Magnetic Effects of Electric Current Class 10 Notes | Science |

Magnetic Effects of Electric Current Class 10 Notes | Science | 

Magnetic Effects of Electric Current Class 10 Notes : It was accidently discovered by Hans Christian Oersted that a compass needle got deflected when an electric current is passed through a metallic wire that is placed nearby. Oersted shows that electricity and magnetism are linked to each other and is commonly known as electromagnetism. 

Oersted is the SI Unit of magnetic field strength and that of magnetic field is Tesla. 

Magnetic Field

The region around a magnet wherein other magnet feels force of attraction or force of repulsion is known as magnetic field. It has both direction as well as magnitude. Its direction is taken to be the direction in which a north pole of the compass needle moves inside it. 

Magnetic Field Lines

The closed curve imaginary line that indicate the direction of the motion of north pole in magnetic field if magnet is free to do so. 

They emerge from north and merge into south pole whereas inside the magnet the direct of field lines are from south to north pole. They never intersect each other. 

Tangents drawn on these field lines at any point give the direction of magnetic field at that point. 

Relative strength of magnetic field can be determined by the closeness of the magnetic field.

Magnetic Field due to a Current Carrying Conductor

The direction of the magnetic field depends on the direction of current flow and get reversed on reversing the direction of current flow in the wire. The direction of deflection is generally remembered by SNOW rule.
According to this rule if the direction of the current flow is from South to north direction then the deflection of compass needle will be towards west and vice versa.

Magnetic field due to current through a Straight Conductor

The pattern of magnetic field line is directly dependent on the shape of conductor.

Factors affecting the magnetic field developed is due to the straight conductor-

Magnetic field is directly proportional to the amount of current flowing through the conductor
B ∝ I
Magnetic field strength is inversely proportional to the normal distance from the conductor
B ∝ 1 / r

Each point on the wire contributes to the magnetic field in the same direction.

Right Hand Thumb Rule

Imagine holding a current carrying straight conductor in your right hand in such a way that the thumb of the right hand will point along the direction of the current.
Then wrap the fingers of the hand around the conductor such that the direction of field lines of the magnetic field will be represented by the fingers.

In the case when field lines are perpendicular and directed in the plane of paper then it is represented by B ×

In the case where a magnetic field lines and are perpendicular and directed outside the plane of paper then it is generally represented by B •

Fleming’s left Hand Rule

States the thumb, forefinger and the central figure of your left and in such a way that they are mutually perpendicular to each other. Now your four finger will represent the direction of the magnetic field and the central finger will point towards the direction of current then direction of force acting on the conductor will be represented by thumb.

 

Magnetic field due to Current through a Circular Loop

It is considered that at every point of a current carrying circular loop, the concentric circles representing the magnetic field lines around it would become larger and larger as we move away from the wire.

At the centre of the circular loop all the magnetic field lines are in the same direction and ate at each other due to which the strength of magnetic field increases.

The magnitude of magnetic field produced by a circular current carrying circular loop depends on the following factors:
Strength of magnetic field is directly proportional to the current through the circular loop B ∝ I
Strength of magnetic field is inversely proportional to the radius of the circular loop B ∝ 1 / r

Magnetic Field due to a Solenoid

A long coil that is made up of large number of close turns of insulated copper wire is referred as solenoid.

The one end of solenoid will behave as north pole and the other end in will behave like South pole. If a current carrying solenoid is suspended freely then it will come to rest pointing towards the north direction.

The strength of magnetic field inside a long and straight current carrying solenoid is same at all the points.

The strength of the magnetic field produced by a current carrying solenoid depends on the following factors:

• The magnetic field strength is directly proportional to the number of turns in the solenoid
• It is directly proportional to strength of current in the solenoid.
• It also depends on the nature of core material that is used in making the solenoid. The soft iron rod as a core in the solenoid produces the strongest magnetism.

Force on Current Carrying Conductor in a Magnetic Field

Take a strong horseshoe magnet, its magnetic field lies in vertically upward direction and road a b lies between two poles of the magnet. North pole of the magnet should lie vertically below where is the South pole should lie vertically above the rod AB. It is observed that The road gets displaced towards the left.

If the direction of the current is reversed then direction of force will also get reversed. Also if the direction of magnetic field is reversed force is reversed.
Force is maximum when current and magnetic field are at right angle to each other.
F = BIL sin theta

Electric Motor

It is referred as a device that is used for conversion of electrical energy into mechanical energy.

It is based on the principle that when a rectangular coil is placed in a magnetic field and current is passed through it then a force will act on the coil which rotate it continuously.

