Magnetic Effects of Electric Current PDF

[Magnet]: Any substance that attracts iron or iron-like substances. - Every magnet has two poles i.e. North and South. - Like poles of magnets repel, while unlike poles attract each other. - A freely suspended bar magnet (or a suspended solenoid) aligns itself in nearly north-south dire...

[Magnet]: Any substance that attracts iron or iron-like substances. - Every magnet has two poles i.e. North and South. - Like poles of magnets repel, while unlike poles attract each other. - A freely suspended bar magnet (or a suspended solenoid) aligns itself in nearly north-south direction, with its north pole towards north direction. - Used in doorbells, magnetic compass, to separate iron fillings from other solid mixtures, MRIs, dynamos, generators, etc. [Magnetic Effects of Electric Current] - - - [Hans Christian Oersted:] a Danish physicist and chemist, he observed that a compass needle suffers a deflection when placed near a wire carrying an electric current. This discovery gave the first empirical evidence of a connection between electricity and magnetism. - On reversing polarity of battery (reversing the direction of current), the compass needle suffers a deflection opposite to the first case, revealing that magnetic field has direction. - His research later created technologies such as the radio, television and Fiber optics. The unit of magnetic field strength is named the oersted in his honor. [Compass Needle:] A compass needle is a small bar magnet that aligns with the Earth's magnetic field. - The end of the compass needle pointing north is called the north-seeking or north pole, while the end pointing south is the south-seeking or south pole. - The south pole of the needle points towards the north pole of the magnet. The north pole of the compass is directed away from the north pole of the magnet. [Magnetic Field (B):] When a bar magnet is placed near iron filings, the filings align in a specific pattern around the magnet. This pattern demonstrates the influence of the magnet in the space around it, showing the magnetic field. Its SI unit is Tesla (T). - - - [Magnetic Field Lines:] A field line is the path along which the north pole of a small magnetic compass moves when placed in a magnetic field. They are used to represent a magnetic field. - - - - - - - - - - [Magnetic Field Strength] - - - - - [Magnetic Field due to Current through a Straight Conductor] - - - - - - [Right-Hand Thumb Rule]: A method used to determine the direction of the magnetic field around a current-carrying conductor. - This rule is also known as Maxwell's Corkscrew Rule. - Imagine holding a current-carrying straight conductor in your right hand with your thumb pointing in the direction of the current. The fingers of your right hand will curl around the conductor in the direction of the magnetic field lines. This indicates the circular pattern of the magnetic field around a straight conductor. [Maxwell's Corkscrew Rule]: imagining a corkscrew moving in the direction of the current. As the corkscrew turns, the direction of its rotation represents the direction of the magnetic field. [Magnetic Field due to a Current through a Circular Loop] - When a straight current-carrying wire is bent into a circular loop, the magnetic field pattern around it changes. However, the direction of magnetic field inside the loop is same. - The magnetic field lines around a circular loop appear as concentric circles near each segment of the loop and become larger as the distance from the loop increases. - At the center of the circular loop, the arcs of these concentric circles from each segment of the loop appear as straight lines. - Each point on the loop generates a magnetic field that contributes to a uniform magnetic field at the center of the loop. - The magnetic field lines at the center point towards the same single direction due to the cumulative effect of each section of the loop. - For a circular coil with multiple turns (e.g., a coil with 'n' turns), the magnetic field strength increases. - The total magnetic field produced by a circular coil is 'n' times as large as that produced by a single turn because the field from each turn adds up in the same direction. - Magnetic field ∝ Current passing through the conductor - Magnetic field∝ 1/Distance from conductor - Magnetic field ∝ No. of turns in the coil - Magnetic field at its centre ∝ 1/radius of circular loop - Magnetic field is additive in nature i.e., magnetic field of one loop adds up to magnetic field of another loop. This is because the current in each circular turn has some direction. - By applying the Right-Hand Thumb Rule, we can confirm that all sections of the wire in the loop contribute to a magnetic field that points in the same direction within the loop. [Clock Face Rule]: A current-carrying circular wire (or loop) behaves like a thin disc magnet whose one face is a north pole and the other face is a south pole. The polarity of the two faces of a current-carrying circular coil (or loop) can be determined by using the clock face rule. - According to Clock face rule, look at one face of a circular wire (or coil) through which a current is passing: - if the current around the face of circular