Page 1
46
Curiosity — Textbook of Science for Grade 8
Electricity: Magnetic
and Heating Effects
4
z If we don’t have an electric lamp while making an electric circuit
with an electric cell, is there any other way through which we
can find out if current is flowing in the circuit?
z Is it possible to make temporary magnets? How can these
be made?
z We can generate heat by burning fossil fuels and wood; but how
is heat generated in various electrical appliances?
z How do we know if a cell or a battery is dead? Can all
cells and batteries be recharged?
z Share your questions
?
Probe and ponder
Chapter 4.indd 46 Chapter 4.indd 46 6/28/2025 3:49:31 PM 6/28/2025 3:49:31 PM
Page 2
46
Curiosity — Textbook of Science for Grade 8
Electricity: Magnetic
and Heating Effects
4
z If we don’t have an electric lamp while making an electric circuit
with an electric cell, is there any other way through which we
can find out if current is flowing in the circuit?
z Is it possible to make temporary magnets? How can these
be made?
z We can generate heat by burning fossil fuels and wood; but how
is heat generated in various electrical appliances?
z How do we know if a cell or a battery is dead? Can all
cells and batteries be recharged?
z Share your questions
?
Probe and ponder
Chapter 4.indd 46 Chapter 4.indd 46 6/28/2025 3:49:31 PM 6/28/2025 3:49:31 PM
Chapter 4?—?Electricity: Magnetic and Heating Effects
47
It was the day of the science exhibition, and the school was
buzzing with energy. Mohini and Aakarsh, along with their
friends, went from one exhibit to another, eagerly exploring
different models, asking questions and taking notes. One simple
model really fascinated them. It was a working model of a lifting
electromagnet which was displayed by their senior, Sumana.
In it, instead of a hook like a typical crane, there was an iron
nail wrapped with a wire, which was connected to a battery.
When Sumana closed the circuit, the nail picked up iron paper
clips like a magnet. When she opened the circuit, the clips fell
off. Mohini and Aakarsh, were surprised. They remembered
learning earlier (in the chapter ‘Exploring Magnets’, Curiosity,
Grade 6) that magnetic materials were attracted by magnet and
that iron was a magnetic material. But in Sumana’s model, there
was no magnet, only an electric circuit. They were so excited that
they wanted to try it out themselves.
4.1 Does an Electric Current Have a Magnetic
Effect?
Activity 4.1: Let us investigate
z Collect a magnetic compass, an electric cell, a cell holder,
two drawing pins, a safety pin, two nails, two pieces of
connecting wires (one longer and one shorter), and two
small pieces of cardboard.
z Using two drawing pins, a safety pin, and a cardboard
piece, make a switch (as you made it earlier in the
chapter ‘Electricity: Circuits and their Components’ in
Curiosity, Grade 7).
z Place the cell in the cell holder.
z Fix two nails to a piece of cardboard as shown in
Fig. 4.1a. Fix the middle portion of the longer wire
stretched between the nails, such that it is slightly above
the surface of the cardboard. Attach one end of that
wire to the cell holder and another end to the switch.
z Connect the second wire between the cell holder and
the switch.
z Place the magnetic compass beneath the wire between
the two nails (Fig. 4.1a).
Fig. 4.1: An electric circuit
and a magnetic compass
(b)
(a)
Chapter 4.indd 47 Chapter 4.indd 47 6/28/2025 3:49:32 PM 6/28/2025 3:49:32 PM
Page 3
46
Curiosity — Textbook of Science for Grade 8
Electricity: Magnetic
and Heating Effects
4
z If we don’t have an electric lamp while making an electric circuit
with an electric cell, is there any other way through which we
can find out if current is flowing in the circuit?
z Is it possible to make temporary magnets? How can these
be made?
z We can generate heat by burning fossil fuels and wood; but how
is heat generated in various electrical appliances?
z How do we know if a cell or a battery is dead? Can all
cells and batteries be recharged?
z Share your questions
?