It finds its applications in fans, refrigerators, mixers, washing machines, computer, MP3 players.

Construction: It basically consists of a rectangular coil ABCD insulated copper wire. It is placed between the two poles of the horseshoe magnet. The end of the coils are connected to two halves P and Q of split ring commutator.
External conducting edges touch stationary metal brushes X and Y.

Working:
The force acting on arm AB will push it downward whereas the force acting on arm CD will push it upward. Hand coil and axle rotates anticlockwise.
Commutator- It is the device that reverses the direction of the flow of current within a circuit. In motor, it is split ring commutator.
Armature- The soft iron core on which the coil is wounded plus the coils are called armature. It efficiently enhances is the power of the motor.
Brushes (X and Y)- It is a device that conducts current between the stationary wires and the moving parts.

Modifications in commercial motors

• An electromagnet is placed in place of permanent magnet.
• Large number of turns of conducting wire in current carrying coil.
• A soft iron core on which coil is found.

Electromagnetic Induction

The phenomenon of setting up of an electric current or an induced EMF by changing the magnetic lines of force by a moving conductor is commonly referred as electromagnetic induction.

English physicist Michael Faraday discover that how can a moving magnet be used in order to generate the electric current.

Faraday Experiment 1

Generation of electric current due to the moving magnet
If a strong bar magnet is allowed to move quickly towards or away from the one end of the coil. Then galvanometer will show deflection and this deflection becomes zero when the magnet stops. Similarly when the bar magnet is at fixed position then move the coil towards the magnet and momentary deflection is observed in galvanometer.

Induced current depends on the following three factors:

• Strength of magnet
• Number of turns in the coil
• Speed of movement of the magnet

Faraday Experiment 2

Generation of electric current in a coil due to change in current in the neighbouring coil
The coil that is connected to the battery is called primary coil and the coil that is connected to the galvanometer is referred as secondary coil.

If the key is closed in the first coil then current is induced in the second coil for moments. Similarly if the key is open then current want flow and again a current will be induced in coil 2 for moments.
Thus, current is induced due to potential difference.

Fleming’s Right Hand Rule

Stretch the thumb, forefinger and Central finger of your right hand in such a way that they are mutually perpendicular to each other. If four finger indicates the direction of the magnetic field and thumb points towards the direction of the motion of conductor when the central figure will show the direction of the induced current in the conductor.

Magnetic Effects of Electric Current Class 10 Notes & Questions

Question: Rahul draws magnetic field lines that are close to the axis of a current carrying circular loop. As the distance between Rahul and the centre of circular loop increases, he observes that the lines keep on diverging. Explain the reason for his observation.

Answer: The pattern of the magnetic field lines due to a current carrying circular loop are circular near the current carrying loop due to the reason that the concentric circle representing the magnetic field lines become bigger and bigger. The magnetic field lines are considered straight at the centre of the loop. Hence, on moving away from the centre of the circular loop the magnetic field lines keep on diverging.

Question: State suitable reason that why two magnetic field lines never intersect each other?

Answer: Two magnetic field lines never intersect each other since if they intersect each other then there will be to direction of magnetic field at any point which is not possible. 

Question: Explain how does the strength of the magnetic field produced due to a current carrying conductor changes
(a) With the change in distance from the conductor?
(b) With an increase in current flowing in the conductor?

Answer: (a) The strength of the magnetic field produced due to a current carrying wire at any point is inversely proportional to the distance of that point from the wire.
(b) Strength of the magnetic field is directly proportional to the current flowing in the conductor.s

Question:(a) A coil of an insulated wire is connected to a galvanometer. What would be observed if a bar magnet with its south pole towards one face of the coil is
(i) Moved quickly towards it
(ii) Move quickly away from it
(iii) Place to near its one and
(b) Identify the phenomena involved in above activities.
(c) Name the rule which can be used to determine the direction of current in each case.

Answer: (a) (i) If the magnet with its is moved quickly towards it the galvanometer will deflect towards left.
(ii) If the magnet is moved quickly away from it the galvanometer will be deflected towards right.
(iii) If it is placed near its one face then the deflection in the galvanometer will be zero.
(b) The phenomenon involved in the above activities is Electromagnetic Induction.
(c) The direction of the induced current will be determined by Fleming’s Right Hand Rule.

Question: What is the work of split rings in an electric motor?

Answer: It is also known as commutator and is basically used in order to reverse the direction of current flowing through the motor coil after every half rotation of the coil. Does the direction of the force remain unchanged on two sides of the coil resulting in continuous rotation of the coil in same direction. 

 

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