Grade 11
  1. Mechanics  1.1. dynamics  1.1.1. Motion in one dimension  1.1.2. Motion in two and three dimensions  1.1.3. Displacement and Distance  1.1.4. Speed and Velocity  1.1.5. Acceleration and deceleration  1.1.6. Graphical analysis of motion  1.1.7. Equations of motion (advanced derivations)  1.1.8. Free fall and terminal velocity  1.1.9. Projectile motion  1.1.10. Relative velocity in one and two dimensions  1.1.11. Motion of a car on an inclined plane  1.2. Dynamics  1.2.1. Newton's laws of motion and their applications  1.2.2. Inertia and Newton's first law  1.2.3. Force and types of force  1.2.4. Static and kinetic friction  1.2.5. Circular motion and centripetal acceleration  1.2.6. Non-uniform circular motion  1.2.7. Banking of roads and curves  1.2.8. Momentum and Impulse  1.2.9. Conservation of momentum in one and two dimensions  1.2.10. Applications of Newton's Third Law  1.3. Work, Energy and Power  1.3.1. Work done by a constant and variable force  1.3.2. Work–energy theorem  1.3.3. Kinetic and potential energy  1.3.4. Gravitational and elastic potential energy  1.3.5. Conservation of mechanical energy  1.3.6. Power and instantaneous power  1.3.7. Efficiency of machines  1.3.8. Work done by conservative and non-conservative forces  1.4. Rotational motion  1.4.1. Torque and angular acceleration  1.4.2. Rotational equilibrium  1.4.3. Moment of inertia and its applications  1.4.4. Angular momentum and its conservation  1.4.5. Kinetic energy of rolling motion and rotation  1.4.6. Parallel and Perpendicular Axis Theorem  1.4.7. Dynamics of rotational motion
  2. Gravitational force  2.1. Universal gravitation  2.1.1. Newton's law of universal gravitation  2.1.2. Gravitational field and potential  2.1.3. Change in acceleration due to gravity  2.1.4. Kepler's laws of planetary motion  2.1.5. Orbital mechanics and satellites  2.1.6. Escape velocity and orbital velocity  2.1.7. Weightlessness and free fall  2.1.8. Gravitational potential energy and energy in orbits  2.1.9. Black holes and gravitational lensing
  3. Properties of matter  3.1. Fluid mechanics  3.1.1. Density and pressure in liquids  3.1.2. Pascal's theory and applications  3.1.3. Archimedes' Principle and Buoyancy  3.1.4. Bernoulli's equation and applications  3.1.5. Continuity equation and the Venturi effect  3.1.6. Surface tension and capillarity  3.1.7. Viscosity and Poiseuille's Law  3.1.8. Reynolds number and turbulence  3.2. Elasticity and deformation  3.2.1. Hooke's law and the stress-strain relation  3.2.2. Elastic modulus and applications  3.2.3. Deformation and yield strength of solids
  4. Thermal physics  4.1. Heat and temperature  4.1.1. Thermometric properties and temperature scale  4.1.2. Thermal expansion of solids, liquids and gases  4.1.3. Heat transfer system  4.1.4. Specific heat capacity and calorimetry  4.1.5. Latent heat and phase change  4.2. Kinetic theory of gases  4.2.1. Molecular model of gases  4.2.2. Kinetic explanation of temperature  4.2.3. Ideal Gas Equation and Deviations  4.2.4. Mean free path and Maxwell–Boltzmann distribution  4.3. Laws of Thermodynamics  4.3.1. Zeroth Law and Thermal Equilibrium  4.3.2. First Law and Internal Energy  4.3.3. The Second Law and Entropy  4.3.4. Carnot cycle and heat engines  4.3.5. Refrigerators and heat pumps
  5. Waves and oscillations  5.1. Simple Harmonic Motion  5.1.1. Equations of SHM  5.1.2. Energy in SHM  5.1.3. Damped and forced oscillations  5.1.4. Resonance and applications  5.1.5. Pendulum and spring-mass system  5.2. Wave motion  5.2.1. Types of mechanical waves  5.2.2. Wave motion and energy transport  5.2.3. Superposition Principle and Standing Waves  5.2.4. Reflection, Refraction and Diffraction  5.2.5. Doppler effect in sound and light  5.2.6. Pulsations and interference
  6. Electricity and Magnetism  6.1. Electrostatics  6.1.1. Electric charge and conservation  6.1.2. Coulomb's law and its applications  6.1.3. Electric field and electric flux  6.1.4. Electric potential and potential energy  6.1.5. Capacitance and Energy Stored in a Capacitor  6.2. Current Electricity  6.2.1. Ohm's law and electrical resistance  6.2.2. Resistivity and temperature dependence  6.2.3. Kirchhoff's Laws and Circuit Analysis  6.2.4. Electrical power and efficiency  6.2.5. Combination of resistors  6.3. Magnetism and Electromagnetism  6.3.1. Magnetic fields and their sources  6.3.2. Magnetic force on moving charges  6.3.3. Electromagnetic induction  6.3.4. Faraday's and Lenz's laws  6.3.5. Inductance and Transformer  6.3.6. Alternating current and its applications
  7. Optics  7.1. Reflection and Refraction  7.1.1. laws of reflection and refraction  7.1.2. Mirrors and lenses  7.1.3. Total internal reflection and optical fiber  7.2. Wave optics  7.2.1. Interference and Diffraction  7.2.2. Young's double-slit experiment  7.2.3. Polarization of light
  8. Modern Physics  8.1.1. Photoelectric effect and Einstein's theory  8.1.2. Wave–particle duality  8.1.3. Heisenberg's uncertainty principle  8.1.4. Compton Effect  8.2. Atomic and Nuclear Physics  8.2.1. Atomic model and energy levels  8.2.2. Radioactive decay and half-life  8.2.3. Nuclear Fission and Fusion
  9. Electronics and Communication  9.1. Semiconductors  9.1.1. pn junction and diode  9.1.2. Transistors and Logic Gates  9.1.3. Integrated Circuits and Applications  9.2. Communication Systems  9.2.1. Basics of Analog and Digital Communication  9.2.2. Wireless and Optical Communication  9.2.3. Modulation and Demodulation

Grade 11 → Electricity and Magnetism → Current Electricity ↓


Ohm's law and electrical resistance


Understanding electricity is an essential part of physics, and two fundamental concepts in this field are Ohm's law and electrical resistance. These concepts allow us to understand how electrical currents behave in components such as conductive materials, resistors, wires, and circuits.

