric current to pass through them. - Insulators
III. Fill in the blanks:
a) A torch bulb has an outer case of glass that is fixed on a metallic base.
b) The bulb glows only when current flows through it.
c) A switch is a simple device that either breaks the circuit or complete it.
d) An electric all produces electric from the chemicals stored inside it.
e) When the filament of a bulb breaks, it is said to be fused
f) Both the electric cell and bulb have two terminals each.
IV. State whether True or False
a) An electric bulb has two terminals: one is positive (+) and the other is negative (-). True
b) Human body is an insulator. False
c) The filament of a bulb is made of thick wire. False
d) Handles of a screw driver can be made of metals instead of plastic. False
e) Pure water is an insulator. False
f) We should never join the two terminals of an electric cell directly without connecting them through an electric device. True
V. Match the following:
a) Rubber - (iv) Insulator
b) Cell - (vi) Positive and negative terminals
c) Switch - (i) Make or break circuit
d) Bulb - (iii) filament
e) Metal - (ii) conductor
VI. Select the Correct alternative:
(i) Gucci and Ricci set up the following apparatuses for showing how a switch works in an electrical circuit. Both the set ups were same except in one way. Gucci used a plywood base while Ricci used an iron base.
Which of the following are true?
Ans (d) Gucci's set up is correct while that of Ricci is not
(ii) Which of these is a conductor?
a) Human body b) Air Metal c) Water d) All of these
Ans (d) All of these
(iii) For making electrical wires, we use the materials which are
Ans (a) conductors
(iv) While demonstrating the working of an electric circuit, the bulb does not glow. This may be because
Ans (d) any of these
(v) Electric current flows
Ans (b) From positive terminal to negative terminal
(vi) The handles of screw drivers are made of
Ans (c) any of these
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