GEN-PHYSICS-2-PPT-4

Welcome to Physics Class

  • Instructor: Teacher Monique I

Resistors in Series and Parallel

What is a Resistor?

  • An electrical component that limits or controls the flow of electrical current in a circuit.

  • Designed to have a specific resistance value, measured in ohms (Ω), which determines current flow impedance.

Functions of Resistors

  1. Control current flow through a circuit.

  2. Divide voltage in a circuit.

  3. Provide specific voltage drop to reduce electrical pressure.

  4. Limit current to protect components (acts as "current limiter").

  5. Create specific circuit conditions.

  6. Commonly used in electronic circuits.

Resistors in Series

Characteristics

  • When connected in series, total resistance (R_total) is the sum of individual resistances.

  • Formula: R_total = R1 + R2 + ... + Rn

  • Current through each resistor is the same.

  • Total voltage across resistors is the sum of individual voltages.

  • Equivalent resistance is always greater than any individual resistor.

Example Calculation

  • Given resistors:

    • R1 = 10 ohms

    • R2 = 20 ohms

    • R3 = 30 ohms

  • Connect in series with a 12-volt battery:

  • Calculation: R_total = R1 + R2 + R3 = 10 + 20 + 30 = 60 ohms.

Resistors in Parallel

Characteristics

  • When connected in parallel, the reciprocal of total resistance is the sum of the reciprocals of individual resistances.

  • Formula: 1/R_total = 1/R1 + 1/R2 + ... + 1/Rn

  • Voltage across each resistor is the same.

  • Total current is the sum of individual currents.

  • Equivalent resistance is always less than any individual resistor.

Example Calculation

  • Given resistors:

    • R1 = 20 ohms

    • R2 = 30 ohms

  • Connect in parallel with a 12-volt battery:

  • Calculation: 1/R_total = 1/20 + 1/30 = 0.08333 → R_total = 12 ohms.

Kirchhoff's Rules

Overview

  • Two fundamental principles used in circuit analysis to determine currents and voltages in electrical circuits.

  • Named after Gustav Kirchhoff, a German physicist.

  • Essential for understanding and analyzing complex circuits.

Kirchhoff's Current Law (KCL)

  • States that the algebraic sum of currents entering and exiting a junction (or node) is zero.

  • Total current flowing into a junction equals the total current flowing out.

  • Notes that a junction refers to a point where two or more circuit elements connect (resistors, capacitors, inductors).

R-C Circuits

Definition

  • Also known as resistor-capacitor circuits.

  • Contain both resistors and capacitors.

  • Commonly used in electronics for filtering, timing, and signal processing.

Applications

  • Timing circuits.

  • Smoothing and filtering of voltage waveforms.

  • Oscillators.

Magnetic Fields

  • Regions around a magnet or current-carrying conductor where magnetic forces are exerted on other magnets or moving charges.

  • Behavior described by laws of magnetism, particularly Maxwell's equations governing electromagnetism.

Types of Magnets

  1. Bar Magnet

  2. Horseshoe Magnet

  3. Two Bar Magnets

  4. Current-carrying Wire

  5. Toroid

  6. Solenoid

Parts of the Magnet

North Pole

  • Denoted by "N"; where magnetic field lines emerge.

South Pole

  • Denoted by "S"; where magnetic field lines enter.

Electromagnetism

  • A branch of physics dealing with interactions between electrically charged particles.

  • Describes how electric and magnetic fields are generated by charged particles and their interactions.

Lorentz Force

Definition

  • The force experienced by a charged particle moving through an electromagnetic field.

  • Named after physicist Hendrik Lorentz.

Formula

  • Lorentz Force Equation: F = - q (E + v x B)

    • F: Lorentz force (N)

    • q: charge of the particle (C)

    • E: electric field (V/m)

    • v: velocity of the particle (m/s)

    • B: magnetic field (Tesla or T)

Application

  • Basis for understanding phenomena such as the motion of electrons in magnetic fields, operation of electric motors/generators, and behavior of particles in accelerators.

Biot-Savart Law

Definition

  • Describes magnetic field generated by a current-carrying wire.

  • Named after physicists Jean-Baptiste Biot and Félix Savart.

Importance

  • Fundamental in magnetostatics.

  • Used to calculate the magnetic field from various current configurations (straight wires, loops, solenoids).

Ampère's Law

Overview

  • Formulated by physicist André-Marie Ampère.

  • Relates magnetic field around a closed loop to the electric current passing through that loop.