What is Ohm's law?

Ohm's law is a basic principle in electronics and electrical engineering that relates the electric current flowing through a conductor to the voltage across it and its resistance. It can be easily expressed using the formula:

V = I * R

Where:

  • V is the voltage on the conductor in volts (V)
  • I is the current flowing through the conductor in amperes (A)
  • R is the electrical resistance offered by the conductor in ohms (Ω)

Understanding the concepts

Voltage (V)

Voltage is the electric potential difference between two points in a circuit. It is the driving force that pushes electric current through a conductor. The more voltage we have, the more potential energy is available to move electrons through the conductor.

Current (I)

Current is the rate at which electric charge passes through a point in a circuit. It is measured in amperes. An ammeter is an instrument commonly used to measure current in a circuit. The flow of current can be compared to water flowing through a pipe. The larger the pipe (or wire), the easier it is for water (or electrons) to pass through it.

Resistance (R)

Resistance is a measurement of how much a substance or object resists the flow of electric current. It is measured in ohms (Ω). In the context of our pipe analogy, resistance can be thought of as a constriction or blockage in a pipe. This makes it difficult for current (or water) to pass through. Higher resistance means less current for a given voltage.

Visualization of Ohm's law

To better understand Ohm's law, let's visualize these relationships. Consider the concept of water flowing through pipes as parallel to electricity flowing through wires.

Voltage

In the visual example above, the length of the blue lines within the pipe represents the voltage. These lines push electrons (like water) through the gray pipe (wire). When the resistance is high, the pipe becomes narrower, reducing the flow of current, which is represented by the thickness of the blue lines.

Applying Ohm's law: Examples

Example 1: Calculating voltage

If the resistance of a light bulb in a circuit is 5Ω, and the current flowing through it is 2A, what is the voltage across the light bulb?

Applying Ohm's law:

V = I * R = 2A * 5Ω = 10V

Thus, the voltage across the light bulb is 10V.

Example 2: Determination of current

Suppose a resistor has a resistance of 8Ω, and a battery supplies a voltage of 16V across it. What is the current flowing through the resistor?

Rearranging Ohm's law to solve for current:

I = V / R = 16V / 8Ω = 2A

Hence the current flowing through the resistor is 2A.

Example 3: Finding resistance

When a voltage of 20V is applied to a wire, a current of 4A flows. What is the resistance of the wire?

Rearranging Ohm's law to find resistance:

R = V / I = 20V / 4A = 5Ω

Thus, the resistance of the wire is 5Ω.

Influence of material on resistance

Different materials offer different levels of resistance to current flow. Conductors such as copper and aluminum have low resistance, allowing electrons to flow easily, while insulators such as rubber and glass have very high resistance. This is why conductive materials are used to make wires, while insulating materials are used to coat them.

Resistors in the circuit

Resistors are components that apply a specific resistance to a circuit. They are used to control voltage and current levels in electronic circuits. Resistors ensure that components receive the correct voltage and current, protecting them from damage.

Series and parallel resistance

When resistors are connected in series, their resistances add up. For resistors R1, R2 and R3 connected in series, the total resistance Rtotal is given by:

Rtotal = R1 + R2 + R3

When resistors are connected in parallel, the total resistance decreases and is expressed as follows:

1/Rtotal = 1/R1 + 1/R2 + 1/R3

Let us understand the concept of resistors in series and parallel:

Series connection visualization

R1R2R3

Parallel connection visualization

R1R2R3

Understanding conductivity

The inverse of resistance is called conductivity, and it tells how well a material can conduct electrical current. Materials with high conductivity have low resistance and allow more current to flow through them. For example, silver is one of the best conductors of electricity.

Factors affecting resistance

Several factors affect the resistance of a material:

  • Type of material: Different materials naturally provide different levels of resistance.
  • Length: The longer the conductor, the greater the resistance.
  • Cross-sectional area: Wide conductors have lower resistance because they provide more space for the electrons to flow.
  • Temperature: As temperature increases, resistance also increases because the atoms in the conductor vibrate more, making it more difficult for electrons to pass through.

Importance of Ohm's law

Ohm's law is important in the design and analysis of electrical and electronic circuits. By knowing two of the three variables (voltage, current, resistance), you can easily determine the third. This helps to design safe and functional circuits.

Beyond simple circuits

While Ohm's law is straightforward, real-world applications involve complex circuits containing various components, each of which contributes to the total resistance and other electrical characteristics. Electrical engineers use Ohm's law along with Kirchhoff's laws, capacitors, and inductors to design more complex circuits.

Conclusion

Ohm's law is an essential connection in understanding electricity and circuitry. It forms the foundation of electrical engineering and electronics, making it possible to predict how voltage, current, and resistance will affect circuits and their components. Understanding these concepts is important for anyone studying or pursuing a career in the physical sciences and technology.


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Ohm's law and electrical resistance

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