Electricity, voltage, current and Resistance

Electricity, this is the first thing to study in electrical or electronics study. Electricity. When beginning to explore the world of electricity and electronics, it is important to start by understanding the basics of electricity and its related terms which voltage are, current, and resistance. These are the three basic building blocks required to utilize electricity. At first, these concepts can be difficult to understand because we cannot “see” them. One cannot see any electrical parameters with the naked eye. We cant see energy flowing through a wire or the voltage of a battery sitting on a table. In order to detect this energy transfer, we must use measurement tools such as multimeters to know what is happening with the electricity in a system. However, this tutorial will give you the basic understanding of voltage, current, and resistance and how the three relate to each other.

What is Electricity?

Electricity is all around us. We use electricity to give powerto our TV’s, computers, lights, mobile phones, refrigerators and oven and everything at our home. It’s not possible to imagine our day to day life without electricity, especially when power fails for some minutes or few hours, we get panic because it seems the world has stopped when electric power is not available at home. But what exactly is electricity? This is a very complicated question;in simplest words, electricity, is the form of energy which can be flown through the electronics present in an atom

In this tutorial we’ll focus on current electricity, it is the thing that powers our electronic equipments. Our goal is to understand how electricity flows from a power source through wires, lighting up LEDs, spinning motors, and powering our household devices.

Current electricity is the form of electricity which makes all of our electronic and electric devices work. This form of electricity exists when charges are able to constantly flow. As opposed to static electricity where charges gather and remain at rest, current electricity is dynamic; charges are always moving.

The definition of electricity is the flow of charge. Usually our charges will be carried by free-flowing electrons present in an atom. Negatively-charged electrons are loosely held to atoms of conductive materials. With a little push we can free electrons from atoms and get them to flow in a generally uniform direction.A closed circuit of conductive material provides a path for electrons to continuously flow.We need a source of electric potential (voltage), which pushes electrons from a point of low potential energy to higher potential energy.


The most common terms we discuss in studying electricity is voltage. A voltage is the difference in potential between two points in an electric field. Voltage gives us an idea of just how much pushing force an electric field has compared to the other point where there is no electric potential. We define voltage as the amount of potential energy between two points on a circuit. One point has more charge than another. This difference in charge between the two points is called voltage. It is measured in volts, which, technically, is the potential energy difference between two points. The unit of measuring voltage is VOLTS. Voltage between two points can be measured with an instrument called Voltmeter, or you can also use the voltmeter mode available in Multi meters. To know more about multi meters, click here


When there is a potential difference between two points in an electric field, if some path is available for electric energy to flow from higher potential point to the lower potential point, then electric energy flows through this through the available electronics in the conductor, this flow of electrons is called as Current, or electric current. The unit of measuring current is AMPERE. Currents in circuit can be measured using an instrument called Ammeter or ammeter mode in multi meter. To know more about multi meters, click here


When there is a potential difference between two points, and some path is available for electric energy to flow from higher potential to the lower potential, this path, from which current has to be flown always shows some oppose to the current flow, this is called as Resistance. Even good conductor like copper has some very little resistance associated with it, and resistance increases as the length of conductor increases. Due to this resistance offered to electricity, various interesting effects can be seen, and hence, there are some resistance offering component specially made for specific resistance values, these are called as RESISTORS. Resistance is always measured in Ohms (symbol Ω )Read More about resistors here.

Resistance is given by a simple formula

R = V / I


When describing voltage, current, and resistance, a common example is a water tank. In this example, charge is represented by the water amount, voltage is represented by the water pressure, and current is represented by the water flow. So for this example, remember

    Water = Charge

    Pressure = Voltage

    Flow = Current

The pressure at the end of this pipe can represent voltage. The water in the tank represents charge. The more water in the tank, the higher the charge, the more pressure is measured at the end of the pipe so more is the voltage.

