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


Current electricity means the flow of electric charge in a circuit. It is a fundamental concept in physics that plays a vital role in our daily lives, powering a wide variety of devices and systems. In this comprehensive guide, we will explore the essential components, principles, and applications of current electricity.

Basic concepts

At the core of current electricity is the idea that electrical charge moves through conductors. Conductors are substances that allow the easy flow of electrical charge. Metals such as copper and aluminum are good examples of conductors. On the other hand, insulators are substances that do not allow electrical charge to flow freely. These include substances such as rubber and glass.

Electric charge

Electric charge is a fundamental property of matter. Charges are either positive or negative. This property is carried by subatomic particles: protons have a positive charge, while electrons have a negative charge. The interaction between charges follows this law: like charges repel each other, while opposite charges attract each other.

Electric current

Electric current is the flow of electric charge. In most cases, it is the flow of electrons through a conductor. Current is measured in amperes (A), which indicates the amount of charge flowing past a point in a circuit in a given time. Electric current can be direct (DC) or alternating (AC).

Direct Current (DC): In DC the electric charge flows in only one direction, commonly found in batteries.

Alternating Current (AC): In AC, electric charge flows back and forth, and periodically changes direction, as seen in household power supplies.

Voltage

Voltage, also known as electric potential difference, is the force that pushes electric charges through a conductor. It is measured in volts (V). Voltage is essentially the energy per unit charge and is required to create and maintain electric current. Higher voltage means there is more potential energy available to move charges.

Resistance

Resistance is the opposition to the flow of electric current. It is measured in ohms (Ω). Every conductor has some resistance that impedes the movement of electrons. The amount of resistance depends on factors such as the conductor's material, length, cross-sectional area, and temperature. Ohm's law is fundamental to understanding resistance:

 V = I × R

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

Components of the circuit

A circuit is a complete path for the flow of electricity. It consists of several basic components, including:

  • Battery: A source of voltage that provides the energy needed to move charges in a circuit.
  • Conductors: Usually wires that provide a path for electric current.
  • Load: A device that consumes electrical energy, such as a bulb or motor, and converts it into other forms of energy.
  • Switch: A component that can open or close a circuit, controlling the flow of electricity.

Visual example: Simple circuit

Battery Bulb Change

In this simple circuit, the battery provides the voltage, the wires serve as conductors, the bulb is the load, and the switch can open or close the circuit.

Types of circuits

There are two main types of electrical circuits: series circuits and parallel circuits. Let's take a look at their characteristics.

Series circuit

In a series circuit, components are connected end-to-end, forming a single path for electric current. If one component fails, the entire circuit is disrupted. An example of this is a series of old-style Christmas lights. The total resistance in a series circuit is the sum of the individual resistances:

 R total = R 1 + R 2 + R 3 + ... + R n

The current flowing through each component is the same, but the voltage across each component is different, which is equal to the total voltage provided by the source.

Visual example: Series circuit

R1 R2 Battery Change

In this series circuit, each resistor (R1 and R2) is connected one after the other so that the same amount of current flows through them.

Parallel circuit

Parallel circuits have multiple paths for electric current to flow. In this configuration, failure of one path does not stop the flow of electric current in the other paths. Most household lighting systems are parallel circuits. The total resistance in a parallel circuit is given by:

 1/R total = 1/R 1 + 1/R 2 + 1/R 3 + ... + 1/R n

The voltage across each component is the same, but the current may vary. The total current is the sum of the currents passing through each parallel path.

Visual example: Parallel circuit

R1 R2

In this parallel circuit, each resistor (R1 and R2) is connected so that current can flow through more than one path.

Measuring current, voltage and resistance

Ammeter

An ammeter measures the current flowing through a conductor or circuit. It is designed to be connected in series with the circuit so that the current passes through the device. Ammeters have very low resistance to ensure that they do not cause any significant change in the flow of current.

Voltmeter

A voltmeter measures the voltage at two points in a circuit. It is connected in parallel with the component or part of the circuit whose voltage you want to measure. Voltmeters have high resistance to ensure that they draw minimum current.

Ohmmeter

An ohmmeter measures the resistance of a component in a circuit. It is generally used when the circuit is closed to avoid false readings due to current flow. Component resistance helps determine and diagnose circuit behavior.

Multimeter

The multimeter is a versatile instrument that combines the functions of an ammeter, voltmeter, and ohmmeter into a single device. It can measure current, voltage, and resistance, making it an essential tool in electrical and electronic work.

Applications of electric current

Current electricity has many applications in our modern world. Here are some examples:

  • Lighting: Electric currents power a variety of light sources, from household bulbs to street lights.
  • Heating: Electric heaters and stoves convert electrical energy into heat, which is used in homes and industry.
  • Transportation: Electric vehicles use electrical energy stored in batteries to run the motors.
  • Communications: Telephones, the Internet, and other communications devices rely on electronic circuits powered by electric current.
  • Computing: Computers, smartphones, and servers rely on electrical currents for processing and storing data.

Safety precautions

Although existing electricity is beneficial, it is important to use it with caution. Here are some safety tips:

  • Avoid water when working with electricity, as it can conduct electricity, increasing the risk of shock.
  • Turn off appliance before inspecting or servicing electrical components.
  • Use insulated tools to prevent accidental contact with live parts.
  • Always follow the manufacturer's guidelines when using power tools and equipment.
  • Make sure circuits are properly grounded to prevent short circuits and electrical fires.

Current electricity is a fascinating and powerful phenomenon, integral to modern technology and everyday life. By understanding the principles and applications of current electricity, we can harness its potential safely and effectively.


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Current Electricity

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