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 ↓


The concept of electric current


Electricity is one of the most basic concepts in physics and is essential to modern life. But what exactly is electric current? Simply put, electric current is the flow of electrical charge. Just like water flows through pipes, electrical charges flow through conductive materials such as wires.

What is electric current?

Electric current refers to the movement of electrons, which are negatively charged particles, through a conductor. In more formal scientific terms, electric current is defined as the rate of flow of electric charges. It is measured in amperes (A), named after French physicist André-Marie Ampère.

The formula for calculating electric current (I) is given as:

I = dfrac{Q}{t}

Where:

  • I is the current in amperes (A)
  • Q is the charge in coulomb (C)
  • t is the time in seconds (s)

Nature of electric charge

To understand electric current, we must first understand electric charges. There are two types of charges: positive and negative. Electrons are negatively charged, while protons are positively charged. In a neutral atom, the number of electrons is equal to the number of protons, making the atom electrically neutral.

When electric charges move, they create an electric current. This usually occurs when the charges are free to move, such as in metals, which have free electrons that can drift when a voltage is applied.

Visual representation of electric current

Imagine a pipe filled with water. If we think of the pipe as a conductor and the water inside it as electrons, then electric current is similar to turning on a tap to make water flow through the pipe.

In this illustration:

  • This line represents a conductor (such as a copper wire).
  • The blue circles represent electrons flowing through the conductor when a voltage is applied.

Direction of current

Although the electrons themselves move in a conductor from the negative terminal to the positive terminal, conventionally the direction of electric current is considered to be from the positive terminal to the negative terminal. This is called the conventional current direction.

Conventional current direction

Types of electric current

The electric current can be either direct current (DC) or alternating current (AC).

  • Direct current (DC): In direct current, electric charge (electrons) flows in one direction. Batteries provide DC current because their direction of flow is constant.
  • Alternating Current (AC): In alternating current the electric charge changes its direction periodically. This is the type of current supplied to our homes and is suitable for transmitting electricity over long distances.

Measuring electric current

To measure electric current, an instrument called an ammeter is used, which is connected in series with the component whose electric current is to be measured. This enables the ammeter to measure the flow of charge through the component.

Factors affecting electric current

Many factors can affect how electric current flows through a circuit. These include voltage, resistance, and the nature of the material through which the current is flowing.

Voltage

Voltage, also called electric potential difference, is the force that pushes electric charges to move. Higher voltage means more force driving the current. It is measured in volts (V).

Resistance

Resistance is the opposition to the flow of electric current. It is measured in ohms (Ω). All materials have some resistance, but conductors such as copper have low resistance, allowing current to flow easily. Insulators such as rubber have high resistance, which prevents the flow of current. The concept of resistance can be compared to a narrow section in a water pipe, which reduces the flow of water.

Resistance

The relationship between voltage, current and resistance is described by Ohm's law:

V = I times R

Where:

  • V is the voltage in volts (V)
  • I is the current in amperes (A)
  • R is the resistance in ohms (Ω)

Examples of electric current in daily life

Electric current powers all kinds of devices that we use in our daily lives. From obvious examples like bulbs and radios to more complex electronics like computers and electric vehicles.

Consider a simple circuit consisting of a battery, a light bulb, and connecting wires. When the circuit is complete, the battery provides the voltage needed to push electrons through the wires and into the light bulb. The resistance of the bulb's filament causes it to heat up and emit light.

Here's another example: When you charge your mobile phone, the electric current from the charger flows into the phone's battery, replenishing its charge. The rate of charging depends on the current supplied by the charger.

Understanding electrical circuits

Electric current flows through a path called an electrical circuit. A basic electrical circuit consists of a power source (such as a battery), conductors (such as wires) and a load (such as a light bulb). The circuit must be closed for current to flow. If there is a break anywhere in the circuit, current cannot flow, and the devices in the circuit will not work.

Series and parallel circuits

There are two fundamental types of circuits: series and parallel.

  • Series circuits: In a series circuit, components are connected end to end in such a way that the same current flows through each component. If one component fails, the entire circuit breaks down. For example, old strings of Christmas lights were often wired in series.
  • Parallel circuits: In parallel circuits, components are connected at common points, and the current is divided between the branches. If one component fails, the rest continue to work. Household electrical wiring is usually parallel.

The total resistance in a series circuit is the sum of the resistances of the individual components:

R_{total} = R_1 + R_2 + R_3 + ldots

The total resistance in a parallel circuit is given by:

dfrac{1}{R_{total}} = dfrac{1}{R_1} + dfrac{1}{R_2} + dfrac{1}{R_3} + ldots

Safety aspects of electric current

While electric current is a powerful and important resource, it is essential to handle it safely. Improper use of electrical equipment can cause power failure, damage, or even personal injury. Here are some key safety tips:

  • Always ensure electrical appliances are unplugged when not in use.
  • Never touch electrical equipment with wet hands.
  • To avoid electrical shock, keep electrical appliances away from water.
  • Do not overload the electrical outlet as this may cause overheating and fire.

Conclusion

The concept of electric current is central to our understanding of electricity and magnetism. By imagining electric current as a flow of charge similar to water through a hose and using formulas such as Ohm's law, we can better understand its nature and applications. Electric current powers everything from household appliances to complex industrial machinery, making it an essential part of modern life.


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The concept of electric current

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