We can think of this tank as a battery, a place where we store a certain amount of energy and then release it. If we drain our tank a certain amount, the pressure created at the end of the pipe goes down. We can think of this as decreasing voltage, like when we play games in mobile for long time, the batterygets low and eventually, phone turns off. There is also a decrease in the amount of water that will flow through the hose. Less pressure means less water is flowing. Here the flow means our current.

Now if the water flows through this pipe ending to some place down there, we say current is flowing and if it continues to flow forever, there will once come a point when the water in the tanks is over and nothing will flow from the pipe (remember the case when phone battery gets, down, tanks is empty and no current is flowing so our phone is Dead!!!)

Now imagine below

As shown in above figure, the size of the pipe is the total resistance offered to the water flow. If the pipe is larger, it means it will not resist the water flow means less resistance. And if the pipe is narrow, the water flow will be less. This is exactly similar to the resistance. If resistance is Less, more current flows in circuit and if resistance is More, less current flows in circuit.

Alternating Current and Direct Current

Note that these are the basics of how current electricity flows, but have you seen this?

What is this? A simple 3 pin socket that we see in our homes. Right?

This is the socket of the electric power that comes to our home from the mains line. This is a

  • 230 Volt
  • 50 Hz
  • AC Supply

Confused? Let’s see each concept one by one

AC stands for Alternating Current. The supply which comes to our homes through the main line is always AC supply, by the name it means that the polarity (yes, positive and negative) of this supply is continuously changing as time changes and its voltage is 230v. DC supply as compared to AC is the one in which the voltage value never changes and remains constant at a fixed voltage. The cells that we use in Remote Controls or in the wall clocks provide a constant DC voltage, to simply visualize this thing look at the below figure

Here the green line shows how the AC is alternating above and below the reference line, where as DC is a straight line providing a very constant voltage continuously.

The reason for having AC in our house hold supply is very simple. At those times, DC voltages were not that popular and almost all the devices were using AC very effectively to carry out their work, for example the Lamps, Tube light etc… so it was standardized that the supply provided will be AC and if DC is required, it will be taken from suitable DC power Sources. Next we’ll see what are DC power sources available to power our small electronic circuits

How LDR Works (Light Dependent Resistor)

How LDR Works (Light Dependent Resistor)

This tutorial is about understanding how LDR Works. A Light Dependent Resistor (LDR) is also called a photo resistor or a cadmium sulfide (CdS) cell. It is also called a photoconductor. It is basically a photocell that works on the principle of photoconductivity. The passive component is basically a resistor whose resistance value decreases when the intensity of light decreases.

The resistor behaves as per amount of light and its output directly varies with it. In general, LDR resistance is minimum (ideally zero) when it receives maximum amount of light and goes to maximum (ideally infinite) when there is no light falling on it. The resistance is very high in darkness, almost high as 1MΩ but when there is light that falls on the LDR, the resistance is falling down to a few KΩ (depending on the model.

 Light dependent resistors come in different shapes and colors. LDRs are very useful in many electronic circuits, especially in alarms, switching devices, clocks, street lights and more. There are some audio application uses such as audio limiters or compressors. It is used to turn ON or OFF a device according to the ambient light.

 The vast majority of LDRs are made from cadmium-sulphide (CdS), and they are very cheap, but also not very accurate. They are very good for detecting changes in light levels and determining if it is ‘dark’ or ‘light’, but without individual calibration they not suitable for accurately measuring light levels.

How Does a CdS Photocell Work

 Pictured below is a typical light dependent resistor. It has two wire leads which terminate in the face of the light detector – the two metal dots you see are the ends of those electrodes. The main body of the light detector component is made of ceramic – an excellent insulator. On the face of the ceramic a thin strip of cadmium sulphide is coated in a zig-zag pattern (to maximise the length of the strip while keeping the component small) which is connected at each end to an electrode. The front face is then coated in clear plastic, epoxy, glass, or similar.

how ldr works

How LDR works

Cadmium-sulphide is a high resistance semiconductor, and is chosen for light detectors as it gives the same spectral response as the human eye – i.e. it ‘sees’/responds to the same range of wavelengths of light that we can see. Specifically, cadmium-sulphide is a photoconductive material. That means that photons of light hitting it with sufficient energy will release electrons from their atomic bonds.

