# CBSE 10th Science Exam 2021: Check Quick Revision Notes for Chapter 13 (Based on Revised Syllabus)

Gurmeet Kaur

Check quick revision notes for CBSE Class 10 Science Chapter 13 - Magnetic Effects of Electric Current. These notes have been prepared entirely according to the revised syllabus of CBSE Class 10 Science. Subject matter experts have prepared these notes to present all the topics (prescribed in the revised syllabus) in a clear and concise manner that are easy to understand and can be revised in a few minutes. These revision notes are best to prepare for the upcoming CBSE Class 10 Science Board Exam 2021.

Revision Notes for CBSE Class 10 Science Notes for Chapter 13 Magnetic Effects of Electric Current:

Magnetic field: The region surrounding a magnet, in which the force of the magnet can be detected, is named as magnetic field.

Magnetic field lines: The magnetic field lines can be explained as imaginary lines that graphically represent the magnetic field acting around a magnet.

Characteristics of magnetic field lines:

→ The field lines emerge from north pole and merge at the south pole

→ Inside the magnet, the direction of field lines is from its south pole to its north pole.

→ Thus the magnetic field lines are closed curves.

→ Magnetic field lines never intersect with each other.

Properties of magnetic field lines:

→ The tangent drawn to the magnetic field lines gives the direction of the magnetic field.

→ The closeness or density of the field lines is directly proportional to the strength of the field.

→ The field lines emerge from north pole and merge at the south pole.

→ Inside the magnet, the direction of field lines is from its south pole to its north pole.

→ Magnetic field lines form closed curves.

→ Magnetic field lines never intersect with each other.

Right-Hand Thumb Rule:

If a straight conductor is held in the right hand in such a way that the thumb points along the direction of the current then the fingers curl in the direction of magnetic field around it.

Field due to a current carrying conductor:

When current is passed through a straight current-carrying conductor, a magnetic field is produced around it.

The magnetic field lines are represented in the form of concentric circles around the conductor.

Magnetic field due to current through a circular loop:

→ Every point on the circular loop will act as a straight conductor.

→ Magnetic field lines are closer near the conductor which means the magnetic field is stronger near the periphery of the loop.

→ Magnetic field lines move away from each other as we move towards the centre of the current carrying loop.

→ At the centre, the magnetic field lines appear as straight lines.

Field due to a current carrying coil or solenoid

A coil of many circular turns of insulated copper wire wrapped closely in the shape of a cylinder is called a solenoid. When current is passed through it, it behaves similar to a bar magnet. One end of solenoid behaves as the north pole and another end behaves as the south pole.

The field lines inside the solenoid are in the form of parallel straight lines. This indicates that the field is uniform inside the solenoid.

Electromagnet:

→ Magnet formed by producing magnetic field inside a solenoid is called electromagnet.

→ It is temporary magnet that can be easily demagnetized by stopping the flow of electric current in the coil.

The strength of magnetic field due to a current carrying solenoid is proportional to:

→ the number of turns in the coil

→ magnitude of current flowing through the coil

Force on current carrying conductor:

→ When an electric conductor is placed in a magnetic field, it experiences a force.

→ The displacement in the conductor is the maximum when the direction of current is at right angle to the direction of magnetic field.

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. If the first finger points in the direction of magnetic field and the second finger in the direction of current, then the thumb will point in the direction of motion or the force acting on the conductor.

 Two main organs in the human body where the magnetic field produced is significant, are the heart and the brain. The magnetic field inside the body forms the basis of obtaining the images of different body parts through a technique called Magnetic Resonance Imaging (MRI). Analysis of these images helps in medical diagnosis.

Electric Motor: An electric motor is a rotating device that converts electrical energy to mechanical energy.

Principle of electric motor: An electric motor works on the principle that when a current carrying rectangular coil is placed perpendicular to the magnetic field it experiences a force which rotates it continuously.

Construction of electric motor:

→ It consists of a rectangular coil ABCD of insulated copper wire.

→ The coil is placed perpendicularly between the two poles of a magnetic field.

→ The ends of the coil are connected to the two halves P and Q of a split ring. Split rings act as a commutator which reverses the flow of current in the circuit.

→ The inner sides of split ring are attached to an axle which is free to rotate.

→ The external edges of the split ring touch two conducting stationary brushes X and Y.

→ These brushes are attached to the battery to complete the circuit.

Working of electric motor:

→ Current in the coil ABCD enters from the source battery through conducting brush X and flows back to the battery through brush Y.

→ Current flows through coil from A to B and then from C to D. The direction of magnetic field is from North to South.

→ By Fleming's left hand rule, the force acting on arm AB pushes it downwards while the force acting on arm CD pushes it upwards.

→ Thus the coil and the axle O rotate anti-clockwise.

→ After half rotation, Q touches brush X and P touches brush Y. Therefore the current in the coil gets reversed along the path DCBA.

→ Now, the current in CD flows from D to C and in AB from B to A.

→ So, CD moves downwards and AB moves upwards.

→ Thus, the coil and the axle keep rotating until the battery is switched off.

Commutator: A device that reverses the direction of flow of current through a circuit is called a commutator.

Significance of commutator: In electric motors, the split ring acts as a commutator. The split ring is used to reverse flow of current to make coil rotate in a single direction. Otherwise, in absence of split the coil would have rotated half in clockwise direction and half in anticlockwise direction.

The commercial motors use

(i) an electromagnet in place of permanent magnet

(ii) large number of turns of the conducting wire in the current carrying coil and

(iii) a soft iron core on which the coil is wound.

The soft iron core, on which the coil is wound, plus the coils, is called an armature. This enhances the power of the motor.

Electromagnetic induction: When a conductor (coil) is placed in a changing magnetic field, a potential difference is induced in it, which sets up an induced electric current in the circuit. This phenomenon is called electromagnetic induction.

The induced current is found to be the highest when the direction of motion of the coil is at right angles to the magnetic field.

Fleming’s Right Hand Rule: According to this rule, stretch the thumb, forefinger and middle finger of right hand so that they are perpendicular to each other. If the forefinger indicates the direction of the magnetic field and the thumb shows the direction of motion of conductor, then the middle finger will show the direction of induced current.

Topics deleted from the chapter:

 Electric Generator Direct current Alternating current: frequency of AC Advantage of AC over DC Domestic electric circuits
रोमांचक गेम्स खेलें और जीतें एक लाख रुपए तक कैश