NCERT Notes for Class 10 Science Chapter 13 Magnetic Effects of Electric Current
CBSE Class 10 Science notes will assist students in studying the topic thoroughly and clearly.
These CBSE Class 10 Science notes were written by subject experts who made the study material very basic, both in terms of language and format.
Magnetic field is the area around a magnet where its effect, i.e. its force, can be felt.
Magnetic field is a vector quantity.Tesla is the SI unit for magnetic field. Named after the American engineer Nikola Tesla, the smaller unit of magnetic field is Gauss.
Magnetic Field Lines
Magnetic field lines are imaginary lines that represent the magnetic field around a magnet.When iron filings are placed near a magnet, they form a pattern that resembles magnetic field lines.
The lines are drawn in the direction in which a compass needle’s magnetic North pole would migrate under the influence of a bar magnet’s field.
The field lines come from the North pole and unite at the South pole, according to convention.
Properties of Magnetic Field Lines
The properties of magnetic field lines are as follows:
(i) By convention, they begin at the North pole of a magnet and conclude at the South pole.
(ii) The curves on these lines are closed and continuous.
(iii) They cluster towards the poles, where the magnetic field is strong, and they are separated far from the poles, where the magnetic field is weak.
(iv) The field lines never cross each other. If they do, it means that the magnetic field at the point of junction has two directions, which is impossible.
Magnetic Field due to a Current-Carrying Conductor
A magnetic field is created around a conductor when electric current runs through it. The geometry of a current carrying conductor determines the pattern of
magnetic field it produces. Current carrying conductors of various forms produce various magnetic field patterns.
Magnetic Field due to a Current through a Straight Conductor
Magnetic field lines encircling a current-carrying straight conductor are concentric circles, with their centres on the wire.
At a given point, the magnitude of the magnetic field B produced by a straight current carrying wire is
(i) The current that I pass through the wire is proportional to the current that I pass through it.
B ∝ I ………(i)
The magnetic field produced becomes greater when the current is increased, and vice versa.
(ii)) Inversely proportional to the distance r from the wire
I.e. B ∝ 1/r …….(ii)
The magnetic field is stronger when it is closer to the conductor and weakens as it moves away from it.
By using Eqs. (i) and (ii), we get
B ∝ I/r
If the direction of current in a straight wire is known, Maxwell’s right hand thumb rule can be used to determine the direction of the magnetic field created by it.
Maxwell’s Right Hand Thumb Rule
It says that if you hold the current-carrying straight wire in your right hand so that the stretched thumb points in the direction of current, the direction of the magnetic field will be determined by the curl of the fingers. Maxwell’s corkscrew rule is another name for this rule.
Magnetic Field due to a Current through a Circular Loop
In the diagram, the magnetic field lines created by a circular coil may be seen.
The N magnetic field surrounds each point on a current-carrying circular loop in the shape of concentric circles. The rings would become larger and larger as we moved away from it.
The field looks to be a straight line when we reach the loop’s centre.
At a given position, the magnetic field produced by a current-carrying circular wire is-
(i) Directly proportional to the amount of current (I) flowing through it
I.e. B ∝ I ……(i)
(ii)Directly proportional to the number of turns (N) of the wire
I.e. B ∝ N …..(ii)
This is the case because the current in each turn is in the same direction. As a result, the field increases as a result of these turns.
As a result, the magnetic field strength produced by a current-carrying circular coil can be enhanced.
(a) increasing the number of turns of the coil.
(b) increasing the current flowing through the coil.
Magnetic Field due to Current in a Solenoid
A solenoid is a coil made up of many circular turns of insulated copper wire. To make a cylinder, these turns are tightly wrapped.
A current carrying a solenoid’s field lines are similar to those created by a bar magnet. This means that a current-carrying solenoid acts as if it has two poles: north and south.
The field lines inside the solenoid are parallel to each other. As a result, the magnetic field strength is constant throughout a solenoid.
When a piece of magnetic material, such as soft iron, is placed inside the coil, the strong magnetic field produced inside the solenoid can be used to magnetise it. The magnet that results from this process is known as an electromagnet. Only while the current is flowing through the solenoid does the magnetic effect last.
Electric bells, electric motors, telephone diaphragms, loudspeakers, and scrap metal sorting all require electromagnets.
Force on a Current-Carrying Conductor in a Magnetic Field
Except when placed parallel to the magnetic field, a current carrying conductor experiences a force when put in a magnetic field.The interaction between the magnetic field created by the current carrying conductor and the external magnetic field in which the conductor is located causes the force exerted on it in a magnetic field.
The force on the conductor is directed in one of two ways
(i) The current’s direction :Reversing the direction of current can change the direction of force on the conductor.
(ii) Magnetic field direction: Reversing the direction of the magnetic field by swapping pole positions can reverse the direction of force on the conductor.
The force on the conductor is greatest when the current direction is perpendicular to the magnetic field direction.