Probe and ponder
Chapter 4.indd 46 Chapter 4.indd 46 6/28/2025 3:49:31 PM 6/28/2025 3:49:31 PM
Chapter 4?—?Electricity: Magnetic and Heating Effects
47
It was the day of the science exhibition, and the school was
buzzing with energy. Mohini and Aakarsh, along with their
friends, went from one exhibit to another, eagerly exploring
different models, asking questions and taking notes. One simple
model really fascinated them. It was a working model of a lifting
electromagnet which was displayed by their senior, Sumana.
In it, instead of a hook like a typical crane, there was an iron
nail wrapped with a wire, which was connected to a battery.
When Sumana closed the circuit, the nail picked up iron paper
clips like a magnet. When she opened the circuit, the clips fell
off. Mohini and Aakarsh, were surprised. They remembered
learning earlier (in the chapter ‘Exploring Magnets’, Curiosity,
Grade 6) that magnetic materials were attracted by magnet and
that iron was a magnetic material. But in Sumana’s model, there
was no magnet, only an electric circuit. They were so excited that
they wanted to try it out themselves.
4.1 Does an Electric Current Have a Magnetic
Effect?
Activity 4.1: Let us investigate
z Collect a magnetic compass, an electric cell, a cell holder,
two drawing pins, a safety pin, two nails, two pieces of
connecting wires (one longer and one shorter), and two
small pieces of cardboard.
z Using two drawing pins, a safety pin, and a cardboard
piece, make a switch (as you made it earlier in the
chapter ‘Electricity: Circuits and their Components’ in
Curiosity, Grade 7).
z Place the cell in the cell holder.
z Fix two nails to a piece of cardboard as shown in
Fig. 4.1a. Fix the middle portion of the longer wire
stretched between the nails, such that it is slightly above
the surface of the cardboard. Attach one end of that
wire to the cell holder and another end to the switch.
z Connect the second wire between the cell holder and
the switch.
z Place the magnetic compass beneath the wire between
the two nails (Fig. 4.1a).
Fig. 4.1: An electric circuit
and a magnetic compass
(b)
(a)
Chapter 4.indd 47 Chapter 4.indd 47 6/28/2025 3:49:32 PM 6/28/2025 3:49:32 PM
48
Curiosity — Textbook of Science for Grade 8
While watching the compass needle, move the switch to
‘ON’ position to allow electric current to flow through the wire
(Fig. 4.1b). What do you observe?
z Now again while watching the compass needle, move the
switch to ‘OFF’ position. What do you observe this time?
z Move the switch between ‘ON’ and ‘OFF’ positions a few more
times. Carefully observe how the compass needle behaves
the each time.
You may have noticed that when the current flows, the compass
needle gets deflected from its original direction. When the current
stops, the needle returns to its original direction.
As we have learnt earlier (in the chapter ‘Exploring Magnets’
in Curiosity, Grade 6), the compass needle is a tiny magnet which
deflects when a magnet is brought near it and this magnetic effect
can act through any non-magnetic materials kept in between.
But why does the compass needle deflect when the current
flows through the wire? The deflection indicates that the current
carrying wire has a magnetic effect on the compass needle.
When the current stops, this magnetic effect disappears and
the compass needle returns to its original direction. The region
around a magnet or a current carrying wire where its magnetic
effect can be felt, such as by the deflection of a compass needle,
is said to have a magnetic field.
When electric current flows
through a conductor (like a wire), it
produces a magnetic field around it.
This phenomenon is known as the
magnetic effect of electric current.
The magnetic field disappears when
the current stops flowing.
Be a scientist
You have just now made the same discovery which
was made by the scientist Hans Christian Oersted
(1777–1851) in 1820, that is, the discovery that
electricity and magnetism are linked. He was a
professor at a university in Denmark. It is said that
once while giving a demonstration, he noticed that
whenever an electrical circuit was closed or
opened, the needle of a magnetic compass, lying
nearby, deflected. He investigated this and when he was certain that
an electric current indeed produced a magnetic field, he published
his findings. This led to other scientists repeating his experiment to
check if they got the same results, and further investigating the
connection between electricity and magnetism.
