CBSE-NCERT Solution : ELECTRICITY AND CIRCUITS

CBSE NCERT Solved Question Answer

Q1 List some uses of electricity?
Ans1 We use electricity for many purposes to make our tasks easier. Electricity makes it possible to light our homes, roads, Offices, markets and factories. Electricity is used to run various appliances like television, refrigerator, computers etc.We use electricity to operate pumps that lift water from ground level to roof top tank.
Q2  List the components of an electric circuits?
Ans2 The various components of an electric circuit are bulb, cell, battery, switch and wires.

Q3 What are the uses of an electric cell?
Ans3 Electric cell provides electricity to the bulb of a torch. Electric cell are also used in alarm clocks, wristwatches, transistor radios, cameras and many other devices.

Q4  What does an electric cell look like?
Ans4 An electric cell has a metal cap on one side and a metal disc on other side.

Q5 How many terminals are there in an electric cell?
Ans5 All electric cells have two terminals; positive and negative. The metal cap is the positive terminal of the cell. The metal disc is the negative terminal.

Q6 How does an electric cell produces electricity?
Ans6 An electric cell produces electricity from the chemicals stored inside it. When the chemicals in the electric cell are used up, the electric cell stops producing electricity. The electric cell then has to be replaced with a new one.

Q7 What is filament of the bulb?
Ans7 A thin wire that gives off light is called the filament of the bulb. The filament is fixed to two thicker wires, which also provide support to it.

Q8 How are terminals formed in an electric bulb?
Ans8 One of the thick wires which is supporting filament is connected to the metal case at the base of the bulb. The other thick wire is connected to the metal tip at the centre of the base. The base of the bulb and the metal tip of the base are the two terminals of the bulb. These two terminals are fixed in such a way that they do not touch each other.

Q9 Why does an electric cell and an electric bulb has two terminals each?
Ans9 An electric cell and an electric bulb have two terminals to form an electric circuit.

Q10 What is an electric circuit?
Ans10 An electric circuit is an arrangement which provides a complete path for electricity or current to pass between the two terminals of electric cell.

Q11 What is current?
Ans11 Flow of charges from an electric cell constitutes current.

Q12  What is the direction of electric current?
Ans12 The direction of current is taken to be from the positive to negative of the electric cell.

Q13  When does a bulb glow?
Ans13 When the terminals of the bulb are connected with that of the electric cell by wires, the current passes through the filament of the bulb. This makes the bulb glow.

Q14  What is an electric switch?
Ans14 A switch is a simple device that either breaks the circuit or completes it.

Q15  What are electric conductors?
Ans15 Electric conductors are materials which allow electricity to pass through them. Example of conductors are metals like aluminum and copper, human body etc.

Q16  What are electric insulators?
Ans16 Electric insulators are materials which do not allow electricity to pass through them. Examples of insulators are paper, rubber, glass, wood etc.

Q17  What are the uses of conductors and insulators?
Ans17 Conductors and insulators are equally important to us
.Switches electrical plugs and sockets are made of conductors. On
other, rubber and plastics are used for covering electrical wires, plug tops, switches and other parts of electrical appliances, which people might touch.
Q18   Under what conditions does an electric bulb glow?
Ans18 Conditions necessary for bulb to glow are:
1.   The switch should be closed.
2.   There should not be any break in path of current.
3.   The terminal connections should be proper.
4.   The wire used to make electric circuit should be a conductor.

Q19  What precautions should be taken to make an electric circuit?
Ans19 Following precautions should be taken:
a)    The connections between the terminals of components of a circuit should be tight.
b)    The bulb should not be fused.
c)    The chemicals in an electric cell should not have been used up.
d). There should not be any insulator in path of current.

Q20  Why does a bulb not glow when it is fused?
Ans20 An electric bulb may fuse due to many reasons. One reason for bulb to fuse is a break in its filament. A break in filament of an electric bulb means a break in the path of the current between the terminals of the electric cell. Therefore, a fused bulb does not light up as no current passes through its filament.

Q21  What happens when two or more bulbs are connected
f)  in series
g)  in Parallel.
Ans21 When bulbs are connected in series the glow of bulbs decreases .
When bulbs are connected in parallel the glow of bulb remains the same.

Q22  Draw the diagram of a torch and label its components.
Ans22 Torch has a reflector, plastic casing, slide switch, bulb and electric cells.

Q24  Why do covering of switches, appliances, plugs socket is made of insulator?
Ans24 They are covered with insulators because insulators don’t allow current to pass through them so we don’t get shock if we touch them.

Q25  Write (C) in front of conductors and(I) in front of insulators
a)       Plastic scale  - I
b)       Match stick - I
c)        Iron nail - C
d)       Mica - I
e)        Human body - C
f)        Eraser - I
g)        Thread - I

Q24  What happens when wire used to make circuit is replaced by cotton thread?
Ans24 Thread does not allow current to pass through it.
Therefore, no current reaches the filament of bulb. So the bulb does not glow.

Q25  What happens when we place eraser in path of cell and bulb?
Ans25 Since eraser is insulator it causes a break in path of
current so the bulb does not glow.

Q26 Draw and see in which case does the bulb glows
1.        When the positive of bulb is connected with positive of the cell and negative of bulb is connected with negative of cell. Ans1 The bulb will glow.

2.        When the positive of bulb is connected with negative cell and negative of bulb is connected with positive of cell.
Ans2 The bulb will glow.

3. When the positive of bulb is connected with positive of the cell and negative of bulb is connected with negative of cell but switch is open.
Ans3 The bulb wont glow.