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127 votes

How do I prove to my physics teacher that adding a battery in parallel doesn't double the current?

Just ask her what the voltage across the resistor is
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96 votes

How do I prove to my physics teacher that adding a battery in parallel doesn't double the current?

Method 1 simulate this circuit – Schematic created using CircuitLab Figure 1. A simple practical experiment. Performing an experiment with the circuit of Figure 1 would demonstrate that ...
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86 votes
Accepted

What limits CPU speed?

Practically, what limits CPU speed is both the heat generated and the gate delays, but usually, the heat becomes a far greater issue before the latter kicks in. Recent processors are manufactured ...
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51 votes

Why are electrons not pushed out from the conductor at an open circuit under the influence of a power source?

You're imagining an open circuit to look like this: A better analogy would be this: The pipes in a circuit aren't surrounded by free space for the water to flow -- they are tunnelled through a rock. ...
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46 votes
Accepted

How did scientists deal with electronics' problems before Kirchhoff and Ohm's laws?

This is a bit like asking how Aztecs built cars without the wheel: they didn't. There was a chain of invention by scientists in the early 1800s building off each others work. Prior to then there was ...
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41 votes

How do I prove to my physics teacher that adding a battery in parallel doesn't double the current?

He said that each battery has a current of 2A if hooked up to the resistor on its own, and so they both have 2A of current through them Right. Both circuits have 2A through them. simulate this ...
40 votes

What limits CPU speed?

The heat issue is well covered by fuzzyhair. To summarize the transmission delays, consider this: The time needed for an electrical signal to cross the motherboard is now more than one clock cycle of ...
  • 2,073
36 votes

Why doesn't higher frequency mean higher data rate?

It's not a bad question and shows quite a common misunderstanding of how Radio Frequency (RF) Systems work. The 900MHz and 2600MHz signals are called Carrier Frequencies. The actual information is ...
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33 votes

How do I prove to my physics teacher that adding a battery in parallel doesn't double the current?

Others have already abundantly pointed out the teacher's wrong reasoning. I want to mention another part of this where there also seems to be some confusion. We all understand now that the current ...
32 votes
Accepted

Why do LEDs have a maximum current?

It's difficult to come up with an analogy because the usual analogies for electrical systems are fluid systems. A great thing about fluid systems is that the working fluid is also good at cooling ...
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29 votes
Accepted

Why is there no rolling shutter when using a mechanical shutter?

When I have a camera, that can take still images at 10fps with a mechanical shutter, why doesn't it mean the sensor can take images at 10fps electronically without producing rolling shutter? In order ...
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28 votes

Why are electrons not pushed out from the conductor at an open circuit under the influence of a power source?

The water analogy is very limited and does not model the way electrons move in a wire. It should always be used with great care. Electrons drift very slowly (about 1m/hour) by jumping from atom to ...
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28 votes
Accepted

Physics behind signal reflections and series termination

With electrical transmission lines, it all has to do with the speed of light being finite, thus so is the speed of EM propagation in a wire. You can think of a wire as a long series of infinitesimal ...
  • 4,603
21 votes

Physics behind signal reflections and series termination

The impedance of a transmission line, in ohms, is the ratio of voltage wave and current wave that travels down the line. For a 100 ohm line for instance, a 1 volt wave will always be accompanied by a ...
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21 votes
Accepted

Does "a signal is buried in noise" mean that the noise amplitude is still smaller than the signal amplitude? (Special case: Lock-in amplification)

What you're missing is the bandwidth, both of signal and noise. If you look at, let's say, a 1 V rms sinewave signal, together with 10 V rms noise on an oscilloscope, you'll see only noise. However, ...
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20 votes

What limits CPU speed?

There are three physical limits: Heat, gate delay and the speed of electric transmission. The world record on the highest clock speed so far is (according to this link) 8722.78 MHz The speed of ...
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20 votes

Why the prevelance of mechanical oscillators in electronic circuits?

Because the mechanical devices are much more stable than their electric counterparts. Let's compare a crystal oscillator to an LC oscillator: Crystal: Has a very high Q. According to wikipedia, a ...
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19 votes

How do I prove to my physics teacher that adding a battery in parallel doesn't double the current?

Tell her that brain farts are okay to have. It happens to the best of us. Just explain that with ohm's law it's \$I=\frac{U}{R}=\frac{80}{40}=2\text{ A}\$. In order for it to be \$4 \text{ A}\$ then ...
19 votes

Why is there no rolling shutter when using a mechanical shutter?

There are two parts to this: First, rolling shutter can still occur with (some, see note) mechanical shutters. However, this is only at short exposure times. The shutter is built out of two curtains. ...
  • 12.2k
18 votes

Acceleration when device is on tilt

Only a sketch of a solution. Take all 3 axes into consideration. Acceleration due to gravity, regardless of tilt, will always be 1G, as a vector sum of X,Y,Z, no matter what the tilt. You can ...
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18 votes

Why doesn't higher frequency mean higher data rate?

Because the bandwidth of the channel determines how rapidly the symbols on that channel can change, not the carrier frequency. It is the bandwidth of the channel which determines how fast the channel ...
  • 38.8k
16 votes

Why do LEDs have a maximum current?

There's a forward voltage drop of a couple volts across the LED. This Voltage drop times the Current is the Power dissipated in the device. It creates light, but also heat. It's the heat that kills ...
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16 votes

Is there a formula to determine the size of decoupling capacitors?

Remember decoupling has several purposes. On a load which draws transient, spiky currents like a CPU, decoupling caps store energy locally and close to the load, so it is available quickly (ie, with ...
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15 votes
Accepted

Why does capacitance value changes with applied voltage?

This quick paper from Vishay suggests that is is due to the actual dielectric constant of the ceramic capacitor significantly changing under applied electrical field strength variations (read: voltage)...
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15 votes

Color LEDs and voltage: why the discontinuity on blue?

@Math Keeps Me Busy hit the nail on the head. Look at the "Chip Technology" for each of the LEDs. Red, yellow, and green are AlInGaP. Blue is InGaN. ...
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14 votes

How do I prove to my physics teacher that adding a battery in parallel doesn't double the current?

Here is how the superposition principle is being misapplied. When we apply the superposition method, we consider each energy source in the circuit in isolation, while "turning off" the other energy ...
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14 votes
Accepted

Is there any relationship between frequency of signal and distance it travels?

In general, yes, higher frequencies attenuate more the further distance they travel. There are two effects that are responsible for this. First, higher frequency radio waves tend to be absorbed more ...
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13 votes

How do I prove to my physics teacher that adding a battery in parallel doesn't double the current?

The battery is not supplying current, it supplies voltage Your teacher is going wrong at this point: each battery provides 2A of current on its own An ideal battery does not supply a fixed ...
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12 votes
Accepted

How to understand this circuit?

Well, I just calculated the currents and voltages and I get the same results as you quote. So how did I work it all out? Well, let's re-draw your circuit with better labels, and reduce it as we go. ...
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