When a negatively charged electron is freed by a photon of light, it leaves behind a positively charged ‘hole’. When a voltage is applied across the two wire leads of the light detector, the free electron moves one way along the CdS strip, and the free ‘hole’ moves the other way; and it is this movement of charge which is electricity flowing through the light detector. The higher the light intensity, the more photons of light are hitting the CdS strip, the more electron-hole pairs are generated, the more electricity can flow through the light detector, and so the lower the resistance of the light detector (i.e. it is easier for electricity to flow through the light detector when the light intensity hitting it is high).

How LDR works

It is relatively easy to understand the basics of how an LDR works without delving into complicated explanations. It is first necessary to understand that an electrical current consists of the movement of electrons within a material. Good conductors have a large number of free electrons that can drift in a given direction under the action of a potential difference. Insulators with a high resistance have very few free electrons, and therefore it is hard to make the them move and hence a current to flow.

 An LDR or photo resistor is made using semiconductor material with a high resistance. It has a high resistance because there are very few electrons that are free and able to move – the vast majority of the electrons are locked into the crystal lattice and unable to move. Therefore in this state there is a high LDR resistance.

You need to take into considerations about the size of LDR because it’ll affect how its placed on PCB. The foot print of LDR are different based on size. In order to place LDR on PCB, the dimensions of LDR are important. If you don’t know about PCB Design, more about it can be read here

Now to answer the original question about how ldr works, here it is. As light falls on the semiconductor, the light photons are absorbed by the semiconductor lattice and some of their energy is transferred to the electrons. This gives some of them sufficient energy to break free from the crystal lattice so that they can then conduct electricity. This results in a lowering of the resistance of the semiconductor and hence the overall LDR resistance.The process is progressive, and as more light shines on the LDR semiconductor, so more electrons are released to conduct electricity and the resistance falls further.

I’ve tried to explain how ldr works in in the simplest language for complete beginners. If you want to deep dive into the technical details of LDR working, you can read so here and here you can see how to actually use it in a circuit



Buzzer, horn antenna with a similar function, namely, the energy conversion from the action, the speakers, the key device, which is the electrical energy to sound energy is fundamental to sound chamber Danshi subsidiary device determines its maximum output power and frequency response, then We discuss the sound system down is to get the most energy.

What is Buzzer?

A buzzer is a mechanical, electromechanical, magnetic, electromagnetic, electro-acoustic or piezoelectric audio signaling device. A piezo electric buzzer can be driven by an oscillating electronic circuit or other audio signal source. A click, beep or ring can indicate that a button has been pressed.

Types of Buzzers

There are several different kinds of buzzers. At Future Electronics, we stock many of the most common types categorized by Type, Sound Level, Frequency, Rated Voltage, Dimension, and Packaging Type. The parametric filters on our website can help refine your search results depending on the required specifications.

The most common sizes for Sound Level are 80 dB, 85 dB, 90 dB and 95 dB. We also carry buzzers with Sound Level up to 105 dB. There are several types available including Electro-Acoustic, Electromagnetic, Electromechanic, Magnetic and Piezo, among others.

Buzzers from Future Electronics

Future Electronics has a complete selection of buzzers from several manufacturers that can be used as an electromagnetic buzzer, piezo buzzer, electro-acoustic transducer, piezoelectric transducers or magnetic buzzer for any electric circuit applications. Simply choose from the buzzer technical attributes below and your search results will quickly be narrowed in order to match your specific buzzer application needs.

