Grade 9
  1. Mechanics  1.1. Motion  1.1.1. Types of motion  1.1.2. Distance and displacement  1.1.3. Speed and Velocity  1.1.4. Acceleration  1.1.5. Graphical representation of motion  1.1.6. Equations of motion  1.1.7. Uniform and non-uniform motion  1.1.8. Free fall and acceleration due to gravity  1.1.9. Relative speed  1.1.10. Circular motion  1.2. Laws of force and motion  1.2.1. The concept of force  1.2.2. newton's first law of motion  1.2.3. Newton's second law of motion  1.2.4. Newton's third law of motion  1.2.5. Inertia and types of inertia  1.2.6. Motion  1.2.7. Conservation of momentum  1.2.8. Application of Newton's laws in daily life  1.2.9. Types of Forces (Contact and Non-Contact)  1.2.10. Friction and its effects  1.3. Gravitational force  1.3.1. Newton's law of universal gravitation  1.3.2. Importance of Gravitational Force  1.3.3. Acceleration due to gravity  1.3.4. Free fall and weightlessness  1.3.5. Mass and weight  1.3.6. Variation of g with height and depth  1.3.7. Kepler's laws of planetary motion  1.3.8. Satellites and their orbits  1.4. Work, Energy and Power  1.4.1. Concept of work  1.4.2. Positive and negative actions  1.4.3. Work done by constant and variable force  1.4.4. Energy and its forms  1.4.5. Kinetic energy and potential energy  1.4.6. Law of conservation of energy  1.4.8. Commercial unit of energy  1.4.9. Work–energy theorem  1.5. Simple machines  1.5.1. Types of simple machines  1.5.2. Mechanical advantage  1.5.3. Machine efficiency  1.5.4. Levers and their types  1.5.5. Pulleys and Inclined Planes  1.5.6. Gears and their uses
  2. Properties of matter  2.1. States of matter  2.1.1. Solids, liquids and gases  2.1.2. Properties of different states of matter  2.1.3. Change in state of matter  2.1.4. Plasma and Bose–Einstein condensate  2.2. Density and pressure  2.2.1. Concept of density and relative density  2.2.2. Pressure in solids, liquids and gases  2.2.3. Pascal's law and its applications  2.2.4. Atmospheric pressure and its variations  2.2.5. Surface tension and capillarity  2.3. Buoyancy and Archimedes' principle  2.3.1. Buoyant force  2.3.2. Archimedes principle  2.3.3. Applications of Archimedes' Principle  2.3.4. floating and sinking objects  2.3.5. Theory of Flotation and Archimedes' Principle
  3. Heat and Thermodynamics  3.1. Temperature and heat  3.1.1. Concept of heat and temperature  3.1.2. Temperature measurement  3.1.3. Temperature scales  3.2. Heat transfer  3.2.1. Conduction of heat  3.2.2. Convection of heat  3.2.3. heat radiation  3.2.4. Applications of heat transfer  3.2.5. Thermal conductivity  3.3. Thermal expansion  3.3.1. Expansion of solids, liquids and gases  3.3.2. Abnormal expansion of water  3.3.3. Applications of Thermal Expansion  3.4. Specific heat capacity and latent heat  3.4.1. Concept of specific heat capacity  3.4.2. Measurement and applications of specific heat  3.4.3. Latent heat of fusion and vaporization  3.4.4. Heat Engines and Efficiency
  4. Waves and sound  4.1. Waves and their types  4.1.1. Mechanical and electromagnetic waves  4.1.2. Longitudinal and Transverse Waves  4.1.3. Properties of Waves  4.1.4. Wavelength, frequency and speed of the wave  4.1.5. Superimposition of waves  4.2. Sound waves  4.2.1. Nature and transmission of sound  4.2.2. Speed of sound in different mediums  4.2.3. Reflection of sound and echo  4.2.4. Sonar and ultrasound  4.2.5. Resonance and pulsation  4.3. Sound characteristics  4.3.1. Intensity, loudness and quality of sound  4.3.2. Doppler effect in sound
  5. Lighting and Optics  5.1. Reflection of light  5.1.1. Laws of reflection  5.1.2. Reflection from a plane mirror  5.1.3. Reflection from a spherical mirror  5.1.4. Image formation by concave and convex mirrors  5.1.5. Applications of Reflection  5.2. Refraction of light  5.2.1. Laws of refraction  5.2.2. Refractive index  5.2.3. Refraction through a glass slab  5.2.4. Refraction in water and air  5.2.5. Lenses and their types  5.2.6. Image formation by convex and concave lenses  5.2.7. Total internal reflection and its applications  5.3. Dispersion and scattering of light  5.3.1. Spectrum of white light  5.3.2. Prisms and Dispersion  5.3.3. Tyndall effect and blue sky
  6. Electricity and Magnetism  6.1. Electric charge and static electricity  6.1.1. The concept of electric charge  6.1.2. Charging by friction, contact and induction  6.1.3. Electroscope and its working  6.2. Current Electricity  6.2.1. The concept of electric current  6.2.2. Ohm's Law and Resistance  6.2.3. Factors affecting resistance  6.2.4. Series and Parallel Circuits  6.2.5. Heating effect of electric current  6.2.6. Electric power and energy  6.3. Magnetism  6.3.1. Natural and artificial magnets  6.3.2. Properties of magnets  6.3.3. Earth's magnetism  6.3.4. Magnetic field and field lines  6.3.5. Electromagnets and their applications
  7. Modern Physics  7.1. structure of the atom  7.1.1. Atomic Structure and Subatomic Particles  7.1.2. Electrons, Protons, and Neutrons  7.1.3. Rutherford and Bohr model  7.2. Radioactivity  7.2.1. Types of radioactive emissions  7.2.2. Half-life and radioactive decay  7.2.3. Uses and Hazards of Radioactivity
  8. Space science and astronomy  8.1. The universe and its components  8.1.1. Stars and galaxies  8.1.2. Planets and Solar System  8.2. Satellites  8.2.1. Natural and artificial satellites  8.2.2. Use of satellites

