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Electric Circuits

Exotic view of a city Exotic view of a city Electrical circuits play a major role in making a city colourful. Life without these circuits is unimaginable! Lets learn more of these electrical circuits in details as we unwrap this topic.

Learning objectives

After completing the topic, the student will be able to:

  • Understand the working of an electrical circuit with importance to various types of sources of emf and their working.
  • Distinguish between primary and secondary voltage sources and discuss the importance of internal resistance.
  • Discuss and explore about the concept of voltage and currents and analyze different types of moving coil galvanometers.
  • Explore different types of electrical circuits with series and parallel combination of resistances.
  • Understand how electrical energy flows in a circuit based on the analogy of water flowing in a closed pipe.
  • Differentiate between alternating and direct currents and explore AC to DC converters.
  • Determine energy and power in any electrical circuit, where the energy is either delivered or extracted.
  • Observe that electricity is present in the human body and its importance of how the information through nerve cells is transmitted to the brain.
Symbols for electrical components
Symbols for electrical components In electric circuits, we have to show various electrical components such as cell, a battery, connecting wires, fixed resistance, resistance, ammeter, voltmeter, galvanometer, switch, etc. The common electrical symbols for electrical components which are used in drawing circuit diagrams are given in the above table.
Components in a circuit

A cell or battery can make electrons move and electric current flow. But there must be a conducting path such as wires or bulb between the two terminals of the cell through which electrons can move causing the electric current to flow.

A circuit is a continuous conducting path consisting of wires, other resistances (like electric bulb etc) and a switch, between the two terminals of a cell or battery along which an electric current flows.

The adjacent figure shows a cell with a positive terminal and negative terminal. The positive terminal of the cell is connected to one end of the bulb holder with a copper wire (called connecting wire) through a switch. The negative terminal of the cell is connected to the other end of bulb holder. If the switch is closed, then the circuit is complete. Hence a current flows in the circuit and lights up the bulb. If the switch is open, then there is a break in the circuit. Hence no current flows through the bulb and the bulb stops glowing.

Series and Parallel circuits Series and Parallel circuits - examples (A) Series circuit: Christmas lights are wired in series. If you pull out one of the light bulbs from a strand, the rest of the lights will 'switch of'.
(B) Parallel circuit: This is how our homes are wired. Each room has it's own parallel lighting circuit. So, even if one light bulb is pulled out, the other light bulbs stay lit.
Series and parallel connections

Circuits consisting of just one battery and one load resistance are very simple to analyze, but they are not often found in practical applications. Usually, we find circuits where more than two components are connected together. There are two basic ways in which to connect more than two circuit components: series and parallel.

Suppose there are three light bulbs to be connected in a circuit. In a series circuit, the light bulbs are arranged in a chain, so the current has only one path to take. Light bulbs can be added to the same chain, with no branching point. As more and more light bulbs are added, the brightness of each bulb gradually decreases. This observation is an indicator that the current within the circuit is decreasing. If one of three bulbs in a series circuit is unscrewed from its socket, then the other bulbs will not glow.

In a parallel circuit, the light bulbs are connected in two or more paths, so the current is divided into two or more paths to complete the circuit. For parallel circuits, as the number of light bulbs increases, the overall current also increases. This increase in current is consistent with a decrease in overall resistance. If an individual bulb in a parallel branch is unscrewed from its socket, then there is still current in the overall circuit in the other branches and the remaining bulbs will still glow.

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