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Electric Current and its Effects Notes



ELECTRIC CURRENT AND ITS EFFECTS

Electrical energy is the most useful form of energy as it can easily be converted into various other forms of energy such as heat energy, light energy, mechanical energy and chemical energy.
 

Electric current:

The flow of charges through a circuit is called electric current. The SI unit of electric current is ampere and donated by A. The direction of the electric current is conventionally from the positive terminal to the negative terminal of a cell.
 

Electric circuit:

An electric circuit is a complete path for the flow of electric current. A circuit consists of an electric cell  devices which use the electrical energy, a switch and connecting wires. These all are called components of the circuit or circuit elements.
  • If any part of a circuit is broken, electric current does not flow through it and such a circuit is called an open circuit.
  • If there are no breaks in a circuit, it provides a closed for the flow of electric current and such a circuit is called a closed circuit.
  • Electric current can flow only through closed circuit
 

Components of an electric circuit:

 
Cell or battery:
  • A cell is a source of current.
  • It has a positive and a negative terminal.
  • When two or more cells are connected such that the positive terminal of one cell touches the negative terminal of the other, it forms a battery, but they have to be connected in a proper manner for electricity to flow through the circuit. They can be connected in series or in parallel.
 
Switch:
  • A switch is used to close or open a circuit.
  • When the switch is off, the circuit is open and no current flows through it.
  • When the switch is on the circuit is closed allowing current to flow.
 
Electrical appliance:
  • An electrical appliance is a device that uses the current flowing through it to function.
  • Electric bulbs, electric iron, fans, electric motors are some commonly used electrical appliances in our daily life.
 
Wires:
  • Wires connect the element of the electric circuit. They are made up of materials that are good conductors of electricity such as copper.
 

Connecting cells in series:

When the cells are connected in series, the positive (+) terminal of one cell is connected to the negative (-) terminal of the other cell. When you complete connecting cells, you will have a positive terminal at one end and the negative terminal at the other end.

Connecting cells in parallel:

When cells are connected in parallel, the light terminals of cells are linked together. This means that the positive terminal or negative terminal of all the cells are connected together.

 

Circuit diagram:

A schematic diagram that represents an electric circuit using the standard symbols of the components used in the circuit is called a circuit diagram.

 
Table of standard symbols component of circuit

 

Light emitting diode (LED)

  • Nowadays, Light emitting diodes (LEDs) are used instead of an electric bulb because they consume less electricity, do not produce heat, have very long life and are almost unbreakable.
  • An LED allows electric current to follow in one direction only.
  • LED cannot tolerate even a small change in electric current. A circuit with an LED therefore requires an appropriate resistor. The resistor regulates the flow of electric current and protects the LED.



Heating effect of electric current:

When electric current is passed through a conductor, it produces heat in the conductor and this effect is called the heating effect of electric current.
  • Electric iron, immersion heaters, hot plates, geysers, electric kettles are some of the electric appliances used, which work on the heating effect of the electric current.
  • All the devices have a coil of wire called an element. The heating element is made up of metal alloy called nichrome (alloy of 80% nickel and 20% chromium). Nichrome wire have high resistance to electric current and can withstand high temperatures. Due to this property, it is a good material for making heating elements.
  • When the appliance is switched on, the element becomes red hot and give out heat.
  • The amount of heat generated by a metal conductor (wire) depends on the strength of electricity flowing through it, the type of metal and on the length and thickness of the conductor.

 

What makes a bulb glow:

  • A bulb glows due to the heating effect of electric current.
  • A bulb has a partial vacuum, argon gas and a thin filament of tungsten.
  • Tungsten metal has a very high resistance and very high melting point.
  • When an electric current pass through the filament, due to its high resistance, its heat up quickly to about 2500 degree Celsius.
  • At this temperature, the tungsten filament begins to glow and emits light.

Electric fuse:

A fuse or an electric fuse is a safety device made of a material with low melting point. it is used to protect the electric circuit and devices in the circuit from the excess current passing through them.
 
How does a fuse work:
  • Electric fuse works on the principle of the heating effect of electric current.
  • The quantity of heat produced in a conductor by a current depends on the amount of current flowing through the conductor.
  • A fuse is a thin wire of short length that melts easily when heated.
  • When the fuse wire breaks due to heating by excess amount of current, the circuit breaks and becomes an open circuit; no current can flow through it and the devices in the circuit are safe.
  • The fuse wire is made from an alloy of tin and lead and has a low melting point. Hence, it melts easily when more than the designated amount of current flows through the circuit.
  • The main characteristic of a fuse wire are that it must have low melting point and relatively high resistance.

 

Magnetic effect of electric current:

A current carrying conductor produces the same effect as produced by the magnetic field of a magnet. This effect of current is called the magnetic effect of electric current.

Solenoid:

  • A cylindrical- shaped coil that exhibits magnetic properties similar to that of a bar magnet when current is passed through it is called a solenoid.
  • The strength of the magnetic field shown by a solenoid depends on the amount of current flowing through it and the number of turns of the coil.

 

Electromagnet:

  • An Electromagnet is a device that act as a magnet when a current flows through its coil.
  • It consists of a magnetic material such a soft iron piece and the coil of insulated copper wire tightly wound around it.
  • The material on which the insulated wire is wound is called its core.
  • It is a temporary magnet that loses its magnetic property when the current through the circuit is withdrawn.

 
Applications of electromagnet:
Electromagnets have a variety of applications in industries and in our daily life. Some of the these are listed below:
  • In electric cranes to lift scrap iron
  • As armature of electric motors
  • In electronic devices such a television, radio and tape recorder
  • In magnetic levitation trains, mechanical relay circuits and electric bells
  • In CT/ MRI scanning for medical diagnosis.

Electric bell:

It consists of an electromagnet and armature made of thick iron bar fixed on a spring, a make-and-break arrangement with the screw S and an iron strip P.

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Reference Books for class 7 Science

Given below are the links of some of the reference books for class 7 math.

  1. Science for Class 7 by Lakhmir Singh
  2. Science Foundation Course For JEE/NEET/NSO/Olympiad - Class 7
  3. CBSE All In One Science Class 7 by Arihant Experts (Author)
  4. IIT Foundation Physics, Chemistry & Maths for Class 7

You can use above books for extra knowledge and practicing different questions.



Class 7 Maths Class 7 Science





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