• Introduction
• Glossary of Terms
  • Power and Ground
  • Conductor and Resistor
  • Electrical Characteristics of a circuit:
  • Ohm’s Law explained: Water Analogy
  • Electric Current Flow
  • Alternating Current and Direct Current
  • Series and Parallel Connection
  • Short Circuit
• Components of Electric Circuits
  • Switches
  • Resistors
  • Capacitors
  • Diodes and LED's
  • Transistors and Relays
  • Multimeter
• Presentation

Energy¹⁾ is defined in Wiki as, „In Physics, energy is a property of objects, transferable among them via fundamental interactions, which can be converted in form but not created or destroyed“. In other words, the Law of Conservation of Energy states that „The total amount of energy in an isolated system remains constant.“ A consequence of this law is that energy cannot be created nor destroyed. When energy is changed from one form to another, we call it Transduction. It can be from Physical to electrical (say, a dynamo), or electrical to physical (an electric motor) or even chemical to electrical just like in the case of a battery.

A computer by its own do not sense any these energy forms, nor does its little electrical output directly control any system which are non-electrical in nature.This can be explained with a small ‘Speech Recording’ to a digital file on to a Computer. A computer cannot take input as sound as it is. But it can accept electrical energy, as pulses. So, a Transducer (Microphone) is used here, to convert, sound energy (vibrations) to equivalent electrical pulses. The computer can store this as magnetic pulses, on the hard disk as magnetic pulses. So, in general, Transduction is just the process of changing one form of energy to another.

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An electric current is simply the flow of electrons from one point to another. Like all other forms of energy, electrical energy too flows from a region of higher energy or Power(positive terminal in the case of a battery) to a lower(negative terminal or ground in the case of a battery) region of energy.

The medium through which electricity flows from the higher energy point or terminal to the lower energy point is called a Conductor. Objects differ in their ability to conduct. Electrons can travel faster through metals, so an metal wire is mostly chosen as a conductor. Even air conducts electrons. But the ability of air to conduct electricity is less than metal. So we can call metal more conductive than air. Or in other words Conductivity of metal is more than that of air. This can be put in the other way round too. When an object tries to oppose the flow of electrons, that object is said to have Resistance. Like conductivity, resistivity of objects differ from one another. Plastic is almost 100% resistant to electricity i.e., it doesn't allow electrons (electricity) to pass through them. But at the same time a metal wire almost not at all resistant to electricity. The resistance property of substances can be used in an electrical circuit for purpose of transduction. Objects which resist electricity(if they are not 100 percent resistant), can be used as a transducer. Tungsten filament in the electric bulbs is a resistor, which allows only very less amount of energy to pass through. Energy cannot be created nor destroyed. So, here the rest of the electric energy is converted into light energy. In the same way, the coil in the iron box, or heater converts electrical energy to heat. In a loudspeaker electrical energy is transduced to physical vibrations.The object which transduces the energy here can also be called as a load. An electric circuit can simply called as a closed loop which is having the electricity source and load.

There is always a threshold level of electricity that should pass through with resistor to transduce the energy to another form. For example if the amount of electricity passing through an electric bulb, is not enough, it would not light up. Also, there is a maximum level of electricity that every electrical device can tolerate, beyond which the bulb filament in this case would melt and break, breaking the circuit. For our convenience, we normally add a switch, to break and resume a circuit. Any device which can stop and resume the flow of electrons this way can be called as a switch. Here's an animation on how a light switch works.How a Light Switch Works

Let us see some basic electrical characteristics. In every electrical circuit:

• Voltage is the amount of relative level of electrical energy between two points in the circuit. This is measured in Volts.
• Current is the amount of electrical energy passing through a point. Its measured in Amperes.
• Resistance of a component, is said to be the amount the component resists to the flow of current through it. Its measured in ohms.
• Power is the amount of energy used up in a circuit. It is always product of Current and Voltage. Its measured in Watts. Or Watts = Voltage X Ampere.
• Ohm’s Law : Voltage = Current X Resistance..

