# Questions tagged [math]

Math or Mathematics is the abstract study of topics such as quantity (numbers), structure, space, and change.

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### Why does tan (θ) equals -j in impedance of reactive circuits?

I'm having trouble understanding the maths for impedance. Suppose we have a voltage of $V(t)=V_{0}sin({\omega}t)$ and we plug this into the capacitor equation $I(t)=C\frac{dV(t)}{dt}$. This would ...
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1 vote
64 views

### Beat frequency - Square signal

This question comes from this one, LTspice - Beat frequency: It appears that when I did a FFT of two sinusoidal signals, there was no what is called beat frequency. When I do the same exercice with ...
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1 vote
100 views

### LTspice - Beat frequency

Here is the theory from wikipedia: Here are my summation of sin on LTspice: The frequencies are 100 kHz and 120 kHz on the FFT. There is no frequencies at (f1+f2)/2 and no frequencies at (f1-f2)/2. ...
• 2,478
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### Where am I wrong in my derivation of RC charging circuit equation?

I'm trying to derive the RC charging circuit equation for capacitor voltage $V_C$ and charging time $t$. Here's my solution, We'll start by assuming the battery, resistor and capacitor are ...
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124 views

### How is CRC5 calculated in detail for a USB token?

How is CRC5 calculated in detail for a USB token? ...
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1 vote
93 views

### How to find the power factor of a component when the combined power factor and one other power factor is known? [closed]

Problem: A 2000 volt-ampere with a power factor of 0.8 lagging is combined with 500 volt-amperes of synchronous motors. If the overall power factor is 0.9 lagging, find the power factor of the ...
1 vote
74 views

### Polarization Derivation

Can how I can find the phi and theta unit vectors as described (Eq. 4a and 4b) in the following paper on antenna cross polarization? I thought the thetha and phi unit vectors were the same as those of ...
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40 views

### How do I relate input and output signals and find the output for other input signals in LTI system?

I am studying about signals and systems. I came across a few practice problems. For the below question, I was able to mimic the input and output waves shown in ...
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157 views

1 vote
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### Finding an analytical expression for a current distribution for conductors in parallel

Recently, I tried to set up an experiment at home to study what path the current takes at different frequencies for the circuit below. I think this will be a fun project, but I'll need your help. I ...
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641 views

### Calculating inverse fourier transform and graphing it

Recently I stumbled upon Fourier transforms which means I am very new to it. I've been given a question from my professor to find the inverse Fourier transform of a frequency spectrum which is given ...
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1 vote
206 views

### Construction of a Lagrangian function for a circuit

I was reading the paper "Introduction to quantum electromagnetic circuits", by U. Vool and M. Devoret and I am stuck in the construction of a Lagrangian function for the example LC circuit ...
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### Self-capacitance formula for planar inductors

I'm designing a Rectangular Planar Spiral inductor with a rectangular conductor cross-section (it's not made from cylindrical wire) for use in an RLC circuit (an NFC tag), and I can not optimise the ...
1 vote
386 views

### How to calculate the resistor values for the zener diode and the BJT base?

I try to convert ~12V signal from a car button (the input voltage can be from 10V to 14V) to a logic level signal for MCU, but the signal should to be inverted (1 = 0, 0 = 1). Below is my schema, but ...
2k views

### What do the poles and zeros of a system physically represent?

I've been working with transfer functions and control models for a while, but I never really have gotten an intuitive understanding of what the poles and zeros of a system really represent. I was ...
58 views

### How did he calculate the error in this example?

He found an error of about 18%. What is the error formula used in this example? From section 1.5.1 of the book Design of PLLs by Behzad Razav.
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### Where to start theremin project

I am studying electronics and would like to design a theremin that uses discrete components. I have read that RF oscillators such as those needed for a theremin are not likely to work if built on a ...
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31 views

### Am I solving this capacitance equation correctly?

The following is a datasheet excerpt about satisfying the clock-signal requirements for a low pass filter When using the internal oscillator, the capacitance (COSC) from CLK to ground determines the ...
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