# Tagged Questions

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### Power factor effects and causes

Why do power utilities impose power factor penalty when power factor goes low (less than 0.7)? Why does the power factor get smaller when the load is much less than the max or rated power of ...
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### How do I calculate the effective resistance in this circuit? [closed]

How do I calculate the equivalent resistance across A and B when i) All resistors have a resistance in the given circuit of $~\mathrm{R }$? ii) The resistors in the given circuit have values as ...
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### A logic question on binary variables

I recently purchased some nightlights with sensors. The sensor will make sure the nightlight will only be tuned on in a dark environment. Let's assume the sensor is binary, ON or OFF. Here is the ...
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### Which AC bridge circuits are oscillators? [migrated]

There are different types of AC bridge circuits like the Wheatstone bridge, Maxwell, Hay, Shering and Wien. I need to know which ones are oscillators but I still don't get the main reason why the ...
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### holes in an electronic circuit [closed]

Many times, by looking at electronics circuits I noticed that they have like small holes printed in yhem. The question I want to ask is, what s the purpose of these holes?
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### Armature of electric bell [closed]

I want to know that why is the armature of the electric bell made up of soft iron ? I googled this out and everywhere it was written that it is because of its propert to aquire electromagnetism but I ...
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### Green LED Forward Voltage

Yesterday in lab, we were asked why all of our green LED had large forward voltage than expected. We expected for the forward voltage to be at around 2.1V as according to hf=Egap=eV. Yet, we ...
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### Can we “use” a capacitor while simultaneously charging it?

I know that capacitors can be charged to work like a battery . But I wanted to know whether we can charge a capacitor while it is in use ( given that the current supplied to it is more than what it ...
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### Why is the satellite dish still needed?

How much does it amplify the signal? The receiver cannot pick up the signal without the dish? Is it possible that it will disappear in 10 years? As the sensitivity of the receiver is enhanced? ...
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### Electronics book for physics undergraduates

I am going through very hard time studying electronics, I studied little electronics at high school (what is diode, transistor, etc). Now in clg now I need electronics to study, I don't understand ...
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### Normalizing temperature data of CPU sensors to ambient

My scenario: I want my application to stop or take some decision based on temperature. say like if my ambient is morethan 41 i want to switch off the application and we do not have an separate ...
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### Accelerating Hard in an EV More Wasteful?

Is accelerating hard in an electric (or any, for that matter) vehicle any more wasteful than accelerating slowly? My flimsy grasp of physics suggests that it shouldn't be. The energy required to ...
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### Kirchhoff's laws in phasor domain

While analysing AC circuits, we write voltage, current etc all with complex numbers namely "phasors". While studying the same, I wondered if Kirchhoff's laws held good with current and voltage in ...
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### Electrical Insulators

I was wondering what happens to the electron after it leaves it's valence shell and strikes a stable valence shell; in an insulating material? I realize that the energy from the strike, is absorbed by ...
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### What is the physical mechanism of power transfer in the primary of an ideal transformer?

In an ideal transformer, the mutual induction caused by the secondary load current in the primary coil generates an additional current that has a non-zero power factor with the main AC voltage source. ...
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### Can metal particles moving in high velocity combustion gas stream be charged

If we have a stream of combusted gasses in which there are micron sized metal particles moving at high speeds,can they be imparted a charge so that they move towards an oppositely charged target which ...
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### What is time badwidth product for pulses with GDD?

For a gaussian pulse the time bandwidth product is dwdt = 0.4. What is the time-bandwidth product for chirped pulse with group delay dispersion (GDD) added only ?
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### Physics of the capacitance of an electrolytic capacitor

In explanations about the electrolytic capacitor one often cites the formula $$C = \epsilon_r \epsilon_0 \frac{A}{d}$$ for the capacitance $C$. Then one says that by enlarging the area $A$ via ...
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### Voltage and reactive power

Why are reactive power and voltage related? When the control system of a generator increases/decreases the current of the rotor, voltage and reactive power are increased/decreased.What is the relation ...
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### Why fuse needs to be slightly more able to bear current than the appliance?

if I have a bulb with rated current of $4 A$ then why I need to connect an $5A$ fuse?( which has slightly more ability to bear current.)
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### Can seebeck chips be used to extract Peltier chip waste heat?

I understand that a problem with employing the Peltier effect for the purpose of cooling is that it produces a significant amount of heat on the hot plate. But why don't we use seebeck optimised chips ...
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### What happens after an electron and hole combine?

OK so I understand that an LED is a pn junction where when a forward bias is placed across the junction, the electric field causes the electrons to combine with the holes and release a photon through ...
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### Can an Oven being set to a different temperature cause electric board to go off?

Basically: the electrical system kept going off (when light goes down in a division due to too many electrical appliances on at a time, or their combined power consumption). My roommate said it was ...
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### Which law of physics is applicable for communication? [closed]

What is the physics behind communication like internet, mobile phones etc. What are the equations?
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### When heat loss is more than energy generated [closed]

Suppose a electric power station produces 200W of electricity @ 200V. Now instead of stepping it up, it decides to transmit it as 200V to a city 20 km away. The transmission cable has resistance per ...
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### Separating Interaction of Heat from Electricity?

