Class-6 Science, Chapter-12 Electricity and Circuits , Additional exercises with solutions in line with NCERT book / CBSE Syllabus


Chapter 12
Electricity and Circuits 
=========================================================
Exercises from textbook
Additional Exercises
Tables from Textbook
Activities/Projects

Additional Exercises


Choose the correct answer:

1.    In an electric cell direction of current is taken to be from
a.    Positive to Negative terminal (√)
b.    Negative to positive terminal
c.     None of them
2.    The thin wire that gives off light in a bulb is called the _____ of bulb.
a.    Terminal
b.    Filament (√)
c.     Fuse
3.    Which of these is not an insulator:
a.    Copper(√)
b.    Rubber
c.     Plastic
4.    A simple device which is used to make or break a circuit is called:
a.    Bulb
b.    Switch (√)
c.    Wire
5.    Which type of energy is generated by an electric cell
a.    Electric (√)
b.    Magnetic
c.    Both
6.    Which of these appliances uses a simple electric circuit?
a.    Electric torch (√)
b.    Air Conditioner
c.    Refrigerator
7.    Positive terminal of an electric cell can be located by seeing _____
a.    Metal cap (√)
b.    Metal disc
c.    Metal cover
8.    Who discovered the electric cell?
a.    Thomas Alva Edison
b.    Alessandro Volta (√)
c.    None of these
9.    A positive and negative terminal are present in ___
a.    Electric Cell (√)
b.    Electric bulb
c.    Both
10. A path along which electric current flows is called:
a.    Electric charge
b.    Electric cell
c.    Electric circuit (√)

 Science Class-7

 Fill in the blanks:

1.    Human body is a conductor of electricity.
2.    Electric cell is a source of electricity.
3.    Insulators do not allow electricity to pass through them.
4.    The bulb glows only when the current flows through the circuit.
5.    An electric bulb does not glow on connecting to cell when the bulb is fused.
6.    The metal disc is the negative terminal of the cell.

State whether the following statements are true or false:
a.    We use electricity for making our tasks easier.                                  (True)
b.    A power station provides us with electricity.                                      (True)
c.     Metal cap is the negative terminal of cell.                                          (False)
d.    Both the electric bulb and the bulb have two terminals each.           (True)
e.    Your body is a conductor of electricity.                                              (True)
f.      Air is an insulator.                                                                               (True)

Distinguish between conductors and insulators.

Conductors
Insulators
The materials which allow electric current to pass through them are conductors of electricity.
 The materials which do not allow electric current to pass through them are called insulators.
For example iron, copper, aluminium
For example rubber, plastic


Answer these questions:

Q. When does an electric cell stop producing electricity?
Ans- When the chemicals in the cell are used up, the electric cell stops producing electricity.Q. Where does the torch get electricity from?
Ans- Electricity to the bulb in a torch is provided by the electric cell.Q. What is a switch?
Ans- A  switch is a simple device that either breaks the current or completes it.

Q. Write uses of insulators?
Ans- Following are the uses of insulators?
(1)  Making seitches, electrical plugs and sockets.
(2) Covering of electrical wires, plug tops, switches and other parts of electrical appliances.


Give reason. Why?

Copper, aluminium and other metals are used for making wires.
Ans- Copper, aluminium and other metals are used for making wires as they are conductors of electricity.

 A fused bulb does not light up.
Ans- A fused bulb does not light up because no current passes through its filament.

We should never join the two terminals of the electric cell without connecting them through a switch and a device like bulb.
Ans-  We should never join the two terminals of the electric cell without connecting them through a switch and a device like bulb. If we do so, the chemicals in the electric cell get used up very fast and the cell stops working.

Handle of an electric iron is made up of ebonite.
Ans-  Handle of am electric iron is made up of ebonite as ebonite is an insulator.

Exercises from Textbook

Fill in the blanks:
1.    A device that is used to break an electric circuit is called switch.
2.    An electric cell has two terminals.


Mark “True” or “False”for the following statements:

1.    Electric current can flow through metals.                                           (True)
2.    Instead of metal wires, a jute string can be used to make a circuit.  (False)
3.    Electric current can pass through a sheet of thermos col.                 (False)


Explain why the bulb would not glow in the arrangement shown in the following figure.



Ans-  The Bulb will be not glow as the current in circuit will not be enough  to glow the lamp due to high resistance in the tester

Complete the drawing shown in figure below to indicate where the free ends of the two wires should be joined to make the bulb glow.

Ans- In the given figure-
(1)  Positive terminal of cell should be connected to the switch.
(2)  The other terminal of bulb should be connected to the other end of switch.

What is the purpose of using an electric switch? Name some electrical gadgets that have switches to build them.
Ans-  The purpose of using an electric switch is to “make” or “break” a circuit. It is also used to divert current from one conductor to another.
Following are some electrical gadgets that have switches to build them:
(a)  Fan
(b)  Electric lamp
(c)   Washing machine
(d)  Mixer Grinder
(e)  Juicer
(f)    TV
Would the bulb glow in the circuit shown in the below figure, if instead of safety pin, we use an eraser.
Ans- No, the current will flow in the circuit, if instead safety pin we use an erase because eraser is a non-conductor of electricity.


Would the bulb glow in the circuit shown in the following figure?

Ans- No, the current will not flow in the circuit in the given figure because here both terminals of cell are connected to same terminal of bulb.

Using the conductor tester on an object, it was found that the bulb begins to glow. Is that object a conductor or an insulator? Explain.
Ans- If the bulb begins to glow on using the conduction tester on an object, it is a conductor. In any circuit current can only flow, if all the components are conductor of electricity.

Why should an electrician use rubber gloves while repairing an electric switch at your home? Explain.
Ans- An electrician should use rubber gloves as a personal protective equipment (PPE). Rubber does not conduct electricity while the human body is a good conductor of electricity.
Rubber glove prevents electrician from shock in case he/she accidently touches naked wires while repairing.

The handles of the tools like screwdrivers and pliers used by electricians for repair work usually have plastic or rubber covers on them. Can you explain why?
Ans- The handles of tools like screwdrivers and pliers used by electricians for repair work must have plastic or rubber covers. This protects user from electric shock in case of accidental contact with current carrying wires/components, as rubber and plastic do not conduct electricity.


Tables from Textbook
Table 12.1 Conductors and insulators
Object used in place of the switch
Material it is made of
Bulb glows? (Yes/No)
Key
Metal
Yes
Eraser
Rubber
No
Scale
Plastic
No
Matchstick
Wood
No
Glass bangle
Glass
No
Iron nail
Metal
Yes
Thermocol
Synthetic polymer
No
Plug top
Plastic
No



Activity / Project
(1)  Imagine there were no Electric Supply for a month. How would that affect your day to day activities and others in your family? Present your imagination in the form of a story or a play. If possible stage the play written by you are your friends in school.

(2)  For your friends, you may set up a game “how steady is your hand?” you will cell, and a half metre long thick metal wire (with its plastic insulation scrapped off) and few pieces of connecting wires. Two nails nearly 1 m apart on a wooden board so that these can be used as a hook. Fix the wire between the nails after inserting it through the loop of the key. Connect one end of this wire to a bulb and a cell. Connect the other terminal of the cell to the key with a wire. Ask your friend to move the loop using the straight wire without touching it. Glowing of the bulb would indicate that the loop of the key has touched the wire.

(3)  Read and find out about Alessandro Volta who invented the electric cell. You may also find out about Thomas Alva Edison who invented the electric bulb.


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