Fleming’s Left-Hand Rule
Fleming’s left hand rule determines the direction of force acting on a current carrying conductor in a magnetic field.
It states that if the forefinger, thumb, and middle finger of the left hand are all stretched perpendicular to each other, the forefinger points in the direction of the external magnetic field, the middle finger points in the direction of current, and the thumb points in the direction of force acting on the conductor.
It’s a revolving device that transforms electrical energy into mechanical energy.
It works on the theory that when a rectangular coil is placed in a magnetic field and current is delivered through it, two equal and opposite forces act on the coil, causing it to rotate constantly.
It is made out of a rectangular coil, ABCD, that is coupled to a current source and a switch.The commutators R1 and R2 are placed securely against the brushes X and Y and are fastened to the coil.
The commutator’s job is to reverse the direction of current flow through the coil every half cycle. Split rings are used as commutators in electric motors.
- Make sure the coil ABCD is horizontal. When the key is closed, current flows through brush X into the coil ABCD and back to the battery via brush Y via ring R2.
- Because the arms BC and AD are parallel to the magnetic field, no force acts on them. Arm AB is subjected to a downward force, whereas arm CD is subjected to an equivalent upward force. Fleming’s left hand rule is used to determine the direction of force. The coil rotates in an anti-clockwise direction as a result of this.
- The brushes lose contact with the rings when the coil spins vertically, and current stops flowing. However, due to inertia of motion, the coil does not come to a halt.
- The rings shift places and come into contact with opposite brushes as the coil revolves.
- The flow of current through the coil is reversed, but the direction of current on the right side of the coil stays unchanged.
- As a result, the force on the right-hand side is always upward, whereas the force on the left hand side is always downward.
- As a result, the coil continues to rotate counter-clockwise.
The motor’s rotational speed can be increased by
(i) increasing the current in the coil’s strength
(ii) ) increasing the area of the coil.
(iii) increasing the strength of the magnetic field.
Commercial Electric Motor
The following are the parts of a commercial electric motor:
(i) An electromagnet in the place of a permanent magnet.
(ii) The current carrying coil has a large number of turns of conducting wire.
(iii) The coil is coiled on a soft iron core. The term “armature” refers to the combination of a soft iron core and a coil. It boosts the motor’s performance.
Electric fans, refrigerators, mixers, washing machines, computers, MP3 players, and other appliances require electric motors.
An induced current is an electric current generated in a closed circuit by a changing magnetic field. Electromagnetic induction is the term for this phenomenon. Michael Faraday was the one who discovered it.
Fleming’s Right-Hand Rule
The galvanometer needle deflects as a bar magnet is moved towards a coil, indicating that an electric current is induced in the coil circuit. Fleming’s right hand rule determines the direction of an induced current.
It states that if the right hand’s forefinger, middle finger, and thumb are stretched at right angles to each other, with the forefinger pointing in the direction of the magnetic field and the thumb pointing in the direction of the wire motion, the induced current in the wire will flow in the middle finger’s direction.
It’s a device that can detect whether or not there’s current in a circuit. When there is no current flowing through the scale, the pointer remains at zero (the scale’s centre). The current deflects to the left or right of the zero point, depending on the direction of the current.
Ways to Induce Current in a Circuit
Inducing current in a circuit can be done in a variety of ways:
(i) A coil is moved in a magnetic field. A coil can be moved in a magnetic field or the magnetic field around it can be changed to generate current. In most cases, moving the coil in a magnetic field is more convenient. When you move a coil towards a magnet, it creates an electric current in the coil circuit, which shows up as a deflection in the galvanometer needle.
When the coil’s velocity is at a straight angle to the magnetic field, the induced current is found to be the highest. Reversing the direction of the magnetic field can change the direction of the induced current. There is no current induced in the coil if both the coil and the magnet are immobile.
(ii) By altering the magnetic field in the vicinity of a neighbouring coil
Consider two coils, one of which is the primary coil and the other is the secondary coil. A battery is linked to the primary coil.
The current in the primary coil takes a little time to rise from zero to maximum when the key (K) is closed. The magnetic field around this coil changes for a brief moment as a result of this.This causes a brief current to flow through the secondary coil. When the key (K) is opened, the same thing happens in the opposite direction. When the current in coil 1 is altered, current is induced in coil 2, as indicated by the deflection in the galvanometer needle.
Direct Current and Alternating Current
- Direct Current (DC)
Direct current is an electric current whose magnitude is either constant or changing but the direction remains constant. DC is the symbol for it. A voltaic cell, a dry cell, a battery, a DC ‘9 generator, and other DC sources exist.
- Alternating Current (AC)
Alternating current is an electric current whose magnitude varies over time and whose direction alternates on a regular basis. AC is the abbreviation for AC.
Hydroelectric generators, thermal power generators, and nuclear power generators are examples of AC sources. The frequency of AC is defined as the number of cycles performed by the AC in one second.