I have a rod where electricity of frequencies 1-360 Hz is passed through. It is affected by heat. I am evaluating the energy involved in such a process, contributed by electricity and heat. The ...
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### Voltage of a battery in a circuit with an infinite resistance [closed]

I have a dilemma that I would like to share with you concerning batteries (without neglecting internal resistance), emf and resistance of a circuit. To better visualize my question you may need to ...
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### Estimate battery's real capacity in real time [duplicate]

The maximum capacity of a battery during usage can vary from manufacturer's specifications due to factors like temperatures and battery health. Because of that i want to estimate the real maximum ...
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### Electron , collision , current , dual nature [closed]

My question is regarding fundemantal concept. I am good in kcl and kvl delta to y resistor rcl and rl circuits machines etc but as i read drift velocity i get so many questions. We are reading since ...
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### Will an Electrical Engineering Minor give me a significant advantage in experimental physics? [closed]

I'm currently choosing courses to complete in my university degree (science) and thought completing some basic electrical engineering may be useful if I go into academic experimental physics research. ...
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### Books on Spectral Jacobian

Can anyone point me a book to better understand "spectral Jacobian". I am studying X-parameters, I have the book X-Parameters: Characterization, Modeling, and Design of Nonlinear RF and Microwave ...
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### Estimating the battery capacity using current power consumption and battery percentage

I want to estimate the current maximum capacity (in kWh) having the current power consumption (in kWh) and the state of charge of the battery (in %) available in a time series. I do not have a full ...
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### Why do scientists measure fundamental constants so precisely?

According to the last CODATA report the charge of electron is measured very precisely (10 decimal places). And it's not only about the charge of electron. Why do scientists measure fundamental ...
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### Why does the symbol have an arrow? [closed]

What does the arrow in the symbol mean? Does it mean that it is a variable voltmeter and ammeter?
2k views

### Why don't they use springs as an energy source for cell phones?

I know they used springs for clocks way back in the day and now it's all lithium ion batteries. For reference, consider the Iphone that has a battery with a capacity of 5 Watt hours (18,000 joules). ...
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### Why current of a battery drops continuously in high currents?

I have asked this question on EE SE but could not get a satisfactory enough answer. I have shorted an AA battery through an ammeter. Inititially, the current reading on ammeter was around 0.9 amperes ...
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### Laser-induced electrical discharge

Attracting lightning with an ion beam has been done in a lab but how strong of a laser is needed to reach the clouds to redirect the lightning bolt?
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### Why does small change in Base current causes a larger change in collector current in case of transistors? [closed]

Why does small change in the base current causes larger change in the collector current. That is say if I increase the base current buy a small amount why the collector current increases by a very ...
281 views

### Exact (quantitative) definition of “knee” and/or “cut-in” voltage?

Sort of a 2-part question: 1) I know they are used interchangeably but are the "knee" and "cut-in" voltages of a diode actually the exact same thing? I had thought that the "cut-in" voltage was ...
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### Electricity from something other than a solid

Is piezoelectricity only limited to solids or can liquids or non-Newtonian fluids create a current when compressed?
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### how to reduce the order of the hamiltonian equation for electrical problem given below?

I am having my FYP in this Hamiltonian project to analysis the integrator for Hamiltonian system. Can anyone please guide me how to reduce the equations to first order using substitution method?
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### How to reduce the order of Hamiltonian equation for electrical problem [duplicate]

I want to reduce the order of this Hamiltonian but I don't know how to proceed. The equations are given below: $$H(p,q) = \frac{1}{2} (kq^2) + \frac{p^2}{2m}$$ This is the Hamiltonian for a simple ...
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### How many photons does my remote control garage opener emit?

Every time I drive up to my house I imagine all the photons spitting out of the remote control garage opener when I press the button. And I imagine the door opener in the garage receiving them. There ...
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### Reference for Kirchhoff's Circuit Laws

Does anyone know the reference where Gustav Kirchhoff published his famous circuit laws?
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### Attenuation and Amplification - Transatlantic telecommunications cable system

It's a german book so I don't know if I'm translating this properly into english, so bear with me: The TAT-14 connects the cities Norden and Tuckerton with glass fibers (~7500 km). The cable has ...
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### Higher dimensional, generalised theoretical digital electronics

I'm learning digital engineering and I'm also a fan of theoretical and abstract physics and mathematics. I find it amazing that you have an algebra that directly corresponds to logic circuits and if ...
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### differentiate between v(rms) and V(avg/dc) of an Ac signal [duplicate]

Please differentiate between v(rms) and V(avg/dc) of an Ac signal . Why do we use rms and why is vrms called effective value; why is vp not so called or (v(avg))? And why we use v rms to calculate ...
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### How to mathematically model a realistic aperture illumination?

I want to know a mathematical expression that I can use to model a realistic aperture illumination to produce the primary beam of an antenna so that the radial distribution of this aperture ...