Grade 9 → Electricity and Magnetism → Current Electricity ↓


Heating effect of electric current


In simple words, the heating effect of electric current is an important phenomenon in which electrical energy is converted into heat energy. This effect is commonly used in appliances such as heaters, toasters, and electric ovens.

When electric current passes through a conductor, heat is generated. This is due to the resistance faced by electric charges as they pass through the conductor. The higher the resistance, the more heat is generated. Let's understand this concept in more depth to understand how it works and how it is used in everyday devices.

The concept of electrical resistance

To understand the heating effect, we must first understand the concept of electrical resistance. Electrical resistance is the resistance that a material offers to the flow of electric current. The unit of resistance is the ohm, represented by the symbol Ω.

When we say a material has high resistance, it means that it offers a lot of resistance to the flow of charges, while low resistance means that it is easy for current to flow through the material.

Formula of heat generated

The amount of heat generated by an electric current in a conductor can be calculated using Joule's law. This law states that the heat generated in a conductor is directly proportional to the square of the current, the resistance of the conductor, and the time the current flows. The formula is given as:

H = I 2 * R * t

Where:

  • H is the heat produced in joules (J).
  • I is the current in amperes (A).
  • R is the resistance in ohms (Ω).
  • t is the time in seconds (s).

Visualization of current and resistance

Let us understand the concept of electric current passing through a conductor with resistance using a simple diagram.

Battery Obstructions

In this diagram, the blue circles represent electrons moving through a conductor, experiencing resistance which causes heat to be generated.

Practical example

Example 1: Electric heater

Electric heaters use the heating effect of current. When electricity flows through a coil of high resistance wire in the heater, it heats up and emits heat to the surrounding area.

Example 2: Incandescent light bulb

In an incandescent bulb, electricity passes through a tungsten filament, which has a very high resistance. Due to this resistance, the filament heats up and emits light.

Example 3: Electric iron

In an electric press, when electric current passes through a resistance coil or strip, heat is generated which is used to press clothes.

Factors affecting the heating effect

Several factors affect the amount of heat generated in a conductor:

  • Current: More current flow results in more heat generation.
  • Resistance: Higher resistance in a conductor causes more heat to be generated.
  • Time: The longer the current flows, the more heat will be generated.

Mathematical example

Let us take a calculation example to see how the heating effect is calculated in a practical situation:

Suppose a current of 2 A flows through a 3 Ω resistor for 10 seconds. How much heat is generated then?

H = I 2 * R * t = 2 2 * 3 * 10 = 4 * 3 * 10 = 120 J

Therefore, 120 joules of heat is generated.

Applications of heating effect

The heating effect is used in a variety of devices and applications, including:

  • Electric furnaces: Used in the manufacturing industry to melt metals and other substances.
  • Soldering iron: Used in electronics to join components together.
  • Electric stove: Used in cooking appliances to produce heat required to prepare food.

Security considerations

Although the heating effect is useful, it can also be dangerous if not managed properly:

  • Excessive heat can damage electrical equipment and cause fire.
  • Overloading a circuit can cause the wires to overheat, creating a potential hazard.

Reducing heat loss

Reducing heat loss in electrical circuits is often important to improve efficiency. Some strategies are as follows:

  • Using low resistance materials for wires.
  • Designing circuits to minimize unnecessary electric current.
  • Using proper insulation to prevent heat from escaping.

Conclusion

The heating effect of electric current is an important principle in physics and plays a vital role in many everyday devices and industrial processes. Understanding this concept helps us design and use devices that rely on electric heating safely and efficiently.


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Heating effect of electric current

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