We have learnt about magnets
and electric current in earlier
grades. I used to think that there
was no link between the two. But
now we found that electricity
and magnetic effect are linked!
Chapter 4.indd 48 Chapter 4.indd 48 6/28/2025 3:49:38 PM 6/28/2025 3:49:38 PM
Page 4
46
Curiosity — Textbook of Science for Grade 8
Electricity: Magnetic
and Heating Effects
4
z If we don’t have an electric lamp while making an electric circuit
with an electric cell, is there any other way through which we
can find out if current is flowing in the circuit?
z Is it possible to make temporary magnets? How can these
be made?
z We can generate heat by burning fossil fuels and wood; but how
is heat generated in various electrical appliances?
z How do we know if a cell or a battery is dead? Can all
cells and batteries be recharged?
z Share your questions
?
Probe and ponder
Chapter 4.indd 46 Chapter 4.indd 46 6/28/2025 3:49:31 PM 6/28/2025 3:49:31 PM
Chapter 4?—?Electricity: Magnetic and Heating Effects
47
It was the day of the science exhibition, and the school was
buzzing with energy. Mohini and Aakarsh, along with their
friends, went from one exhibit to another, eagerly exploring
different models, asking questions and taking notes. One simple
model really fascinated them. It was a working model of a lifting
electromagnet which was displayed by their senior, Sumana.
In it, instead of a hook like a typical crane, there was an iron
nail wrapped with a wire, which was connected to a battery.
When Sumana closed the circuit, the nail picked up iron paper
clips like a magnet. When she opened the circuit, the clips fell
off. Mohini and Aakarsh, were surprised. They remembered
learning earlier (in the chapter ‘Exploring Magnets’, Curiosity,
Grade 6) that magnetic materials were attracted by magnet and
that iron was a magnetic material. But in Sumana’s model, there
was no magnet, only an electric circuit. They were so excited that
they wanted to try it out themselves.
4.1 Does an Electric Current Have a Magnetic
Effect?
Activity 4.1: Let us investigate
z Collect a magnetic compass, an electric cell, a cell holder,
two drawing pins, a safety pin, two nails, two pieces of
connecting wires (one longer and one shorter), and two
small pieces of cardboard.
z Using two drawing pins, a safety pin, and a cardboard
piece, make a switch (as you made it earlier in the
chapter ‘Electricity: Circuits and their Components’ in
Curiosity, Grade 7).
z Place the cell in the cell holder.
z Fix two nails to a piece of cardboard as shown in
Fig. 4.1a. Fix the middle portion of the longer wire
stretched between the nails, such that it is slightly above
the surface of the cardboard. Attach one end of that
wire to the cell holder and another end to the switch.
z Connect the second wire between the cell holder and
the switch.
z Place the magnetic compass beneath the wire between
the two nails (Fig. 4.1a).
Fig. 4.1: An electric circuit
and a magnetic compass
(b)
(a)
Chapter 4.indd 47 Chapter 4.indd 47 6/28/2025 3:49:32 PM 6/28/2025 3:49:32 PM
48
Curiosity — Textbook of Science for Grade 8
While watching the compass needle, move the switch to
‘ON’ position to allow electric current to flow through the wire
(Fig. 4.1b). What do you observe?
z Now again while watching the compass needle, move the
switch to ‘OFF’ position. What do you observe this time?
z Move the switch between ‘ON’ and ‘OFF’ positions a few more
times. Carefully observe how the compass needle behaves
the each time.
You may have noticed that when the current flows, the compass
needle gets deflected from its original direction. When the current
stops, the needle returns to its original direction.
As we have learnt earlier (in the chapter ‘Exploring Magnets’
in Curiosity, Grade 6), the compass needle is a tiny magnet which
deflects when a magnet is brought near it and this magnetic effect
can act through any non-magnetic materials kept in between.
