Questions tagged [physics]
Physics is the natural science that involves the study of matter and its motion through space and time.
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1answer
38 views
MOSFET treshold voltage
Does anyone know how MOS treshold voltage varies if the physical distance between source and drain decreases ?
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3answers
54 views
Variable wavelength IR Diode?
I was thinking of building a DIY IR Spectroscope but for this, I need to find an IR diode that can do variable wavelengths. So far I have looked at Farnell and Mouser but all the diodes I have looked ...
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1answer
33 views
Explanation of 5 Parameter Model for Solar Cells
I am having a hard time understanding this equation, the 5 Parameter model for photovoltaic cells.
\$I = I_{ph} - I_o[\exp(\frac{V + R_sI}{nV_t})-1] - (\frac{V+R_sI}{R_{sh}})\$
My goal is to apply a ...
-1
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2answers
66 views
Three voltage sources circuit
Suppose the given circuit, find the current through the resistant R2 given
that:
E1 = 3 V
E2 = 4 V
E3 = 2 V
R1 = 1 Ω
R2 = 6 Ω
I tried to apply kirchhoff laws but it was hard given such ...
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0answers
35 views
Why doesn't current leak to ground (DC)? [duplicate]
In the circuit shown below, I am considering ground to be ideal earth ground (stays at 0V no matter how much current it absorbs). It is my understanding that current flows when there is a potential ...
6
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3answers
541 views
How do electrons carry thermal energy in Peltier coolers?
I've read that when electrons enter from metal to semiconductor type N, they gain thermal energy and make that side cooler and the reverse happens when they leave semiconductor to the conductor.
Why ...
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2answers
57 views
current speed/flow [closed]
Note
my questions are in form of explaining. its because I've scattered information (or assumptions) and it want to link them. that's probably why you can see me explaining to much?
Question part:
...
2
votes
1answer
98 views
Why are(n't) rechargeable batteries damaged by partial charging?
Over the years, I've come across websites and people with different opinions on the "correct" way to charge rechargeable batteries (I'm more concerned with laptop, tablet and phone batteries than with ...
2
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0answers
32 views
Estimate temperature for silicon (p-n junction)
I need to estimate the temperature at which p-n junction made of silicon lose it rectifying characteristics. (\$N_A=N_D=10^{15}\,cm^{-3}\$)
\$E_G\$ is independent of the temperature and are 1.12 eV ...
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1answer
35 views
Non-Corrosive Water Sensing
I have been told that passing DC current through two probes in water will lead to corrosion on the terminals.
Apparently AC does not cause corrosion. Preventing corrosion is of high importance to me....
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1answer
28 views
How to determine direction of induction current (I inc) according to V emf?
In this question, I easily understand the solution. But I want to determine the direction of induction current (I inc) with the Lenz Law. I know how works Lenz Law, but I couldn't determine the ...
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0answers
16 views
How to choose contour when finding magnetic flux density?
In this question, how we decided to use such this contour?
Also, why integral (B dot dl) the outside and sides parts are zero? At the outside part; contour and B are parallel, because of their dot ...
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2answers
39 views
Determining magnetic flux density of a closely wound toroidal coil
I am using David K. Chengs's Fundamentals of Engineering Electromagnetics book. In chapter 5/question 5.2, there is a given closely wound toroidal coil, and it asks what is the magnetic flux density ...
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4answers
108 views
Can I calculate how much time it will take for an electrical signal to propagate through a TTL circuit?
Given a particular circuit of TTL, can I calculate how much time it will take for an electrical signal to propagate through some section, or all of, the circuit?
If I wanted to know how long it ...
3
votes
2answers
149 views
What is the mechanism that causes two conductors to “stick together” when a current is passed?
If the positive and negative terminals of certain DC supplies are brought together under certain conditions, the wires will "stick together" with a slight force, feeling almost like they are ...
2
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0answers
39 views
Factors affecting the \$V_f\$ of a Schottky diode
The usual wisdom about Schottky diodes is that their \$V_f\$ is around 0.2 to 0.3 volts, but what specifically determines this?
I know that for p-n diodes, doping concentration can affect the forward ...
