Electronics FAQ – Your Multilingual Guide to Electronics

Can the Energy Stored in an Inductor Be Used Practically? Applications, Benefits, and Real-World Examples. Why does an inductive load create sparking across contacts?  An inductor stores energy in the form of a magnetic field as long as current is flowing through it. As the current stops, the magnetic field began to collapse. Collapsing magnetic flux is also a rate of change of magnetic flux that will induce a large voltage spike (back EMF) across it. Energy stored in an Inductor:  Since this induced voltage is parallel to the inductor coil, it decays by converting it to heat across the coil resistance. In that process, the coil generates a magnetic field again due to the flow of decaying current through the coils, which results in electromagnetic interference in the radio operation and sparking across open contacts. Adverse effects of stored energy in an inductor:  Can we put this back-EMF into use? Yes. Practical Use of Stored Energy in an Inductor:  Spark-ignition...

How Long Can a 9V Battery Power an LED using a 4.5K current-limiting resistor? Calculations and Practical Tips A good quality alkaline 9V battery pack has an AH capacity of 500 mAH. Calculation:  Assuming a drop of 2V across the LED, the current drawn by the battery for the LED circuit would be 7V/4.5K 1.5 mA So LED will be ON for 500/1.5 = 333 Hrs. Conclusion:  An LED will stay lit for 333 hours or approximately 14 days.  FAQ Set: Q1: How long can a 9V battery power an LED? The runtime depends on the battery capacity, LED current, and any series resistor used. It can be estimated using   battery capacity/circuit current . Q2: How do you estimate the battery life? Battery life (hours) ≈ Battery capacity (mAh) / Load current (mA). Example: A 9V alkaline battery (~500 mAh): Battery life ≈ 500 1.56 ≈ 320  hours Battery  life ≈ 1.56 500 ​ ≈ 320  hours Q3: What factors affect battery life in this circuit? Actual battery capacity LED forward voltage var...

Electrical Earthing Tests – Importance, Types, Procedures, Safety Standards, and Best Practices Explained. Easy method to test home earthing. An instrument that measures ground (earth) resistance: If you're paranoid about the effectiveness of the earthing, then you need three three-wire earthing tester. There is a procedure for that. You may also call a third-party agency that certifies electrical earthing. But, is there an easy, inexpensive method? Yes. It is crude, but it gets the job done. Method-1 (Using filament lamp) Take a 100W filament bulb with a holder. First test it across the phase and neutral of the home electrical plug. Note the brightness. Then connect the bulb to the Earth and the Phase of the plug. Note the brightness. If the electrical earthing is good, you will have equal brightness in both cases. Why bulb lights with Earth-Phase connection? I have explained it   here. Method-2 (Using Digital Multimeter) You need a DMM.   Measure the voltage difference betwe...

How Does a Capacitor Reduce Ripple in DC? Working Principle, Smoothing Effect, and Applications. Why is it important in AC to DC conversion?  Filtwer capacitor analogy with a water tank: Suppose your home has intermittent water supply problems. When you need water, the supply is not sufficient. When you don’t need water, you don’t know what to do about the excess water. What is the solution to this problem? Have a water storage tank, don’t you? Similarly, unfiltered, raw rectified DC voltage is not as smooth as battery voltage. Unfiltered DC voltage:  As shown above, sometimes it is zero, sometimes it is maximum. It is always varying with respect to time. But electronic devices require a smooth DC voltage, as shown below. DC voltage of Battery:  The solution is to incorporate an electronic reservoir called a capacitor . AC to DC conversion using a diode and a capacitor:  Filtered DC voltage ripple waveform: It stores excess electricity and releases it to the load whe...

Why Doesn’t a Transformer Amplify an Audio Signal? Working Principle, Limitations, and Practical Applications. Why is impedance matching important?  Amplification means the product of voltage and current: When you use the word ‘Amplify in Audio’, it means power amplification. Power is the product of voltage and current. The transformer will amplify the voltage, but what about current? A transformer is a constant power device. The ‘output power’ is slightly less than the ‘input power' due to transformer losses. So, if it amplifies voltage, it has to reduce current to conserve power. Hence, as there is no difference between input and output power, on the contrary, output power is slightly less than input power, the audio signal gets attenuated due to losses in the transformer. Hence, no transformer can amplify an audio signal. To amplify an audio signal, we need to amplify voltage as well as current. This job is undertaken by a powered audio amplifier. Transformer as impedance matchi...

