Electricity: Magnetic
and Heating Effects
4
Probe and ponder
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
46 ?
Curiosity — Textbook of Science for Grade 8
Reprint 2026-27
, 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).
(a)
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). (b)
Fig. 4.1: An electric circuit
and a magnetic compass
Reprint 2026-27
, 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
We have learnt about magnets through a conductor (like a wire), it
and electric current in earlier produces a magnetic field around it.
grades. I used to think that there
This phenomenon is known as the
was no link between the two. But
now we found that electricity
magnetic effect of electric current.
and magnetic effect are linked! 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.
48
Curiosity — Textbook of Science for Grade 8
Reprint 2026-27
and Heating Effects
4
Probe and ponder
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
46 ?
Curiosity — Textbook of Science for Grade 8
Reprint 2026-27
, 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).
(a)
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). (b)
Fig. 4.1: An electric circuit
and a magnetic compass
Reprint 2026-27
, 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
We have learnt about magnets through a conductor (like a wire), it
and electric current in earlier produces a magnetic field around it.
grades. I used to think that there
This phenomenon is known as the
was no link between the two. But
now we found that electricity
magnetic effect of electric current.
and magnetic effect are linked! 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.
48
Curiosity — Textbook of Science for Grade 8
Reprint 2026-27