But why does the compass needle deflect when the current
flows through the wire? The deflection indicates that the current
carrying wire has a magnetic effect on the compass needle.
When the current stops, this magnetic effect disappears and
the compass needle returns to its original direction. The region
around a magnet or a current carrying wire where its magnetic
effect can be felt, such as by the deflection of a compass needle,
is said to have a magnetic field.
When electric current flows
through a conductor (like a wire), it
produces a magnetic field around it.
This phenomenon is known as the
magnetic effect of electric current.
The magnetic field disappears when
the current stops flowing.
Be a scientist
You have just now made the same discovery which
was made by the scientist Hans Christian Oersted
(1777–1851) in 1820, that is, the discovery that
electricity and magnetism are linked. He was a
professor at a university in Denmark. It is said that
once while giving a demonstration, he noticed that
whenever an electrical circuit was closed or
opened, the needle of a magnetic compass, lying
nearby, deflected. He investigated this and when he was certain that
an electric current indeed produced a magnetic field, he published
his findings. This led to other scientists repeating his experiment to
check if they got the same results, and further investigating the
connection between electricity and magnetism.
We have learnt about magnets
and electric current in earlier
grades. I used to think that there
was no link between the two. But
now we found that electricity
and magnetic effect are linked!
Chapter 4.indd 48 Chapter 4.indd 48 6/28/2025 3:49:38 PM 6/28/2025 3:49:38 PM
Chapter 4?—?Electricity: Magnetic and Heating Effects
49
The magnetic effect of electric current
has many practical applications, such as
in devices like electromagnets, electric
bells, motors, fans, loudspeakers,
and more.
4.1.1 Electromagnets
Activity 4.2: Let us explore
z Take around 50 cm long length of a flexible
insulated wire, an iron nail, an electric cell, and
few iron paper clips.
z Tightly wrap the wire around the nail in the form
of a coil, as shown in Fig. 4.2, and secure it with
an adhesive tape.
z Connect the ends of the wire to the cell. Take care
to not connect the wires to the cell for more than
a few seconds; otherwise, the cell may weaken
quickly.
z Bring the nail close to the iron paper clips and
lift up. Do the clips hang to the ends of the nail?
z Disconnect the wire from the cell to stop the
flow of electric current in the wire. Do the clips
fall down?
When electric current flows through the coil, the clips cling
to it. But when the current is stopped, the clips no longer cling
to it. Let us now try to investigate these observations in detail
through Activity 4.3.
Activity 4.3: Let us experiment
z Take around 100 cm long flexible insulated wire, a piece
of chart paper, an iron nail, an electric cell, two magnetic
compasses, and few iron/steel paper clips.
z Roll a piece of chart paper to make a cylinder of diameter
roughly equal to the width of a pencil. Secure it with an
adhesive tape.
z Tightly wind around 50 turns of the insulated wire on the
cylinder to form a cylindrical coil as shown in Fig. 4.3a.
Secure the wire with an adhesive tape.
Fig. 4.3: (a) A coil
of insulated wire
Can we use electric
current to make a
magnet?
Fig. 4.2: Coil of wire
connected with a cell
Chapter 4.indd 49 Chapter 4.indd 49 6/28/2025 3:49:43 PM 6/28/2025 3:49:43 PM
Page 5
46
Curiosity — Textbook of Science for Grade 8
Electricity: Magnetic
and Heating Effects
4
z If we don’t have an electric lamp while making an electric circuit
with an electric cell, is there any other way through which we
can find out if current is flowing in the circuit?
z Is it possible to make temporary magnets? How can these
be made?
z We can generate heat by burning fossil fuels and wood; but how
is heat generated in various electrical appliances?
z How do we know if a cell or a battery is dead? Can all
cells and batteries be recharged?
z Share your questions
?