Why Are Capacitors Used in Speakers? Role in Audio speaker systems, Crossover Networks, Sound Quality Enhancement and distortion reduction.  A single speaker is unable to reproduce the entire audio range faithfully. Hence, not only capacitors, but also air-core inductors and resistors, are used to split the entire audio range into two or three components and assign them to the specific speaker that best represents it. Typical crossover circuit: A crossover circuit assembled PCB:  That said, designing a crossover is not a simple task. It needs extensive computer model simulation and several practical trials to match it to the speaker drivers, so that audio reproduction is seamless without any breaks. FAQ Set Q1: Why are capacitors used in speakers? Capacitors are used to   control the flow of high and low-frequency signals , directing them to the appropriate speaker drivers and improving overall sound quality. Q2: What is the role of capacitors in crossover networks? In cr...

Why Does AC Current Reverse Direction Periodically? Understanding Alternating Current generation, Frequency, and Working Principle of an AC generator The answer to this question goes back to the generator where AC power is generated. A simple voltage generator:  Imagine a simple loop of coil is rotating between the two strong magnetic bars. 0 to 180 degrees,i.e. Half rotation. You will notice that when the coil is perpendicular to the magnetic field, its output is minimum or zero due to the minimum linkage of the magnetic field. But as the coil rotates to become parallel to the magnetic field, its output increases and becomes maximum when it is parallel. 180 to 360 degrees, i.e. Full rotation. The same cycle repeats, but now the voltage is negative. The following diagram explains it. Hence, as the AC voltage reverses its polarity periodically, the load current will also change direction of flow periodically. AC current direction: FAQ Set: Q1: Why does AC current reverse direction p...

Importance of correct Working Voltage for a Relay – Why it affects Function and Safety?  Relay various parts and their functions. Relay animation.  Let's see how relay functions: Parts of a typical relay: As you can see from the above animation, the coil must develop sufficient magnetic strength to overcome the spring tension of the armature that operates the contacts. At 12V, the coil may not develop that magnetic strength. Relay might operate, but not reliably. Also, weak spring relay contact pressure may lead to sparking and could damage it. FAQ Set: Q1: Why is the correct working voltage important for a relay? The relay’s coil is designed for a specific voltage. Applying   too low a voltage   may prevent it from activating, while   too high a voltage   can overheat or damage the coil, affecting both function and safety. Q2: How does incorrect voltage affect relay operation? Low voltage:   Coil may not generate enough magnetic force to close contact...

Why Is Transformer Rating Given in VA? Understanding Power in Volt-Ampere versus watts, Power Factor, and Transformer Efficiency related to inductive load Because the manufacturer of the transformer never knows where it is going to be used. Suppose if a transformer of 100KVA feeds a resistive load; it will develop 100 kilowatts of power across the load because the power factor of the resistive load is unity. If the same transformer feeds an inductive load of power factor 0.5, then it will develop only 50 kilowatts of power across the load. Hence, if I want to rate a transformer in watts, then I need to know the power factor of the load, which is impossible. So, the transformer is rated in VA, KVA or MVA. A mug of beer analogy of Power Factor: FAQ Set: Q1: Why is transformer rating given in VA instead of watts? Transformer ratings are given in   VA (volt-amperes)   because transformers must handle   apparent power , which includes both real power (watts) and reactive power...

Why Is Speaker Polarity Important? Correct Wiring, Phase Alignment, and Sound Quality Explained. Constructive and destructive sound interference explained.  Speakers don't care about the polarity of the incoming signal. They function normally, but then why are there polarity markings on the speaker? Take a woofer and a single battery. Keep finger on the diaphragm and apply battery voltage. You will notice the diaphragm move in or out depending upon the battery voltage polarity given to the speaker. Why is speaker polarity important? Unless you are listening to mono sound from a single speaker, there is more than one speaker in your listening environment. Destructive interference due to wrong polarity: Sound waves from multiple speakers can form destructive interference, as shown below, especially in the low-frequency range, if they are not all wired (in phase) correctly according to the polarity marked on the speaker. Problem: Weak base frequency response and misaligned stereo soun...