Magnetic Effects of Electric Current 10th Physics

Minerva Sr. Sec. School Gh
6/13/2021 11:24:11 AM MINERVA SR. SEC. SCHOOL GHUMARWIN 1
10th
Physics

Magnet
A substance which attracts small pieces of metals like iron,
nickel and cobalt is called a magnet.
Or
A substance which attracts small pieces of iron and
points in North-South direction when suspended
freely is known as magnet.

Natural Magnet
Natural magnets are irregular in shape.
Moreover they are weak magnets.
Magnetite is a naturally occurring iron ore.
This iron ore is an iron oxide whose chemical
formula is Fe3O4.
This natural magnet of dark blackish brown
color is also known as black stone or lodestone
 or leading stone or kissing stone.

Artificial Magnets
An iron bar can be made a magnet by rubbing it with a
natural magnet. Such a magnet is known as man made
magnets or artificial magnet.
Artificial magnets are of different shapes.
E.g. A bar magnet (i.e. rectangular in shape)
and U shaped magnets etc.

Poles of a Magnet
There are two poles of a magnet.
1. North Pole 2. South Pole
Note:
The end of the magnet which points towards the north of earth
is called a north seeking pole or north pole of the magnet.
And the end of the magnet which points towards the south of earth
is called a south seeking pole or south pole of the magnet.

Basic Properties of a Magnet
1.A magnet has two poles: north pole and
south pole.
2.Magnetic poles always exist in pairs.
3. Like poles repel each other and unlike
poles attract each other.

4. Poles of a magnet are of equal strength.
5. When a magnet is suspended freely with the
help of a light thread then it always aligns
along the north-south direction. This is called
the directive property of magnet.
6. Every magnet attracts small pieces of iron,
nickel, cobalt etc. towards itself.
Basic Properties of a Magnet (to be cont.

Relation b/w Magnetism & Electricity
 Electric charges are of two types- Positive and
Negative.
Magnetic poles are of two types- North pole
and South pole.
 Like charges repel each other.
Like poles of magnet repel each other
 Opposite charges attract each other

Relation b/w Magnetism & Electricity
Charged objects set up electric field
around themselves
Magnetic objects set up magnetic
field around themselves.
Certain substances can be charged
by rubbing.
Certain substances can be
magnetized by rubbing

Oersted’s Discovery
When electric current flows
through a current carrying
conductor, it produces a
magnetic field around it.
This can be seen with the help
of a magnetic needle which
shows deflection.
The more the current, the
higher the deflection. If the
direction of current is reversed,
the direction of deflection is

In the nutshell, Oersted’s experiment demonstrated
and concluded that “around every current carrying
conductor, there exists a magnetic field”.

Magnetic Field
The region around a magnet where the force of attraction or
repulsion can be detected is called magnetic field.
Or
The region around a magnet or a current carrying
conductor in which its magnetic force can be detected is
said to be its magnetic field.
1. It is denoted by B
2. It is a vector quantity.
3. Magnetic field around a magnet can be detected by using

Magnetic Field Lines
The imaginary lines (curves) which are used to represent
magnetic field.
Or
Magnetic field line is also defined as the path followed by a
single north pole in a magnetic field if it is free to do so.
1. We can see the pattern of magnetic field lines around a
bar magnet using
iron fillings. For this, place a bar magnet
on a card board, sprinkle some iron fillings
around the magnet and tap the card board

Properties of Magnetic Field Lines
1. Outside a magnet, magnetic field lines are directed from
north pole to south pole.
2. Inside a magnet, magnetic field lines are directed from
south pole to north pole.
3. Magnetic field lines are closed and continuous curves.
4. The magnetic field lines are closer at the poles, which
means strength of magnetic field is large at the poles and
weak at the center.

Properties of Magnetic Field Lines
5. The direction of magnetic field at a point on the magnetic
field line is given by drawing a tangent at that point.
6. Two magnetic field lines never intersect each other.
Because if they do so, then at the point of intersection two
tangents can be drawn, which means two directions of the
magnetic field at a single point which is not possible.

Types of Magnetic Field
Uniform Magnetic Field
• Magnetic field in a given space is said to be uniform if its
magnitude and direction at every point remains same.
• Uniform magnetic field is represented by equidistant parallel
straight lines and equal distances between parallel lines.
Non-Uniform Magnetic Field
• Magnetic field in a given space is said to be non-uniform if its
magnitude or direction or both are not same at every point in
the space.

Types of Magnetic Field

M. F. due to straight current carrying conductor
When an electric current is passed through a straight
conductor, magnetic field is set up around the conductor
which can be felt using iron fillings or a magnetic needle.

M. F. due to straight current carrying conductor
So, we have seen that the iron fillings are arranged in the
form of concentric circles around the current carrying
conductor with their centres lying on the conductor.

Direction of Magnetic Field Lines
Direction of magnetic field lines around the current carrying
straight conductor is given by a rule known as “RIGHT
HAND THUMB RULE”.
RIGHT HAND THUMB RULE: It states that ‘If a
current carrying conductor is held in the right
hand such that the thumb points in the direction
of current, then the fingers wrapped around
the conductor shows the direction of the
magnetic field’.

Direction of Magnetic Field Lines (cont..)