Probe and ponder
Chapter 4.indd 46 Chapter 4.indd 46 6/28/2025 3:49:31 PM 6/28/2025 3:49:31 PM
Chapter 4?—?Electricity: Magnetic and Heating Effects
47
It was the day of the science exhibition, and the school was
buzzing with energy. Mohini and Aakarsh, along with their
friends, went from one exhibit to another, eagerly exploring
different models, asking questions and taking notes. One simple
model really fascinated them. It was a working model of a lifting
electromagnet which was displayed by their senior, Sumana.
In it, instead of a hook like a typical crane, there was an iron
nail wrapped with a wire, which was connected to a battery.
When Sumana closed the circuit, the nail picked up iron paper
clips like a magnet. When she opened the circuit, the clips fell
off. Mohini and Aakarsh, were surprised. They remembered
learning earlier (in the chapter ‘Exploring Magnets’, Curiosity,
Grade 6) that magnetic materials were attracted by magnet and
that iron was a magnetic material. But in Sumana’s model, there
was no magnet, only an electric circuit. They were so excited that
they wanted to try it out themselves.
4.1 Does an Electric Current Have a Magnetic
Effect?
Activity 4.1: Let us investigate
z Collect a magnetic compass, an electric cell, a cell holder,
two drawing pins, a safety pin, two nails, two pieces of
connecting wires (one longer and one shorter), and two
small pieces of cardboard.
z Using two drawing pins, a safety pin, and a cardboard
piece, make a switch (as you made it earlier in the
chapter ‘Electricity: Circuits and their Components’ in
Curiosity, Grade 7).
z Place the cell in the cell holder.
z Fix two nails to a piece of cardboard as shown in
Fig. 4.1a. Fix the middle portion of the longer wire
stretched between the nails, such that it is slightly above
the surface of the cardboard. Attach one end of that
wire to the cell holder and another end to the switch.
z Connect the second wire between the cell holder and
the switch.
z Place the magnetic compass beneath the wire between
the two nails (Fig. 4.1a).
Fig. 4.1: An electric circuit
and a magnetic compass
(b)
(a)
Chapter 4.indd 47 Chapter 4.indd 47 6/28/2025 3:49:32 PM 6/28/2025 3:49:32 PM
48
Curiosity — Textbook of Science for Grade 8
While watching the compass needle, move the switch to
‘ON’ position to allow electric current to flow through the wire
(Fig. 4.1b). What do you observe?
z Now again while watching the compass needle, move the
switch to ‘OFF’ position. What do you observe this time?
z Move the switch between ‘ON’ and ‘OFF’ positions a few more
times. Carefully observe how the compass needle behaves
the each time.
You may have noticed that when the current flows, the compass
needle gets deflected from its original direction. When the current
stops, the needle returns to its original direction.
As we have learnt earlier (in the chapter ‘Exploring Magnets’
in Curiosity, Grade 6), the compass needle is a tiny magnet which
deflects when a magnet is brought near it and this magnetic effect
can act through any non-magnetic materials kept in between.
But why does the compass needle deflect when the current
flows through the wire? The deflection indicates that the current
carrying wire has a magnetic effect on the compass needle.
When the current stops, this magnetic effect disappears and
the compass needle returns to its original direction. The region
around a magnet or a current carrying wire where its magnetic
effect can be felt, such as by the deflection of a compass needle,
is said to have a magnetic field.
When electric current flows
through a conductor (like a wire), it
produces a magnetic field around it.
This phenomenon is known as the
magnetic effect of electric current.
The magnetic field disappears when
the current stops flowing.
Be a scientist
You have just now made the same discovery which
was made by the scientist Hans Christian Oersted
(1777–1851) in 1820, that is, the discovery that
electricity and magnetism are linked. He was a
professor at a university in Denmark. It is said that
once while giving a demonstration, he noticed that
whenever an electrical circuit was closed or
opened, the needle of a magnetic compass, lying
nearby, deflected. He investigated this and when he was certain that
an electric current indeed produced a magnetic field, he published
his findings. This led to other scientists repeating his experiment to
check if they got the same results, and further investigating the
connection between electricity and magnetism.
We have learnt about magnets
and electric current in earlier
grades. I used to think that there
was no link between the two. But
now we found that electricity
and magnetic effect are linked!