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votes
1answer
27 views
TVS diode with 10 - 15 V forward voltage
I came across this TVS diode: https://m.littelfuse.com/~/media/electronics/datasheets/tvs_diodes/littelfuse_tvs_diode_smf3_3_datasheet.pdf.pdf
It has a forward voltage drop of 10 to 15 V.
Why? How?
...
16
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2answers
2k views
Why the prevelance of mechanical oscillators in electronic circuits?
The clock sources in modern electronics seem to come invariably from quartz and MEMS oscillators, both of which generate vibrations mechanically. The amplitude and frequency of the vibration are ...
1
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1answer
48 views
Inductance of planar (spiral) coil near solid copper surface
I'm working on a electromagnetic levitation system, consisting of a flat spiral (planar) inductor positioned above a solid copper surface. The planar coil is parallel to the copper surface. (Consider ...
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2answers
53 views
Estimating torque of AC motor
Given voltage, measured current draw, and RPMs of an AC motor, and an estimated efficiency rating, is it possible to calculate the actual instantaneous output torque? Or is other information required?
...
-1
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1answer
29 views
Conductivity formula for Metals
Is there any expression for the direct change in conductivity of metals with temperature ?
I am aware of change in resistivity with temperature.
5
votes
1answer
86 views
Are there semiconductor materials with hole mobility greater than electron mobility?
Every material I've ever seen has a hole mobility much less than its electron mobility. For silicon, it's by a factor of two or three; for gallium arsenide it's more like twenty. But are there any ...
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2answers
198 views
How do phosporus atoms affect the conductivity of a doped semiconductor?
Free electrons come from electrons in the Phosphorus atom when it excites to the conduction band. This leave an ion, what effect does this positive ion have on the flow of electrons?
2
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1answer
65 views
Will thermocouples sharing a common wire create inaccuracies during measurement?
Specifically, I've been working with pre-existing temperature cables which are T-type thermocouples which share the same Constantan wire. My question is if one of the thermocouple junctions is heated ...
2
votes
1answer
49 views
Why do shorted PSU probes stick together just a bit, even on very low power?
I'm using a standard bench power supply set to 3.6V and 0.5A. I also tried 0.05A.
I then bring the positive and negative terminals together in a short circuit, and I noticed there is a noticable ...
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2answers
76 views
Will electrons be taken from a metal plate if a positive charge is applied to it?
If I have a single metal plate, a battery, and one wire. If I connect the wire to the positive on the battery to the metal plate, does that remove electrons from the metal plate?
I am attempting to ...
2
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3answers
110 views
Why the earth attracts charge and where does the charge go when it goes into ground?
Self-explanatory question but to add what I know, by this I will also know if I am right or wrong.
I read somewhere that Earth is positively charged, but is not the state (whether positive/negative) ...
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2answers
53 views
Effect of electron discrete nature on current density
Coulomb’s law states that the current that flows through a wire is proportional to the applied voltage. For sure there are many physical effects (linear and non-linear) that participates in the ...
1
vote
3answers
166 views
How fast can we measure using IR sensors
Supposing I have an repeatedly object passing through IR sensors and I am looking at the output waveform. What is the maximum frequency the output waveform can have?
I think this maybe related to the ...
-2
votes
1answer
134 views
Why do lead-acid batteries only last for a few years? [closed]
Why do lead-acid (automotive-style) batteries typically only last for a few years of regular use (or x amount of cycles) before having problems?
Obviously, things can't last forever. But, what are ...
2
votes
2answers
190 views
Why do electrons move as if on conveyor belt in a circuit?
For example sometimes people will ask whether it matters what side of a component you place a resistor on. Surprisingly, it doesn't matter because electrons behave as if they're all connected together ...
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vote
1answer
85 views
Sensor to distinguish between daylight and artificial light in a room?
is there a way to distinguish between daylight and artificial light in a room? I'm thinking my options are a light intensity sensor or a color temperature sensor. The sunlight is supposed to be much ...
0
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1answer
79 views
Photodiode scintillation detector for gamma spectroscopy
I'm trying to build a basic detector for x-ray or low energy gamma spectroscopy. I have a big photodiode with a CsI(Tl) scintillation crystal glued on top (Hamamatsu S8559 for x-ray detection [1]) and ...
