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Electric Current and Its Effects Class 7 Notes Science Chapter 14

Electric Current and Its Effects Class 7 Notes Science Chapter 14

Preview of the chapter 

The most practical source of energy, electricity powers many electrical appliances. It is generated at power plants and transported to houses via subterranean cables, electric pole networks, and thin wires. The movement of electricity via a conductor is known as electric current. By incorporating an electric cell or battery into a circuit, one can acquire electricity from another source. An electric cell or battery must be wired into a circuit in order to produce power. 

Introduction to Electric Current and Its Effects

Introduction to charge

  • The fundamental physical characteristics of matter, or electric charge, are what allow matter to experience a specific type of force when subjected to the effect of an electromagnetic field.
  • Charges come in two flavors: positive and negative.
  • Contrary charges attract one another while like charges repel one another.
  • Coulomb, the SI unit for electric charge, is approximately 6.2421018 e.  A single electron has a charge of 1.602 10-19 C.

Electric Circuits

A continuous conducting channel between two terminals of a cell or battery along which an electric current is flowing is known as an electric circuit. For instance, a copper wire can be used to link a cell with a positive (+) and a negative (-) terminal to a switch and to a bulb holder using another copper wire. The opposite end of the bulb holder is directly wired to the negative terminal of the cell. Electric circuit is the name for this configuration. 

Circuit Diagram

A circuit diagram is a diagram that uses the electrical symbols for the various components to demonstrate how the connections between them have been made in an electric circuit. When a switch is closed in an electric circuit, it is said to be in the ON position, and when it is open, it is said to be in the OFF position. The only way the bulb can stop glowing is if it becomes fused, which means that its filament breaks. Drawing an electric circuit by hand, including the actual designs of a cell, battery, switch, bulb, etc., is a challenging and time-consuming task.

Electric Cell and Battery

An electric cell is a frequent source of electricity for a variety of devices such as torches, radios, electric clocks and watches, toys, and so on, however a single cell is not always sufficient to power a large number of devices due to the high voltage required to power all of these gadgets. The cell delivers far less electricity than the electric supply line, for example, a single electric cell provides only 1.5 V of electricity, but electricity from the power station is supplied to our home at a very high voltage of 220 V.

Combination of Electric Cells

A battery is a collection of cells connected in series, like in a flashlight or TV remote. Since cells are frequently not arranged in a row, two or more cells connected side by side are referred to as being joined in parallel. This set is also referred to as a battery. Batteries have the unique ability to be recharged and are utilized in vehicles such as cars, buses, lorries, inverters, etc. To ensure that the cells are precisely positioned in their respective battery compartments, connections of cells/battery '+' and '-' symbols are printed on the battery.

Heating Effect of Electric Current

Conductors and insulators

  • Substances or materials that offer comparatively less opposition to electric current through them are called as conductors. Eg: copper, iron, water, etc.
  • Substances, which offer larger opposition to electric current through them are called as insulators. Eg: rubber, wood, sand, etc.
The heating effect of electric current is the production of heat in an electric device due to the flow of electric current. This happens due to the degree to which a material opposes the passage of current through itself, known as its resistance. All electrical heating devices consist of a coil of wire called an element. Factors on which the heating effect of current depends include resistance of wire, magnitude of current passed through a given wire, material of wire, length of wire, and thickness of the wire. Resistance of wire is determined by the material of the wire, length of wire, and thickness of the wire. Magnitude of current passed through a given wire is determined by the magnitude of current passed through a given wire.