Chapter 4.indd 48 Chapter 4.indd 48 6/28/2025 3:49:38 PM 6/28/2025 3:49:38 PM
Chapter 4?—?Electricity: Magnetic and Heating Effects
49
The magnetic effect of electric current
has many practical applications, such as
in devices like electromagnets, electric
bells, motors, fans, loudspeakers,
and more.
4.1.1 Electromagnets
Activity 4.2: Let us explore
z Take around 50 cm long length of a flexible
insulated wire, an iron nail, an electric cell, and
few iron paper clips.
z Tightly wrap the wire around the nail in the form
of a coil, as shown in Fig. 4.2, and secure it with
an adhesive tape.
z Connect the ends of the wire to the cell. Take care
to not connect the wires to the cell for more than
a few seconds; otherwise, the cell may weaken
quickly.
z Bring the nail close to the iron paper clips and
lift up. Do the clips hang to the ends of the nail?
z Disconnect the wire from the cell to stop the
flow of electric current in the wire. Do the clips
fall down?
When electric current flows through the coil, the clips cling
to it. But when the current is stopped, the clips no longer cling
to it. Let us now try to investigate these observations in detail
through Activity 4.3.
Activity 4.3: Let us experiment
z Take around 100 cm long flexible insulated wire, a piece
of chart paper, an iron nail, an electric cell, two magnetic
compasses, and few iron/steel paper clips.
z Roll a piece of chart paper to make a cylinder of diameter
roughly equal to the width of a pencil. Secure it with an
adhesive tape.
z Tightly wind around 50 turns of the insulated wire on the
cylinder to form a cylindrical coil as shown in Fig. 4.3a.
Secure the wire with an adhesive tape.
Fig. 4.3: (a) A coil
of insulated wire
Can we use electric
current to make a
magnet?
Fig. 4.2: Coil of wire
connected with a cell
Chapter 4.indd 49 Chapter 4.indd 49 6/28/2025 3:49:43 PM 6/28/2025 3:49:43 PM
50
Curiosity — Textbook of Science for Grade 8
Fig. 4.3: (b) Coil and magnetic compasses;
(c) Coil connected to a cell; (d) Coil with
iron nail inserted; (e) Coil with iron nail
and clips
(d)
(e)
(c)
(b)
z Place the compasses near the two ends of the
cylindrical coil (Fig. 4.3b).
z Connect the two ends of the coil with the
terminals of the cell as shown in Fig. 4.3c and
observe the magnetic compasses. Do you find
any deflection in the needles of the compasses?
z Disconnect the wire from the cell. Do the needles
of the compasses come back to their original
positions?
z Insert an iron nail in the paper cylinder (Fig. 4.3d)
and repeat the steps. Is there any difference in
the deflection of the compass needles?
z Place some iron paper clips near the two ends
of the nail. Are the clips attracted to the ends of
the nail?
It is observed that when current is passed through
the cylindrical coil, it behaves like a magnet and
deflects the needle of a magnetic compass. When an
iron nail is inserted in the core of the coil, then the
coil becomes a stronger magnet and the deflection of
the magnetic compass needle is much more. It also
attracts iron clips (Fig. 4.3e). When the current is
stopped, the cylindrical coil loses its magnetic effect.
A current carrying coil that behaves as a magnet is
called an electromagnet. For practical applications,
most electromagnets have an iron core to make them
stronger.
Does electromagnet also have
two poles like a bar magnet?
Activity 4.4: Let us investigate
z Take the electromagnet made in Activity 4.3 and a magnetic
compass. Label the two ends of the coil as A and B.
z Place the magnetic compass near the end A of the coil as
shown in Fig. 4.4a.
z Connect the coil to the cell and observe the compass. Note down
which pole of the magnetic compass is attracted to end A.
Chapter 4.indd 50 Chapter 4.indd 50 6/28/2025 3:49:47 PM 6/28/2025 3:49:47 PM
Read More