Electrical Circuits

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We know that electric current is the flow of electrons through a conductor. An electric circuit provides a closed-loop or a pathway for electric current to flow.

An electric circuit includes –

  1. A device that gives energy to the electrons for electric current to flow, such as a battery or a generator.
  2. A device or an appliance that consumes the electric current like an electric bulb, a computer, or a heater.
  3. Connecting wires for transmitting the electric current.

 The point where these electrons enter an electrical circuit is called the source of electrons and their exit point is called the return as the electrons always end up at the source when they complete the path.

1. BATTERY OR CELL –

A battery is a collection of cells. A cell is a single unit that converts chemicals stored in it into electricity. It produces voltage or the force that drives electric current through the circuit. It produces the flow of electrons. A cell stops functioning when the chemicals present in it get over. It needs to be replaced or recharged after that. A battery has two terminals- a positive terminal (top) and a negative terminal (bottom). A cell and a battery are represented as shown beside.

 

When we connect these two terminals with a connecting wire, a circuit is formed and electrons start to flow from the negative terminal towards the positive terminal. However, the direction of flow of electric current is in the reverse direction and it flows from the positive to the negative terminal.

2. ELECTRIC BULB

An electric bulb is a simple device and thus, we will be using its example. It is built in such a way that when it is connected to a circuit the connecting wires inside it join the circuit, completing the pathway. The part of the bulb that glows is called a filament and is made up of a special metal that gets heated until it starts to glow. For e.g. the filament in the bulb below is made of tungsten. When the filament breaks, it breaks the circuit, stopping the flow of electric current and thus, the bulb stops glowing. An electric bulb is represented as follows-

3. CONNECTING WIRES

Wires are made of metals that are good conductors of electricity, and can easily be stretched, a property known as ductility. Copper and Aluminum are ductile, good conductors, and economical to use for this purpose. Electrical wires are insulated with rubber-like polymers or PVC (polyvinyl chloride). Insulators prevent leakage of electric current to neighboring conductors and preserve the wires inside from environmental threats like water and heat. If there is a gap in the wires, the circuit is said to be incomplete and the device connected to it will not work like the bulb in the picture below. They are represented by straight lines in a circuit diagram.

 

Besides, these three components, circuits may have a switch and a resistor.

4. SWITCH

It is an electrical component that can connect or disconnect the path in an electrical circuit. The electric current stops flowing when the path is disconnected or the switch is off. The electric current continues to flow when the switch is in on position. A switch enables us to disconnect a device or an appliance when it is not in use. Hence, it helps us save electricity.

5 . RESISTOR

It is an electrical component with two terminals that implements controlled resistance to the flow of electric current in a circuit by limiting it. It is made up of a mix of carbon and ceramic. It represented by zigzag lines.

Thus, in Science, instead of drawing wires, bulbs, and batteries, we draw their symbols to represent them.

Thus, the circuit on the left (a) can be represented as the one on the right (b) –

Types of Electrical Circuit

SERIES –

In a series circuit, the current flows through each part of the circuit. The devices are connected one after the other in the same path. For e.g. two or more bulbs connected one after the other. However, there is a disadvantage here. If one filament breaks in any bulb, the whole circuit is broken and none of the bulbs will glow. The advantage of a series circuit is that it requires fewer wires and is easier to make and repair.

PARALLEL –

In a parallel circuit, the current is divided into separate paths. Here the devices are connected in separate branches and each branch represents an individual circuit. The advantage here is that if any device is impaired, it doesn’t affect the other circuits. These circuits need more wires and are complex to make and repair.

The wiring in our homes is done in parallel circuits so that failure in one device does not affect the functioning of the rest.

Check Point

  1. An electric cell has two terminals that are known as _______ and ________ terminal.
  2. The part of an electric bulb that glows is called the ________.
  3. The wires are made up of conductors and their covers are made with ___________ to protect us from getting electric shocks.
  4. A switch in off position is represented by the symbol ______________.
  5. An electric bulb or a lamp is represented by _________.
  6. The wiring in our homes is generally made using _________ circuits.

Answer Key

  1. positive and negative
  2. filament
  3. insulators
  4. parallel