Current Electricity: Madhyamik Physical Science

• Current electricity is the study of electric charges in motion. It is one of the most important topics in Madhyamik Physical Science, as it explains how electric circuits work and how electrical devices function. Here, we will cover the main concepts and formulas of current electricity, such as electric current, potential difference, resistance, Ohm’s law, and electric power.
• Electric Current

Electric current is the rate of flow of electric charge through a conductor. It is measured in amperes (A), which is defined as one coulomb (C) of charge passing through a point in one second (s). The direction of electric current is taken as the direction of positive charge flow, even though in most cases it is actually the negative charges (electrons) that move.

The electric current (I) through a conductor depends on two factors: the potential difference (V) across the conductor and the resistance (R) of the conductor. The potential difference is the work done per unit charge to move a charge from one point to another in an electric field. The resistance is the opposition to the flow of current due to collisions of charges with atoms or molecules in the conductor. The relationship between these three quantities is given by Ohm’s law:

• Ohm’s Law

  Ohm’s law states that the potential difference across a conductor is directly proportional to the current through it, provided that the physical conditions such as temperature and pressure remain constant. The constant of proportionality is called the resistance of the conductor. Ohm’s law can be written as:
   V = IR

  where V is the potential difference in volts (V), I is the current in amperes (A), and R is the resistance in ohms (\Omega).

  Ohm’s law can be verified experimentally by using a simple circuit consisting of a battery, a resistor, an ammeter, and a voltmeter. By varying the resistance or the battery voltage, we can observe that the current changes proportionally to the potential difference.

• Resistance

  Resistance is a measure of how much a conductor opposes the flow of electric current.

  • It depends on several factors, such as:
    – The material of the conductor: Different materials have different resistivities (\rho), which are intrinsic properties that determine how easily charges can move through them. Metals have low resistivities, while insulators have high resistivities.
    – The length of the conductor: The longer the conductor, the more collisions the charges have to face, and hence more resistance.
    – The cross-sectional area of the conductor: The larger the area, the more space for charges to flow, and hence less resistance.
    – The temperature of the conductor: The higher the temperature, the more vibrations of atoms or molecules in the conductor, and hence more collisions and more resistance.
• Electric Power

  Electric power is the rate at which electrical energy is transferred by an electric circuit. It is measured in watts (W), which is defined as one joule (J) of energy transferred per second (s). The electric power (P) delivered by a source or consumed by a device can be calculated by using this formula:
  P = VI
  where V is the potential difference across the source or device in volts (V), and I is the current through it in amperes (A).

  The electric power can be used to calculate other quantities such as electrical efficiency, electrical cost, and electrical safety.

• Heating Effect of Electric Current

Electric current is the flow of electric charges in a conductor. When electric current passes through a conductor, some of the electrical energy is converted into heat energy. This is called the heating effect of electric current.

• • Factors Affecting the Heating Effect: The amount of heat produced by a current-carrying conductor depends on three factors:
    • – The resistance of the conductor: A higher resistance produces more heat because more energy is required to overcome the resistance and maintain the current flow.
    • – The time for which the current flows: The longer the time, the larger the amount of heat produced, because more electrical energy is supplied to the conductor.
    • – The amount of current: The higher the current, the larger the amount of heat generated, because more electric charges pass through the conductor and collide with its atoms.

The mathematical expression for the heat produced by a current-carrying conductor is given by:

H = I^2 * R * t

where H is the heat produced, I is the current, R is the resistance, and t is the time.

• • Applications of Heating Effect: The heating effect of electric current has many practical applications in our daily life. Some examples are:
    • – The electric bulb: The filament of an electric bulb is made of a high-resistance material like tungsten, which glows when heated by electric current. The filament is enclosed in a glass bulb filled with an inert gas to prevent it from burning.
    • – The electric iron: An electric iron has a coil of wire inside it, which acts as a heating element. When current passes through the coil, it becomes hot and transfers heat to the metal plate of the iron. A thermostat is used to regulate the temperature of the iron by breaking and making the circuit.
    • – The electric heater: An electric heater works on a similar principle as an electric iron, but it has a larger coil and a fan to circulate hot air in the room. A circuit breaker is used to prevent overheating and fire hazards.
    • – The electric fuse: An electric fuse is a safety device that protects electrical appliances from damage due to excessive current. It consists of a thin wire of low melting point metal like copper or zinc, which melts and breaks the circuit when too much current flows through it.