Ohm's Law stated above can be better explained with an example. Consider a limited supply of water flowing through a hose. Consider the water flow similar to electron flow, where the amount of water flow is Current in the case of electricity, and speed of the water as Voltage. When the diameter of the hose is more, the water has enough space to flow. Now when the diameter is less, the Resistance is more, so water has to flow faster. The above example shows how voltage increases with resistance. When we look at the current flow. We can also see that when resistance goes up, current flow decreases. Here's a nice animation that describes the Water Analogy:Animation: Water as an Analogy for Electric Current and a video explaining the same: Introduction to Circuit Analysis - Water Analogy

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Consider current flowing in an electric circuit as water flowing in a river. The voltage is like slope that provides the potential energy that lets the water flow. Higher the slope there will be more energy to move water.

• High Voltage,High Current: This can be compared to Niagara Falls: There is lots of water and lots of energy is being dissipated. Example:- High-tension, high-voltage power transmission line.
• High Voltage,Low Current: This can be compared to Angel Falls in the dry season. Here the water is falling from a huge height (lots of voltage), but there isn’t much of it (low current). Example:- Static Electricity.
• Low Voltage, High Current: This can be compared to the Mississippi river with lots of water, but it moves very slowly. Nevertheless, there’s lots of energy in that system. Example:- Graphics chip by NVIDIA or ATI. Their high-end chips consume 200-300watts, but with a power supply of around 1v. That implies 200-300 amps of current (at low voltage) going into those chips!
• Low Voltage, Low Current: This can be compared like a small creek that doesn’t do major work, but has just the right amount of energy to make a pleasant babbling sound. Example:- Embedded systems like mobile phone which consumes tiny current(milliamperes or mA) at low voltages ( 1v). It still does a lot of stuff, but tries to consume as little power as possible while doing it.

When there is a difference between the level of electrical energy between two points in a circuit, electricity always flows from the higher energy region to the lower energy region. Also, its a fact, in a closed circuit, all electricity in a circuit will be used up. This means it can either flow from the positive to the negative terminal, or can be used up in the transduction process, say like resistor changes the electrical energy to heat.

There are generally two types of current supply - Alternating Current(AC) and Direct Current(DC). If a source gives current on the main wire, and ground and the voltage between them stays stable, its normally called as DC or Direct current. If the source alternates the voltage on two wires, its called AC or Alternating current.

When more than one component is used in a circuit, there are different strategies of connecting them up between two terminals of a battery to give different results.

1. Series connection: Consider two bulbs in a circuit, a smaller bulb and a larger bulb between positive and negative terminals of a battery. If the components (bulbs in this case) are connected in a chain, as the current first flow from positive terminal, enters the first small bulb and goes out to the larger and then to the negative terminal. In this connection all components are on the same electrical path. Here the current is same in all components. The voltage drops as components increases in this case.
2. Parallel Connection: Consider the smaller and larger bulb connected to the same positive and negative terminals of the battery.In this case, we have two paths, with different resistances. The smaller path offers a smaller resistance, and the larger one offers more resistance. The smaller resistance will have more current pass through it. The voltage across the circuit will be same in this case.

Here's a video from MIT showing the Series and Parallel Circuits using Water Analogy: Series and Parallel Circuits: A Water Analogy

In the circuit on the right side, all the components are connected in parallel. There is a wire connected in parallel to the two bulbs. The current in a circuit follows the path of least resistance. Since the wire has almost no resistance, almost all of the current goes through it. From the wire, the current goes right back to the battery, heating it up and eventually blowing it up. This is called a short circuit. This generally happens when there is not enough resistance for the load in the circuit.

The following section describes the components that we generally use in most of the electric circuits.

Schematic symbol:

Switches are parts of circuit, which are used to control the flow of electricity between two points when introduced between them. Switches can be of different types: Toggle and Momentory Switches

• Toggle switches: They do not have a default position. For instance, the lamp switch in houses, which stays in on or off position according to the use.
• Momentory switch: The keyboard switch of a computer, which goes back to the default off position breaking the circuit, once released.

Switches can be also classified as Normally Open or Normally Closed based on their activity on the circuit.

• Normally Open: They dont conduct electricity all the time, and on activation they conduct electricity.
• Normally Closed: They conduct electricity when they are not activated.