wire (or coil) flows in the Clockwise direction, then that face of the circular wire (or coil) will be South pole (S-pole). - if the current around the face of circular wire (or coil) flows in the Anticlockwise direction, then that face of circular wire (or coil) will be a North pole (N-pole). - If the direction of current in the front face of a circular wire is clockwise, then the direction of current in the back face of this circular wire will be anticlockwise (and vice versa). [Magnetic Field due to a Current in a Solenoid] [Solenoid]: A solenoid is a coil consisting of multiple turns of insulated copper wire wrapped closely in the shape of a cylinder. - When a current passes through the solenoid, the magnetic field lines and the magnetic field around it resemble those around a bar magnet. - This similarity means that: - One end of the solenoid behaves like a magnetic north pole. - The other end behaves like a magnetic south pole. - The magnetic field lines around the solenoid runs through the core and emerge from the north pole and merge at the south pole, following a closed-loop pattern similar to a bar magnet's field. - Inside the solenoid, the magnetic field lines are parallel and straight, indicating that the magnetic field is the same at all points inside the solenoid. (uniform field) - This uniform field means that the magnetic strength is consistent at all points within the solenoid. - Magnetic field inside a long solenoid decreases as we move towards ends of solenoid because magnetic field lines near the ends of solenoid start spreading out. - Magnetic field ∝ The number of turns in the solenoid. - Magnetic field ∝ The strength of current in the solenoid. - Magnetic field ∝ The nature of "core material" used in making solenoid. - The strong magnetic field produced inside a solenoid can be used to magnetize a piece of magnetic material, such as soft iron, by placing it inside the coil. - When magnetized, this setup is called an electromagnet. - if steel is used for making the core of an electromagnet, the steel does not lose all its magnetism when the current is stopped and it becomes a permanent magnet. [Electromagnet]: It consists of a core of soft iron wrapped around with a coil of insulated copper wire. It is a temporary magnet, so, can be easily demagnetised. Used in electric bells, or cranes. - Strength can be varied. - Polarity can be reversed. - Generally strong magnet. - the Strength of an Electromagnet ∝ The number of turns in the coil. - the Strength of an Electromagnet ∝ The current flowing in the coil. - the Strength of an Electromagnet ∝ 1/The length of air gap between its poles - An electromagnet is better than a permanent magnet because it can produce very strong magnetic fields and its strength can be controlled by varying the number of turns in its coil or by changing the current flowing through the coil. Also, its polarity can be reversed. [Permanent Magnet]: Cannot be easily demagnetised. Used in generator, loudspeaker. - Strength is fixed. - Polarity cannot be reversed. - Generally weak magnet. [Force on a Current-Carrying Conductor in a Magnetic Field] - When an electric current flows through a conductor, it generates a magnetic field around it. This magnetic field can exert a force on a nearby magnet. - The French scientist Andre Marie Ampere (1775--1836) suggested that if the magnetic field exerts a force on the current-carrying conductor, the conductor must also experience an equal and opposite force due to the magnet. [Demonstration of Force on a Conductor] - In an experimental setup, a current-carrying conductor (such as an aluminium rod) placed in a magnetic field experiences a force that causes it to move. - When the direction of the current in the conductor is reversed, the direction of the force on the conductor is also reversed. - By changing the direction of the magnetic field (e.g., by flipping the poles of a magnet), the direction of force on the current-carrying conductor changes as well. - This indicates that the direction of the force on the conductor depends on both the direction of the current and the direction of the magnetic field. - When current carrying conductor is placed perpendicular to the direction of magnetic field, the maximum displacement occurs indicating the maximum force on the conductor. i.e., Experiments have shown that the displacement of the rod is largest (or the magnitude of the force is the highest) when the direction of current is at right angles to the direction of the magnetic field. - This condition allows for the use of Fleming's Left-Hand Rule to determine the direction of the force on the conductor. [Fleming's Left-Hand Rule]: Stretch the thumb, forefinger, and middle finger of your left hand so that they are mutually perpendicular to each other. - The index finger points in the direction of the magnetic field. The middle finger points in the direction of the current. The thumb points in the direction of the force or motion acting on the conductor. - When a current-carrying conductor is placed in a magnetic field, the force exerted on it is perpendicular to both the direction of the current and the magnetic field. - Devices that rely on the interaction between current-carrying