Heating effects of electric current

  • An electromagnet makes up an electric bell. The circuit is completed when we press the switch.
  • The bell's operation is demonstrated below. When the switch (K) is pressed, the circuit is current.
  • When activated, the electromagnet (E) produces a magnetic field that pulls the iron strip toward it.
  • The gong or bell is struck by the striker (B).
  • The contact at (T) breaks when the striking arm (A) strikes the gong, cutting off current to the circuit.
  • The electromagnet loses its magnetic field as a result of this.
  • The striker is brought back to its initial resting position by the linked spring arm.
  • If the main switch is still pressed, the contact is reestablished, and electricity flows across the circuit.
  • Repetition of the procedure

Electric bulb and electric fuse

  • The fuse is a safety device that operates on the heating effect of current to prevent electric fires or damage to electrical appliances caused by excessive current flow.
  • It is made up of a short length of thin tin-plated copper wire with a lower melting point and higher resistance than the rest of the house's electric wiring
  • If the current in the electric wiring suddenly increases, the fuse wire heats up and melts, breaking the circuit and preventing fire and damage to various electrical appliances.
  • When a fuse blows, a new fuse must be installed in its place to restore power to the household circuit.

Magnetic Effect of Electric Current

  • then an electric current flows through a wire, the magnet-like behavior of the wire is caused.
  • The magnetic effect of current is the name given to this phenomena.
  • An electric current passing via a wire causes the compass needle to be deflected from its normal North-South position, as discovered by scientist Hans Christian Oersted.
  • A magnetic effect results from an electric current flowing along a straight wire.
  • The only way to amplify the magnetic effect is to utilize a long wire coil in place of a straight wire.
  • If a coil of wire is twisted around an iron rod and then current is run through it, the magnetic effect is boosted even further.

Lightning and magnetism

  • Air currents rise upward during thunderstorms, whereas water droplets move downhill. As a result, charges between clouds and between clouds and the earth separate.
  • Air, which is often a poor conductor, starts conducting as the magnitude of charges rises, allowing electricity to flow. This passage of charge is referred to as lightning because it is accompanied by dazzling flashes of light and thunder.
  •  Lodestones are naturally occurring magnets created by lightning.

Electro Magnet

Electromagnets

  • An electromagnet is a synthetic magnet that, when an electric current flows through it, creates a magnetic field around a conductor.
  • When there is no current flowing through the conductor, this magnetic field vanishes.
  • Electromagnets and permanent magnets differ from one another.

Difference between electromagnets and permanent magnets

  1. How they are made: Permanent magnets are made from materials like iron, cobalt, and nickel that have natural magnetic properties. Electromagnets, on the other hand, are made by wrapping a wire around a magnetic core and passing an electric current through it.

  2. Strength: Electromagnets can be much stronger than permanent magnets because the strength of an electromagnet is directly proportional to the amount of current passing through the wire. Permanent magnets have a fixed strength that cannot be changed.

  3. Magnetization: Permanent magnets are always magnetized, meaning they produce a magnetic field all the time. Electromagnets, on the other hand, are only magnetized when a current flows through the wire.

  4. Control: Electromagnets can be turned on and off by controlling the flow of electric current. Permanent magnets cannot be turned off or controlled in the same way.

  5. Applications: Electromagnets are used in a wide variety of applications, including electric motors, generators, MRI machines, and speakers. Permanent magnets are used in applications where a constant magnetic field is needed, such as in refrigerator magnets, compasses, and electric guitar pickups.

Electric Bell

Hazards of electricity

  • Electricity is a risk since it can heat up and start a fire, which could result in fatalities.
  • It's important to adequately insulate electrical circuits. Wires can short circuit if the insulation fails and they come into contact with one another, which could result in electric shocks if touched.

Electric bell

  • An electromagnet makes up an electric bell. The circuit is completed when we press the switch.
  • The bell's operation is demonstrated below. When the switch (K) is pressed, the circuit is current.
  • When activated, the electromagnet (E) produces a magnetic field that pulls the iron strip toward it.
  • The gong or bell is struck by the striker (B).
  • The contact at (T) breaks when the striking arm (A) strikes the gong, cutting off current to the circuit.
  • The electromagnet loses its magnetic field as a result of this.
  • The striker is brought back to its initial resting position by the linked spring arm.
  • If the main switch is still pressed, the contact is reestablished, and electricity flows across the circuit.
  • Repetition of the procedure

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