Physics
NCERT QUESTIONS WITH SOLUTIONS
p1.Draw in your notebook the symbols to However, the safety pin is not connected
represent the following components of with one of the drawing pins. Thus, the
electrical circuits: connecting wires, circuit is not complete. Hence, safety pin
switch in the 'OFF' position, bulb, cell, represents a switch in 'OFF' position. The
switch in the 'ON' position, and battery. circuit diagram of the given figure is
Solution shown in the following.
Component
Bulb Cell
of electric Symbol
circuit
Connecting
wires
Switch in Switch
the ‘OFF’ 3. Figure shows four cells fixed on a board.
position Draw lines to indicate how you will
Bulb connect their terminals with wires to
make a battery of four cells.
Cell
Battery
Switch in
the ‘On’
position’ Solution
To make a battery, the negative terminal
Publishing\PNCF\2024-25\LIVE Module\SET-1\NCERT\7th\Physics\3_Electric Current & Its Effects
2. Draw the circuit diagram to represent the of one cell must be connected to the
circuit shown in figure. positive terminal of the next cell. The wire
indicates the manner in which the given
cells should be connected with each other,
as shown in the following figure.
Solution
In the given circuit, one terminal of the
bulb is connected with one terminal of the
cell while its other terminal is connected
to a safety pin.
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NCERT Basics : Class 7
4. The bulb in the circuit shown in Figure 7. Will the compass needle show deflection
does not glow. Can you identify the when the switch in the circuit shown by
problem? Make necessary changes in the figure is closed?
circuit to make the bulb glow.
Solution
Solution No.
The bulb in the circuit is not glowing The given circuit does not have any
because the two cells are not connected current source, In the absence of current,
properly. To make the bulb glow, the
the wire does not behave as a magnet and
negative terminal of one cell should be
hence, the compass needle will not show
connected to the positive terminal of the
other cell, as shown in the given figure. any deflection.
8. Fill in the blanks
(a) Longer line in the symbol for cell
represents its ______terminal.
(b) The combination of two or more cells
is called a_________.
5. Name any two effects of electric current.
(c) When current is switched 'on' in a
Solution
room heater, it gets________.
The two effects of electric current are
(d) The safety device based on the
Publishing\PNCF\2024-25\LIVE Module\SET-1\NCERT\7th\Physics\3_Electric Current & Its Effects
(i) Heating effect of electric current.
(ii) Magnetic effect of electric current. heating effect of electric current is
6. When the current is switched on through called a_________.
a wire, a compass needle kept nearby gets Solution
deflected from its north-south position. (a) Longer line in the symbol for cell
Explain. represents its positive terminal.
Solution
(b) The combination of two or more cells
When a current is switched on through a
is called a battery.
wire, the wire starts behaving as a
(c) When current is switched 'on' in a
magnet. Hence, when a compass needle is
placed near the given current carrying room heater, it gets heated.
wire, it gets influenced by the magnetic (d) The safety device based on the heating
effect of electric current and gets effect of electric current is called a
deflected from its North- South position. fuse.
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Physics
9. Mark 'T' if the statement is true and 'F' if
Hammer Bell (gong)
it is false.
(a) To make a battery of two cells, the Electromagnet
Contact
negative terminal of one cell is
connected to the negative terminal of
the other cell.
Iron armature
(b) When the electric current through the
fuse exceeds a certain limit, the fuse
wire melts and breaks.
Spring Switch
(c) An electromagnet does not attract a
piece of iron. 10. Do you think an electromagnet can be
(d) An electric bell has an electromagnet. used for separating plastic bags from a
Solution garbage heap? Explain.
(a) False : Solution
To make a battery of two cells, the No.
negative terminal of one cell must be Electromagnets can only attract magnetic
connected to the positive terminal of materials. Plastic bag is a non-magnetic
the other cell. material and will not be attracted by an
(b) True : electromagnet. Hence, an electromagnet
The wire of the fuse is made of special cannot be used for separating plastic bags
material which has a low melting from a garbage heap.
point. When large current passes 11. An electrician is carrying out some
through a fuse, it melts quickly and repairs in your house. He wants to replace
Publishing\PNCF\2024-25\LIVE Module\SET-1\NCERT\7th\Physics\3_Electric Current & Its Effects
breaks the circuit. a fuse by a piece of wire. Would you
(c) False : agree? Give reasons for your response.
Working of an electromagnet is based Solution
on the magnetic effect of electric
No.
current. An electromagnet behaves as
The electrician cannot be allowed to
a magnet when current passes
replace the fuse in the house by a piece of
through it. Hence, it will attract a
wire. This is because every wire cannot be
piece of iron.
used as a fuse filament. A fuse filament
(d) True :
must have a low melting point such that it
An electric bell has a piece of iron
could melt and break in response of large
wound by a coil. When current passes
amount of current. Most of the wires have
through this coil, it behaves as an
high melting point.
electromagnet.
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NCERT Basics : Class 7
12. Zubeda made an electric circuit using a 13. In the circuit shown in figure
cell holder shown in figure a switch and
bulb.
When she put the switch in the 'ON' A B C
position, the bulb did not glow. Help
Zubeda identifying the possible defects in
the circuit. (i) Would any of the bulbs glow when the
switch is in the 'OFF' position?
(ii) What will be the order in which the
bulbs A, B and C will glow when the
switch is moved to the 'ON' position?
Solution Solution
One of the reasons may be that the rubber (i) No.
band used in the cell holder may not be When the switch is in 'OFF' position, the
tight enough to keep the two cells in
current does not flow through the circuit.
contact with each other. If the cells are not
in proper contact with each other, then Hence, none of the bulbs will glow.
the circuit will not be complete and (ii) Bulbs will glow simultaneously.
current will not flow through the circuit. When the switch is moved to the 'ON'
Hence, the bulb will not glow. The other
position, then all the bulbs will glow at
reason may be that the two cells are not
once. This is because they all are
connected properly. The negative
terminal of one cell must be connected to connected to the same battery and switch.
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the positive terminal of the other cell.
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