The frequency of AC in India is 50 Hz, which means that the direction of the conversation AC changes every 1/100 second.
The main distinction between AC and DC is that DC flows in one direction all of the time, whereas AC reverses direction on a regular basis. Electric power can be transmitted over great distances without much loss of energy, which is a benefit of AC versus DC.
It’s a machine that converts mechanical to electrical energy. The electromagnetic induction concept underpins the operation of an electric generator.
Parts of Electric Generator
The various components of an electric generator are described below:
(i) Armature It’s a coil with a lot of insulated copper wire twisted around a soft iron core.
(ii) Magnetism in the field It’s a strong magnet that creates a consistent magnetic field. Between the North and South poles, it is perpendicular to the axis of rotation of the coil.
(iii) Rings that slide Slip ring type commutators are utilised in AC generators. Slip rings are entire rings that come into contact with the coil’s ends. In contrast, a DC generator uses a split ring type commutator, which consists of half rings with which the armature coil’s ends are in touch.
(iv) Brushes If in contact with external devices and rings, there are two stationary metallic carbon brushes.
Types of Electric Generators
Electric generators are of two types:
- Alternating Current generator (AC generator)
- Direct Current generator (DC generator)
Alternating current (AC) is generated by it.
A rectangular armature coil (ABCD) is put in a high magnetic field to form an AC generator (between the two poles of a permanent magnet). The two slip rings (R1 and R2) keep the coil in contact with the load resistor through brushes (P and Q) without having to move the resistor.
The two rings linked to the coil also spin when the coil turns. When the coil starts rotating with arm AB going up and CD moving down (clockwise), the brushes Pand Q retain contact with the rotating rings (R1 and R2), severing the magnetic lines.
Current is induced in these arms in the direction of ABCD, according to Fleming’s right-hand rule. Arm CD moves up and arm AB moves down after half revolution.
As a result, the current direction in each segment shifts, resulting in net induced current in the DCBA direction. As a result, the polarity of current in each arm changes after every half rotation, resulting in an alternating current.
In a generator, the magnitude of the induced emf can be enhanced by
(i) increasing the number of turns of armature.
(ii)increasing the area of the armature.
(iii) increasing the armature’s rotational speed.
(iv)increasing the magnetic field’s strength.
It generates direct current (DC)
The construction of a DC generator/dynamo is similar to that of an AC generator, with the exception that split ring type commutators are employed in place of slip rings.
When using chis, one brush is always in contact with the arm travelling up in the field, while the other is in contact with the arm travelling down.
The direction of the induced current in the circuit is BADC when the coil starts spinning with arm AB moving down and CD moving up, according to Fleming’s right-hand rule. Ring R1 makes contact with brush B2 after half a circle, whereas ring R2 makes contact with brush B1.As a result, brush B2 is always in contact with the field wire travelling up, while the ocher is always in contact with the field wire moving down. As a result, the direction of current in the external circuit remains unchanged, resulting in a unidirectional current.
Domestic Electric Circuits
Two tiny copper or aluminium wires transport electricity generated from power plants to our houses. One is known as live wire (in red insulation cover), which has a potential of 220 V and a frequency of 50 Hz, and the other is known as neutral wire (in black insulation cover), which has no potential.
A main fuse connects these wires (live and neutral) to an electricity metre (attached in residences). They are connected to the home’s line wires via a main switch. In most houses, there are two different circuits: a lighting circuit with a 5 A fuse (bulbs, fans, etc.) and a power circuit with a 15 A fuse (power outlets, etc). (geysers, air coolers, erc.).
A separate fuse is provided for each distribution circuit. If one circuit experiences a fault, such as short circuiting, the accompanying fuse will blow, while the other circuit will be untouched. Parallel connections are made between various distribution circuits. Across the live and neutral wires, all electrical equipment such as lamps, fans, and sockets are linked in parallel.
Faults and Safety Measures in Domestic Electric Circuit
- Earth Wire
The metal body of appliances is earthed to prevent electrical shock. The appliance’s metal housing is connected to the earth (zero potential) by a metal wire known as earth wire (in green insulation cover). The metal wire has one end buried in the ground.
The top pin of a 3-pin plug is used to connect the appliances to the earth. Electrical shocks are avoided by earthing.
It is a precautionary measure. It is a thin wire formed of a tin-lead alloy with a low melting point of roughly 200 degrees Celsius. It is used to prevent overloading and short circuiting from causing harm.
Shore circuiting occurs when the live and neutral wires come into contact, either directly or through a conducting wire. In this situation, the circuit’s resistance is nearly zero, resulting in a huge current flow. This heats up the wire in a harmful way, potentially resulting in a fire.
When a significant number of high-power electrical appliances are turned on at the same time, the circuit is overloaded. Overloading is the term for this.
The huge quantity of current running through the wire heats up the wire excessively, perhaps causing a fire.