If you have a preferred brand, we deal with CUI Inc, Intervox/ICC, Mallory and Murata, among others. You can easily refine your buzzer product search results by clicking your preferred buzzer brand below from our list of manufacturers.

Applications for Buzzers:

Typical uses of buzzers include:

  • Alarm devices
  • Timers
  • Confirmation of user input (ex: mouse click or keystroke)
  • Electronic metronomes
  • Annunciator panels
  • Game shows
  • Sporting events
  • Household appliances

Piezo buzzer is the handy sound generator used in electronic circuits to give an audio indication.It is widely used as an alarm generator in electronic devices. It is available in various types and sizes to suit the requirements. A Piezo buzzer has a Piezo disc and an oscillator inside. When the buzzer is powered, the oscillator generates a frequency around 2-4 kHz and the Piezo element vibrates accordingly to produce the sound. An ordinary Piezo buzzer works between  3 – 12 volts DC.

Working of the Piezo element

The piezo element is a circular-shaped metal plate with a thin coating of Piezo material. The piezo material used is Lead Zirconate Titanate. This material exhibits both Direct and Indirect piezoelectric properties. Indirect piezoelectric property is the vibration of the piezoelectric crystals in the presence of an electric field. The piezoelectric crystals also show direct piezoelectric properties in which mechanical stress like vibration or application of heat generates around 1-2 volts in the Piezo element. The white Piezo material coating is Positive while the rim of the element is Negative.

Oscillator circuit inside the buzzer consists of an Inductor, a transistor, capacitors, and resistors. When the oscillator circuit gets 3-12 volt DC, The transistor, Inductor combination oscillates which are fed to the Piezo crystals and the crystals and the plate vibrate according to the frequency. In order to give resonance, the rim of the element is glued to a plastic case so that the plate can vibrate freely.

Why Piezo buzzer generates piercing sound?

The oscillation in the Piezo buzzer is between 2 – 4 kHz. This sound is piercing because our hearing threshold is maximum in this frequency. Buzzer uses this frequency to get easy attention even in a highly noisy environment. Buzzers are used as alarms so this frequency is necessary.

How to handle Piezo element?

Piezo element is prone to weather changes and aging. The piezoelectric property may deteriorate due to aging and the buzzer may fail to work. The Piezomaterial is coated as a thin film so that during soldering, the wire along with the piezomaterial may detach. Once a portion of the Piezo material is detached, that element cannot be used. So always use very thin wire and apply solder only once. Overheating may damage the piezo material. If it is stored, use a plastic cover and keep it in a place free from moisture and heat.

Direct Piezoelectric Effect

Mechanical vibration can generate electricity in Piezo element. Connect a high bright transparent LED directly on the Piezoelement with the correct polarity. Gently tap in the central white part of Piezo element. LED will blink.

Building an Electronic Circuit


In previous lessons, we have learned a lot of things regarding to Electronics, its components, Circuits and various platforms for circuit mounting. In this session we will learn the actual Circuit making using a very interesting plat form ‘Bread Board‘. The process is simple and easy to understand. We have to follow some steps to build perfect circuit. In this lesson we will build a basic circuit of led and resistor. We will turn ON led with the help of resistor and supply.

Circuit Diagram:

Circuit Diagram

Components  Required:

  • Light emitting diode = LED1
  • Resistor:R1=1 Kilo Ohm
  • Color Code for 1 K Ohm : Brown-Black-Red-Golden
  • Battery: 9 Volts
  • Bread Board

Step 1:

Take a bread board and start to mount component on it.

Bread Board

Step 2:

Connect resistor of 1 Kilo Ohm on breadboard as shown in below image.

Connecting a Resistor

Step 3:

Connect Led on the Bread board.

LED Connection

Step 4:

Connect Anode terminal of Led to one terminal of resistor and Cathode to Ground terminal.

Anode and Cathode Terminals

Blue wire is connected between Anode i.e positive terminal of Led and resistor. Black Wire is connected to Cathode i.e. Negative terminal of Led.

