Grade 10
  1. Mechanics  1.1. Dynamics  1.1.1. Motion in one dimension  1.1.2. Motion in two dimensions  1.1.3. Displacement and Distance  1.1.4. Speed and Velocity  1.1.5. Acceleration  1.1.6. Graphical representation of motion  1.1.7. Equations of motion  1.1.8. Free fall and acceleration due to gravity  1.1.9. Projectile motion  1.1.10. Relative speed  1.2. Dynamics  1.2.1. Newton's Laws of Motion  1.2.2. Inertia and mass  1.2.3. Force and its types  1.2.4. action and reaction force  1.2.5. Friction and its effects  1.2.6. Coefficient of friction  1.2.7. Circular motion  1.2.8. Centripetal force and centripetal acceleration  1.2.9. Momentum and Impulse  1.2.10. Conservation of momentum  1.2.11. Newton's third law and applications  1.3. Work, Energy and Power  1.3.1. Work done by the force  1.3.2. Work–energy theorem  1.3.3. Kinetic energy  1.3.4. Potential energy  1.3.5. Mechanical energy  1.3.6. Energy Conservation  1.3.7. Power and efficiency  1.3.8. Renewable and non-renewable energy sources  1.4. Gravitational force  1.4.1. Newton's law of universal gravitation  1.4.2. Gravitational field and field strength  1.4.3. Acceleration due to gravity on different planets  1.4.4. Kepler's laws of planetary motion  1.4.5. Orbits and satellites  1.4.6. Weight and apparent weight  1.4.7. Gravitational potential energy
  2. Properties of matter  2.1. States of matter  2.1.1. Solid, liquid and gas  2.1.2. Molecular structure of matter  2.1.3. Intermolecular forces  2.1.4. Plasma and Bose–Einstein condensate  2.2. Pressure  2.2.1. Definition of Pressure  2.2.2. Pressure in liquids  2.2.3. Atmospheric pressure  2.2.4. Pascal's principle  2.2.5. Archimedes' Principle and Buoyancy  2.2.6. Surface tension and capillarity  2.3. Elasticity  2.3.1. Hooke's law  2.3.2. Stress and strain  2.3.3. Elastic Limit and Modulus of Elasticity  2.3.4. Applications of Elasticity
  3. Thermal physics  3.1. heat and temperature  3.1.1. Difference Between Heat and Temperature  3.1.2. Temperature scale  3.1.3. Thermal expansion  3.1.4. Thermal equilibrium  3.2. Heat transfer  3.2.1. Conductivity  3.2.2. Convection  3.2.3. Radiation  3.2.4. Insulation and its applications  3.3. Thermal properties of matter  3.3.1. Specific heat capacity  3.3.2. Latent heat and phase change  3.3.3. Boiling and Melting Point  3.3.4. Heat engines and refrigeration  3.4. Laws of Thermodynamics  3.4.1. Zeroth law of thermodynamics  3.4.2. First law of thermodynamics  3.4.3. Second law of thermodynamics  3.4.4. Carnot cycle
  4. Waves and optics  4.1. Nature and properties of waves  4.1.1. Types of waves in nature and properties of waves  4.1.2. Transverse and longitudinal waves  4.1.3. Wave parameters  4.1.4. Reflection and refraction of waves  4.1.5. Superposition and Interference  4.1.6. Standing Waves and Resonance  4.1.7. Doppler effect  4.2. Sound waves  4.2.1. Characteristics of sound waves  4.2.2. Speed of sound in different mediums  4.2.3. Applications of sound waves  4.2.4. Ultrasound and its uses  4.3. Light Waves and Optics  4.3.1. Nature of light  4.3.2. Reflection of light  4.3.3. Laws of reflection  4.3.4. Mirrors and Image Formation  4.3.5. Refraction of light  4.3.6. Snell's Law  4.3.7. Lenses and Image Formation  4.3.8. Total internal reflection and critical angle  4.3.9. Optical fibre  4.4. Optical Instruments  4.4.1. Microscope  4.4.2. Telescope  4.4.3. Human eye and vision defects  4.4.4. Camera and its working principle
  5. Electricity and Magnetism  5.1. Electrostatics  5.1.1. Electric charge and its properties  5.1.2. Conductors and Insulators  5.1.3. Coulomb's law  5.1.4. Electric field and field lines  5.1.5. Electric potential and potential difference  5.1.6. Capacitors and Capacitance  5.2. Current Electricity  5.2.1. Electric current and its measurement  5.2.2. Ohm's law  5.2.3. Resistance and resistivity  5.2.4. Series and Parallel Circuits  5.2.5. Electric power and energy  5.2.6. Kirchhoff's Laws  5.3. Magnetism and Electromagnetism  5.3.1. Magnetic field and field lines  5.3.2. Magnetic effects of electric current  5.3.3. Electromagnetic induction  5.3.4. Faraday's laws of electromagnetic induction  5.3.5. Transformers and Applications  5.3.6. AC and DC current
  6. Modern Physics  6.1. Nuclear physics  6.1.1. Structure of the atom  6.1.2. Bohr's atomic model  6.1.3. Electron Energy Levels  6.1.4. X-rays and applications  6.2. Radioactivity  6.2.1. Types of radiation  6.2.2. Half-life and radioactive decay  6.2.3. Nuclear reactions and applications  6.2.4. Fission and Fusion  6.3. Quantum physics  6.3.1. Wave–particle duality  6.3.2. Photoelectric effect  6.3.3. Energy quantization  6.3.4. Heisenberg's uncertainty principle
  7. Electronics and Communication  7.1. Semiconductors  7.1.1. Conductors, Insulators and Semiconductors  7.1.2. Diodes and their applications  7.1.3. Transistors and Logic Gates  7.1.4. LEDs and photodiodes  7.2. Communication Systems  7.2.1. Basics of communication  7.2.2. Analog and digital signals  7.2.3. Wireless and optical fibre communication  7.2.4. Radio Waves and Modulation