Switches will have voltage rating for them. That means the maximum tolerable voltage it can handle beyond which its function fails.

Schematic Symbol:

Fixed Resistor:

Variable Resistor:

Resistors offer resistance to the flow of current flow through them. When the resistance is more the current flow through them reduces and vice versa. Resistor’s resistance is measured in ohms. Resistors normally convert the current to heat, when they pass the current through them. Film resistors and carbon resistors are the most common type of resistors.
When resistors are connected in parallel, the total resistance is decreased whereas when they are connected in series, the total equivalent resistance is equal to the sum of the individual resistances.The value of resistance of a resistor is marked with a number of coloured bands. Each colour stands for a number. Three colour bands shows the resistors value in ohms and the fourth shows tolerance. Resistors can never be made to a precise value and the tolerance band (the fourth band) tells us, using a percentage, how close the resistor is to its coded value.⁴⁾
Resistors can be fixed value resistors or variable resistors. When the resistance across two points in the circuit has to be constant, normal fixed resistors can be used. For example if we want to connect a LED bulb to the power supply 220V, we do not need a variable resistor to be connected a resistor in series. But if we want a dim and brighten adjustment for a light to the power supply, we can use a variable resistor in series with the bulb. Examples: Potentiometer, thermistors, photoresistors etc. Resistors gives a detailed description on Resistors and their colour coding schemes.

Schematic Symbol:

Wiki says „A capacitor is a passive two-terminal electrical component used to store energy electrostatically in an electric field.“⁵⁾. In an electronic circuit capacitor can be used like a buffer device. It can store and release electrical energy. The ability of a capacitor the store and release energy is defined by its Capacitance. This is expressed in Farads. A farad is large capacitance quantity, so normal capacitors are rated in nano or pico farads. A capacitor is generally used for the electronic flow conditioning i.e., when there is dip in the flow, a capacitor can provide the extra power from its buffer, and when there is a spike it can store those excess energy. This leaves a conditioned electrical signal to the output. Introduction to Capacitors tutorial gives an in-depth view of the Capacitors.Capacitors page contains another good illustration of the principles and working of a capacitor.

Schematic Symbols

Diode:

LED:

Diodes are those electronic components which would allow only electricity to flow through them in one direction. Every diode with have a cathode (-) and an anode (+) . The most common kind of diode is the semiconductor diode.Introduction: Diodes and Rectifiers is a good article about the diodes and rectifiers. To know more about diodes, check p-n Junction Diode video which describes the working of a p-n junction diode in detail.
A practical application of diode is to covert AC (which has two direction) to one direction DC. Light Emitting Diodes(LED): Light emitting Diode is a kind of diode which emits light from the junction of cathode and anode when electricity passes through them. They are used widely in almost all the walks of daily life. For instance, they form numbers on digital clocks, transmit information from remote controls, light up watches and tell you when your appliances are turned on etc.⁶⁾MAKE presents: The LED shows a good demonstration on LED's, who invented it, how to use it, and how to make your own etc.Light Emitting Diode (LED) is another interesting video about LED's.

Schematic Symbols:

Transistors:

Relays:

Transistors and Relays act like electronic switches. When a small current is passed through a transistors ‘base’ lead, if it passes a certain threshold level, it opens a bigger switch between other two leads of them. Transistors are of two main types - NPN and PNP. Generally most of the transistors are NPN transistors. Every transistor has a base, collector and an emitter. Transistors are generally used as amplifiers.Because a transistor's collector current is proportionally limited by its base current, it can be used as a sort of current-controlled switch. A relatively small flow of electrons sent through the base of the transistor has the ability to exert control over a much larger flow of electrons through the collector.⁷⁾ Transistor shows the simple use of a transistor.
Same happens with a relay too, a relay can be triggered with a 5V supply, but may open or close a larger circuit which may set out a flow of electronic flow which may be several folds bigger than that.

A multimeter is a device which can be used for applications like measuring characteristics of various components such as resistance or capacitance. Its also a handy tool, for checking the Voltage or Current between two different points of the circuit. Multimeters have their own tolerance and accuracy levels. Multimeters differ from one another based on their capacity to measure each of the characteristics.

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