Factors on which the magnitude of M.F. depends
It has been observed experimentally that the magnitude of
magnetic field (B) depends on the following factors:
1. Magnitude of electric current (I)
Strength of magnetic field due to straight current carrying
conductor is directly proportional to the strength of electric
current (I) passing through the conductor. B
∝ I
It means, strength of magnetic field increases on increasing
the electric current and vice-versa.
2. Distance from the conductor (r)
Magnitude of mag. field is inversely proportional to the
distance of a point from the current carrying conductor.

It means, magnetic field at a point decreases on increasing
the distance of point (r) from the current carrying
conductor.
 Unit of Magnetic Field
Tesla (T) is the SI unit of magnetic field and the CGS unit of
magnetic field is Gauss (G). It is a smaller unit than Tesla.
 1 T = 104 G

M. F. due to Current Carrying Circular Coil
 Ampere found that the loop of wire also
had a magnetic field.
 Magnetic field lines near the boundary
of
circular coil are approximately circular and
concentric. This is because a small part of
coil can
be considered as a straight conductor.
 Near the centre of coil, field lines are
nearly straight lines. It means, magnetic
field at the
centre of coil is nearly uniform.
 Strength of magnetic field is maximum
at the centre

Direction of Magnetic Field Lines (cont..)
Direction of magnetic field line across the coil is given by
right hand thumb rule.
But, to identify that current carrying coil behaves like a
magnet (poles) or not, clock face rule is used.

The magnitude of magnetic field at the centre of the coil
depends on the following factors:
1. Magnitude of Current: Strength of magnetic field at the
centre of coil depends directly on the strength of electric
current (I) passing through the coil.
B ∝ I
2. Radius of the coil (r): Strength of magnetic field at the
centre of coil is inversely proportional to the radius of the
coil.
B ∝ 1/r
3. Number of turns in the coil (N): Strength of magnetic field
is directly proportional to the total number of turns in the

M. F. due to Current Carrying Solenoid
Solenoid: An insulated copper wire of many circular turns
wrapped closely in the form of a spring or helix having its
length greater than the diameter of its turns is called a
solenoid. It is used to generate uniform magnetic field.

M. F. due to Current Carrying Solenoid (contd..)
If we look at solenoid from end A, we observe that current
flows in clockwise direction, which means end A is acting
like a South pole.
The current in end B appears to flow in anticlockwise
direction which means end B acting like a north pole.
Thus current carrying solenoid behaves as a
magnet.
As we know that magnetic field lines
outside a magnet move from North pole to
south pole, hence, the direction of magnetic
field lines are shown in fig.

M. F. due to Current Carrying Solenoid (contd..)
We see that the magnetic field lines inside the solenoid are
nearly straight lines. Thus, the magnetic field lines inside a
solenoid is uniform. This pattern of magnetic field lines is
identical to the pattern of magnetic field lines due to a bar
magnet.
Hence, a current carrying solenoid behaves as a bar
magnet.

1. Magnitude of Current: Strength of magnetic field is
directly proportional to the magnitude of electric current (I)
passing through the solenoid.
B ∝ I
2. Number of turns per unit length of solenoid (n = N/L):
Strength of magnetic field is directly proportional to the
number of turns per unit length of the solenoid.
B ∝ n
 It means, closely packed solenoid will have stronger
magnetic field as compared to loosely packed solenoid of
same length and current.

Electromagnet & Permanent Magnet
Electromagnet:
When soft iron is inserted into the solenoid carrying
current, it becomes a magnet. Such a magnet is called
electromagnet.

Electromagnet & Permanent Magnet
 The iron inserted inside the solenoid is called core.
 Electromagnet possesses magnetic nature as long as
current flows through it.
 Hence, electromagnet is a temporary magnet formed by
inserting iron inside a current carrying solenoid.
 Soft iron is used because of its property that it
immediately loses magnetic properties as the current is
switched OFF.
 Strength of magnetic field of electromagnet can be
changed by changing the strength of current passing
through the solenoid. If the direction of current is
reversed in solenoid, then the polarity of electromagnet

Permanent Magnet
 When a steel bar is placed inside a solenoid and current
is passed through it, the steel bar gets magnetized
permanently.
 It is removed from the solenoid and can be used as a
strong magnet.
 Unlike electromagnet, no current is required for its
working as a magnet.
 Steel is used to make permanent magnet because steel
does not loose its magnetic properties on switching OFF
the current..
 Permanent magnets are usually weaker than

Force on a current carrying conductor placed in
a magnetic field
Ampere suggested that if a current carrying conductor
produces a magnetic field and exerts a force on a magnet,
then a magnet should also exerts a force on a current
carrying conductor.
Experimentally, this has been found true.
Magnetic field produced by a magnet, exerts a force on a
current carrying conductor and produces motion in it.
This can be demonstrated through the Kicking Wire
Experiment.

Kicking Wire Experiment
If an aluminium rod is suspended
horizontally by a wire between the
poles of a horse shoe magnet and
current is passed through the wire,
then the aluminium rod feels force
on it and gets displaced. If the
direction of current is reversed, then
also aluminium rod feels force on it
and this time direction of
displacement also reversed.
The force exerted is maximum if the

The direction of force experienced by a current carrying
conductor placed in an external magnetic field is given by
Fleming’s left hand rule.
Fleming’s Left Hand Rule

Fleming’s Left Hand Rule
According to this rule, “stretch the thumb, forefinger and
middle finger of your left hand such that they are mutually
perpendicular to one another.
If forefinger points in the direction of magnetic field, middle
finger points in the direction of current then thumb will
point in the direction of motion or in the direction of force
acting on the conductor, as shown in figure.

Magnetic Effects of Electric Current 10th Physics

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