Step 5:

After completion of all  connections connect battery to the bread board Circuit. As shown in image insert positive and negative terminal correctly. Led will Glow after giving supply to it.

Battery Connection


Just like resistor, a capacitor is a 2 terminal electronic component with very interesting working nature. We all know in our life, there are few people (like our Parents, A good Friend, a cousin or sister) who is always our savior, who always protects us in need and gives us that important BOOST, sometimes, its financial Boost or sometimes, these people correct our mistakes. So are capacitors, in any electronic circuit, capacitors are used either to correct something wrong, or to give a boost. And by combining capacitors with other components, we can create some really good electronic effects.


Capacitors are special because they have ability to store energy. It just acts as a fully charged battery. You might have seen large capacitors which are also called as condenser in our domestic ceiling fans, as well as with the motor Pumps. In this tutorial, we’ll see what exactly capacitor is made up of, how it works and how to make good use of capacitors. We’ll also see various types of capacitors and know how to measure their capacity

How a capacitor is made

A capacitor is actually a sandwich of 2 Metal plates placed close to each other but not touching each others. It simple means exactly as shown in the below figure. Capacitors are exactly as shown below where there are 2 metal plates separated by some specific material called Di-electric. Now this dielectric is not any mystical component, it’s just simply any insulating material. Insulating material means the material which cannot conduct electricity, like paper, rubber, ceramic, plastic, or sometimes even pure air!!! So it’s anything that will not allow the flow of electric current.

The metal plates (brown ones in below figure) are made up of different conductive materials, which include most metals like aluminum, silver, tantalum or any other metal. These are connected to a metal wire which forms the lead of capacitors.

Cap Plates

So, as shown above, is the construction of capacitors. And because of this type of construction, the symbol of the capacitor is like this

Capacitor Symbol

So this is a generalized capacitor symbol showing two metal plates spaced apart not touching each other. There are other capacitors symbols also depending upon their nature of operation, but first we need to know how a capacitor at all works.

How Capacitor Work

Electric current is the flow of electric charge, which is what electrical components use to light up, or do whatever they do. When current flows into a capacitor, the charges get “stuck” on the plates because they can’t go beyond the insulating dielectric materials. Electrons which are negatively charged particles are saturated into one of the plates, and this plate becomes overall negatively charged. The large mass of negative charges on one plate pushes away like charges on the other plate, making it positively charged as shown below

Capacitor Electric Field

The positive and negative charges on each of these plates attract each other, because that’s what opposite charges do. But, with the dielectric sitting between them, as much as they want to come together, the charges will forever be stuck on the plate (until they have somewhere else to go).

The stationary charges on these plates create an electric field, which influence electric potential energy and voltage. When charges group together on a capacitor like this, the cap is storing electric energy just as a battery might store chemical energy. When such situation occurs, we can call that this capacitor is CHARGED.

Now this charged capacitor acts like a battery (bigger the capacitor, more the charges stored in it) if we provide some conducting path for this charge to flow, the charges stored in capacitor will quickly discharge providing a momentary current, which acts as required little boost in many circuits. If we connect a resistor in series with capacitor, it creates more interesting things, first, it charges slowly and then it discharges slowly too, this is the timing effect which is used to build hundreds of different things

Unit of Capacitance and Polarity

Depending upon how the capacity of capacitors, there are various capacitor types

The capacity is measured in unit Called Farad

One farad is defined as the capacitance of a capacitor across which, when charged with one coulomb of electricity, there is a potential difference of one volt. Conversely, it is the capacitance which, when charged to a potential difference of one volt, carries a charge of one coulomb. Plainly speaking 1 Farad is too much of capacitance, even 0.0001 Farad (1 mili farad) is also a very big capacitor. Usually we see capacitors rated in the Pico (10-12 ) to microfarad (10-6 ) range. As a thumb rule, capacitors having capacitance greater than 1 microFarad are polarized capacitors. It means that the have specific direction in which they should be connected in a circuit (positive terminal and negative terminal) see below picture for polarized capacitor and non polarized capacitor