Grade 10 → Electricity and Magnetism → Current Electricity ↓


Resistance and resistivity


To understand electricity, it is important to explore how electric currents flow through different materials. Two fundamental concepts in this study are resistance and resistivity. They help us understand how materials impede the flow of electric current, affecting the effectiveness of electronic devices.

What is resistance?

Resistance is a measure of the opposition to the flow of electric current through a conductor. It is determined by the material of the conductor and its physical properties. The symbol for resistance is R, and it is measured in ohms (Ω).

Ohm's law is very important for understanding resistance. It states that:

V = I * R

Where V is the voltage across the conductor, I is the current flowing through the conductor, and R is the resistance of the conductor.

Visual example of resistance

Conductor

This diagram shows a simple conductor with current flowing from left to right. The grey area shows the material through which the current is passing, and the red circles indicate the connection points for the current. The length and thickness of the grey area can indicate how the resistance may change - the thicker or shorter the conductor, the lower the resistance will usually be.

Factors affecting resistance

The resistance in a conductor is affected by the following factors:

Material

Different materials have different inherent properties, which affect their ability to conduct electric current. Metals generally have low resistance because they have more free electrons that can move easily. In contrast, materials such as rubber and wood have high resistance.

Length

The resistance of a conductor is directly proportional to its length. This means that if you increase the length of the conductor, its resistance also increases. You can imagine this like a long hallway - the longer the path, the more opportunities for obstacles (such as collisions within the conductor).

Cross sectional area

Resistance is inversely proportional to the cross-sectional area of the conductor. A wide conductor has a larger area for current to flow through, which reduces resistance. You can think of it like a wide road that allows more cars to pass at once.

Temperature

Resistance generally increases as the temperature increases. Higher temperatures cause the atoms of the conductor to vibrate more, creating more obstacles in the path of free electrons, which increases the resistance.

What is resistivity?

Resistivity is a fundamental property of materials that describes how strongly a material opposes the flow of electric current. Unlike resistance, which depends on the dimensions of the conductor, resistivity (symbolized by ρ) is an intrinsic property of the material. It is measured in ohm-meters (Ω m).

The resistivity of a material is defined by the formula:

r = ρ * (l/a)

Where R is resistance, ρ is resistivity, L is the length of the conductor, and A is the cross-sectional area.

Visual example of resistivity

Material A Material B

This diagram compares two different materials. Despite having the same shape, materials A and B have different resistivities, resulting in different levels of resistance for the same current flow.

Practical Applications

Choosing the right material

When designing electrical circuits, engineers choose materials based on resistivity. For example, copper is widely used in electrical wiring because it has a low resistivity, which allows for the efficient transmission of electrical energy.

Electronic devices

Components such as resistors are specifically designed to provide a precise resistance value to control the flow of current within a circuit. Resistors are selected based on their resistance to meet the specific requirements of a circuit.

Example calculation

Calculation of resistance

Suppose we have a copper wire 10 meters long and its cross-sectional area is 0.5 square millimeters (0.0005 m²). Assuming that the resistivity of copper is about 1.68 * 10 -8 Ω·m, the resistance of the wire can be calculated using the resistivity formula:

r = ρ * (l/a)

On substituting the values, we get:

R = (1.68 * 10 -8 Ω m) * (10 m / 0.0005 m 2 )

This calculation gives the resistance:

R = 0.336 Ω

Understanding voltage and current

Imagine a circuit where the calculated resistance is part of a system with a 5 volt supply. Using Ohm's law, we can determine the current flowing in the system:

V = I * R

Rearranging the formula to solve for current (I), we get:

I = V/R = 5V / 0.336Ω

which gives a stream of approximately:

I ≈ 14.88 A

Summary of resistance and resistivity concepts

In short, resistance and resistivity are central to our understanding of how electricity behaves in different materials and how we can effectively control and use it in a variety of applications. Materials with low resistance and resistivity are ideal for situations where it is necessary to maintain a strong current, while high resistance can be useful in controlling the flow of current within electronic circuits.

Resistance and resistivity play a vital role in everything from the power grids that supply energy to homes to the intricate design of circuit boards in computers and other electronic devices. Knowledge of how to manipulate these properties is a powerful tool for engineers and scientists around the world.


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Resistance and resistivity

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