Unit 1 Electricity and Capacitance PDF

Charge, Current, Voltage, Resistance, and Ohm's Law 1. Charge (Q): o Definition: Electric charge is a fundamental property of matter that causes it to experience a force when placed in an electric and magnetic field. It is measured in coulombs (C). o T...

Charge, Current, Voltage, Resistance, and Ohm's Law 1. Charge (Q): o Definition: Electric charge is a fundamental property of matter that causes it to experience a force when placed in an electric and magnetic field. It is measured in coulombs (C). o Types: There are two types of charges: positive and negative. Like charges repel, while opposite charges attract. o Quantization: Charge is quantized, meaning it exists in discrete amounts, typically in multiples of the elementary charge (e), where e=1.6×10−19 e = 1.6 \times 10-19 e=1.6×10−19 C. 2. Current (I): o Definition: Electric current is the rate of flow of electric charge through a conductor. It is measured in amperes (A). o Formula: I=Q/t, where Q is the charge and t is time.  o Direction: Conventional current flows from the positive terminal to the negative terminal of a power source, although the actual flow of electrons is in the opposite direction. 3. Voltage (V): o Definition: Voltage, or electric potential difference, is the work done to move a unit charge from one point to another. It is measured in volts (V). o Formula: V=W/Q , where W is the work done, and Q is the charge. o Role: Voltage is the driving force that pushes current through a circuit. 4. Resistance (R): o Definition: Resistance is the opposition that a material offers to the flow of electric current. It is measured in ohms (Ω). o Factors Affecting Resistance: Resistance depends on the material, length, cross-sectional area of the conductor, and temperature.  o Formula: R=ρL/A , where ρ is the resistivity of the material, L is the length, and A is the cross-sectional area. 5. Ohm's Law: o Statement: Ohm's Law states that the current flowing through a conductor between two points is directly proportional to the voltage across the two points, provided the temperature remains constant. o Mathematical Expression: V=IR where V is the voltage, I is the current, and R is the resistance. o Application: Ohm's Law is fundamental in analysing electrical circuits, allowing for the calculation of voltage, current, or resistance when the other two quantities are known. Magnetic Effects of Current and Solenoids Electric currents generate magnetic fields, a phenomenon crucially demonstrated by solenoids, which are coils of wire often wound around a cylindrical core. Key points include: 1. Magnetic Field Generation: When electric current flows through a conductor, it creates a magnetic field around the conductor according to the right-hand rule, where the thumb points in the direction of the current and fingers curl in the direction of the magnetic field. 2. Solenoids: A solenoid is a coil of wire wound in the form of a helix. When current flows through a solenoid, it produces a strong magnetic field inside the coil and a weaker one outside, resembling the field pattern of a bar magnet. 3. Applications: Solenoids find extensive use in electromechanical devices such as electromagnetic relays, actuators, and inductor cores. They can create controlled magnetic fields used in applications ranging from medical devices to industrial machinery. What is a Capacitor? A capacitor is a passive electronic component that stores electrical energy in an electric field. It consists of two conductive plates separated by an insulating material known as a dielectric. Capacitors are widely used in electronic circuits for a variety of purposes, including filtering, energy storage, and signal processing. Principle of Operation The basic principle behind a capacitor is the ability to store and release electrical energy. When a voltage is applied across the plates of a capacitor, an electric field is established across the dielectric. This causes positive charge to accumulate on one plate and an equal but opposite negative charge on the other plate. Charge Stored in a Capacitor The amount of charge Q stored in a capacitor is directly proportional to the voltage V applied across its plates and is given by the formula: Q=C× V Where: Q is the charge stored in coulombs (C). C is the capacitance of the capacitor in farads (F). V is the voltage across the capacitor in volts (V). Capacitance Capacitance C is a measure of a capacitor's ability to store charge per unit voltage and is determined by the physical characteristics of the capacitor: C=ϵ0⋅ϵr⋅A/d Where: ϵ0 is the permittivity of free space (8.854×10−12 F/m) ϵr is the relative permittivity (dielectric constant) of the material between the plates.  A is the area of the plates in square meters. d is the distance between the plates in meters. Energy Stored in a Capacitor The energy E stored in a charged capacitor is given by: This energy is stored in the electric field between the plates and can be released when the capacitor is connected to a circuit. Applications of Capacitors Capacitors are essential in various applications, including: Filtering: In power supplies, capacitors smooth out fluctuations in voltage. Timing Circuits: Capacitors are used in conjunction with resistors to create time delays in circuits. Energy Storage: Capacitors store energy that can be released quickly, useful in camera flashes and other high-power applications. Signal Processing: Capacitors block direct current (DC) while allowing alternating current (AC) to pass, making them vital in signal coupling and decoupling.