Polarized Capacitors

Types of Capacitors

Depending upon the capacity of capacitor and the electrolytic material used in between capacitor plates, there are different types of capacitors. Here are few with Pictures and their names. The name of capacitor itself suggests which di-electric Material is used

Ceramic Capacitors

Ceramic Capacitor

Ceramic capacitor: The ceramic capacitor is a type of capacitor that is used in many applications. Values of ceramic caps range from a few picofarads to around 0.1 microfarads. Ceramic capacitor types are by far the most commonly used type of capacitor being cheap and reliable. In view of their constructional properties, these capacitors are made up of ceramic material

Electrolytic Capacitors

Electrolytic capacitor

Electrolytic capacitor:   Electrolytic capacitors are a type of capacitor that is having a fixed polarity. They are able to offer high capacitance values – typically above 1μF, and are most widely used for low frequency applications – power supplies, decoupling and audio coupling applications as they have a frequency limit if around 100 kHz.

Tantalum Capacitors

Tantalum Capacitor

Tantalum capacitor:   Like electrolytic capacitors, tantalum capacitors are also polarized and offer a very high capacitance level compared to size. However this type of capacitor is very intolerant of being reversely polarized. It often explodes when connected in reverse direction.

Silver Mica Capacitors

Silver Lead Capacitor

Silver Mica Capacitor:   Silver mica capacitors are not as widely used these days, but they still offer very high levels of stability, low loss and accuracy where space is not an issue. They are primarily used for Radio Frequency applications and they are limited to maximum values of 1000 pF or so

Polystyrene Film Capacitors

Polystyrene Capacitors

Polystyrene Film Capacitor:   Polystyrene capacitors are a relatively cheap form of capacitor but it offers not so exact value of capacitance. They are tubular in shape resulting from the fact that the plate / dielectric sandwich is rolled together, but this adds little inductance limiting their frequency response to a few hundred kHz. They are generally only available as leaded electronics components (Not available in Surface mount type L)

Ceramic Capacitors

Polyster Film Capacitor

Polyester Film Capacitor:   Polyester film capacitors are used where cost is a consideration as they do not offer a high tolerance. Many polyester film capacitors have a tolerance of 5% or 10%, which is adequate for many applications. They are generally only available as leaded electronics components.

Metalized Polyester Film Capacitors

Metalized Polyester Film Capacitor:

Metalized Polyester Film Capacitor:   This type of capacitor is essentially a form of polyester film capacitor where the polyester films themselves are metalized. The advantage of using this process is that because their electrodes are thin, the overall capacitor can be contained within a relatively small package.

Polycarbonate Capacitors

Poly-carbonate Capacitor

Polycarbonate capacitor:   The polycarbonate capacitors have been used in applications where reliability and performance are critical. The polycarbonate film is very stable and enables high tolerance capacitors to be made which will hold their capacitance value over time. 

Polypropylene Capacitors

Polypropylene Capacitors

Polypropylene Capacitor:   The polypropylene capacitor is sometimes used when a higher tolerance type of capacitor is necessary than polyester capacitors offer. As the name implies, this capacitor uses a polypropylene film for the dielectric. One of the advantages of the capacitor is that there is very little change of capacitance with time and voltage applied.

Glass Capacitors

Glass Capacitors

Glass capacitors:   As the name implies, this capacitor type uses glass as the dielectric. Although expensive, these capacitors offer very high levels or performance in terms of extremely low loss.

Super Capacitors

Super Capacitor

Supercapacitor:   Also known as a supercapacitor or ultracapacitor, as the name implies these capacitors have very large values of capacitance, of up to several thousand Farads. They find uses for providing a memory supply and also within automotive applications.