2
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1answer
48 views
Capacitance among N conductors
I would like to have a rough estimate of the capacitance per unit length of a system composed by N parallel identical straight wires.
I tried to sketch the capacitance network but I'm able to solve it ...
14
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2answers
3k views
Why is there no rolling shutter when using a mechanical shutter?
So I know it might not be the best place to ask this question, but maybe some of you are familiar with the mechanics of digital mirrorless cameras and the technology of CMOS sensors.
I don't quite ...
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1answer
72 views
Ultrasound imaging: what are some artifacts caused by usage of time gain compensation (TGC)?
As the title asks: what are some artifacts caused by usage of time gain compensation (TGC).
2
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2answers
146 views
Electromagnet Options to Vibrate Long String at 80Hz
I recently completed a popular maker DIY where I recreated a product called SlowDance. You have see the original in action here https://player.vimeo.com/video/262079608
This product functions on the ...
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0answers
83 views
electric field on paper
This is a question set by my lecturer during a test. Sorry I still don't get the full image of Gauss Law.
A thundercloud produces a vertical electric field of magnitude 28V/m at ground level. You ...
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2answers
57 views
Phase and group velocity of wave
When an electromagnetic wave enter the waveguide, what is the change in the phase and group velocity that happen in waveguide?
Does wavelength or frequency of wave change when it enter the wave guide?...
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1answer
80 views
Why don't electrons in Parralel battery circuits repel?
Here is a short Anecdote, which will give a good explanation into my question. I was in a Science class, and we were doing a circuit with a very small Filament Light Bulb, and some AAA Batteries. I ...
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0answers
81 views
Aluminium foil not blocking IR signal
I am using an IR sensor (vishay tsop32 series) but I want to ensure that it only sender directly ahead so I made blinders out of pla and covered them in aluminium foil. However it seems that despite ...
3
votes
1answer
93 views
How does the “rubbed” coating of an LCD align liquid crystal molecules?
For many LCD applications the liquid crystal layer's relaxed state is a "helix" twisting the alignment from one direction at top to another on the bottom. Obviously, within the liquid crystal layer ...
3
votes
4answers
1k views
Potato battery not powering clock
So for a school project where we have to make a lesson plan for kids to learn stuff out of "lame" experiments, I was assigned potato clock. I could not for the life of me find a simple 1.5 volt led ...
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0answers
65 views
Peltier Module constant time and thermal Load
Hi everyone I am new to this forum.
I am doing a project where I need to control one of the sides temperature of a Peltier device against human skin. So one side is in contact with the skin, and the ...
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2answers
113 views
Electrical reactance : physical inertia analogy
Would electrical reactance and physical inertia be appropriate general analogies? Each is a resistance to change. I've thought of trying to construct a table of similarities between disciplines to ...
1
vote
1answer
182 views
How can I calculate Ampere Per Hour if Intensity has been given
Today I had an exam on Technology, and there was a question:
If a nano robot has a battery of 2.15Ah(Amper per hour) , how much it will last without recharching , if the robot spends 1.8I(Ampere) ...
2
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3answers
195 views
Why must current loop in a circuit? [duplicate]
This is a problem that's bothering me for a while, and I'm going off accepting other people's claims rather than figuring out the first principles of circuits.
Consider this circuit right here. From ...
11
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7answers
330 views
Saturated BJT Transistors. \$V_{CE} < V_{BE}\$ : AKA - Things that make you go “Hmmmm”
We use them every day and those in the know fully understand the functional characteristics of BJT transistors. There are documents and links galore explaining the operational math. There are even ...
2
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2answers
103 views
Doubts on Semiconductor Physics
I'm really confused about the working of a Bipolar Junction Transistor (N-P-N).
Just consider the below figure:
1) Clearly the Base-Emitter junction is forward biased and Base-Collector junction is ...
81
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18answers
22k views
How do I prove to my physics teacher that adding a battery in parallel doesn't double the current?
simulate this circuit – Schematic created using CircuitLab
My physics teacher said that the current through the resistor is 4A because each battery has a current of 2A if hooked up to the ...