conductors and magnetic fields include: Electric Motors, Electric Generators, Loudspeakers and Microphones, and Measuring Instruments. [Magnetism in Medicine] - An electric current always produces a magnetic field. - In the human body, weak ion currents travel along nerve cells, producing tiny magnetic fields. For example, when we touch something, an electric impulse travels to the muscles, creating a temporary magnetic field. - These magnetic fields in the body are very weak---about one-billionth the strength of Earth\'s magnetic field. Despite this, these fields play an important role in specific organs. - The heart and brain are two main organs where the magnetic fields produced are significant. These fields can be detected, used for medical imaging & diagnostic purposes. [Magnetic Resonance Imaging]: MRI is a medical imaging technique that leverages the magnetic field inside the body to create detailed images of various body parts. - It works by detecting the body's natural magnetic fields & forming images based on these signals. - MRI images are analysed for medical diagnoses, helping in the detection and treatment of various conditions. [Domestic Electric Circuits] [Alternate Current (A. C.):] The current which reverses its direction periodically. - In India, A. C. reverses its direction in every 1/100 second. Time period = 1/100 + 1/100 = 1/50ss Frequency = 1/time period = 1/50 = 50Hz - AC can be transmitted over long distance without much loss of energy. - AC cannot be stored. - More dangerous as it produces more heat. [Direct Current (D. C.)]: The current which does not reverse its direction. - D. C. can be stored. - Loss of energy during transmission over long distance is high. - Sources of D. C.: Cell, Battery, Storage cells. [Live Wire]: This wire, usually covered in red insulation, is also called the positive wire. [Neutral Wire]: Covered in black insulation, this is referred to as the negative wire. - In India, the potential difference between the live and neutral wires is 220 V. [Earth Wire]: The earth wire is covered in green insulation and is connected to a metal plate buried deep in the ground near the house. - It acts as a safety measure by providing a low-resistance path for electric current, especially for appliances with metallic bodies (e.g., electric press, toaster, table fan, refrigerator). - This connection ensures that any leakage of current flows to the ground, keeping the appliance potential at earth level and reducing the risk of severe electric shock to users. [Electricity Distribution in the House] - Electric power is supplied to homes through a main supply (mains) that may come via overhead poles or underground cables. - At the meter board, the live and neutral wires connect to an electricity meter through a main fuse. The meter measures the amount of electricity consumed. - The main switch connects the meter to the internal house wiring, which distributes electricity to various circuits. - Domestic circuits typically have a parallel connection layout, allowing appliances to be independently connected across live and neutral wires. - Each appliance has a separate ON/OFF switch to control the current flow individually. - Appliances are connected in parallel to maintain the same potential difference across each device, ensuring consistent performance for each appliance. - A parallel arrangement allows each appliance to operate independently, without affecting others. - Pole ⇒ Main supply ⇒ Fuse ⇒ Electricity meter ⇒ Distribution box ⇒ To separate circuits [Electric Fuse]: The electric fuse is a critical safety component that prevents damage by interrupting current flow when overloading or short-circuiting occurs. - A fuse contains a thin wire that melts due to Joule heating when excessive current flows, effectively breaking the circuit and halting current flow. [Overloading]: It occurs when the current flowing through the circuit exceeds the safe capacity of the circuit's components, such as wires, outlets, or devices. This excessive current can generate too much heat, which poses risks like damaging appliances**,** causing fire, etc**.** - Overloading may occur when There is a Supply voltage increases accidentally, or too many appliances are connected to a single socket, causing an excessive current draw. [Short-Circuiting]: When live and neutral wires make direct contact, the resistance of the circuit becomes very small (they are in parallel). Hence, large current flows through the circuit, producing large amounts of heat and the circuit catches fire. - The fuse prevents potential damage by disconnecting the circuit in such cases. [Types of Circuits] - High-Power Appliances Circuit (15 A): This circuit is designed for appliances with higher power requirements, such as geysers and air coolers, and has a current rating of 15 A. - Low-Power Appliances Circuit (5 A): This circuit supplies electricity to lower power devices like bulbs and fans, with a current rating of 5 A. [Galvanometer]: It is an instrument used to detect the presence of current in a circuit. Also detects the direction of current. [Rectification]: The process of converting AC to DC. Examples of safety devices: MCB (miniature circuit breaker), fuse, earth wire