# Questions tagged [formula-derivation]

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### How do I calculate the Capacitance for an RC Timer to charge to ANY voltage?

We have the following simple circuit. simulate this circuit – Schematic created using CircuitLab A capacitor is being charged by an resistor of 100 ohms from a 5V power supply. Let's say I want ...
71 views

### Can Watt’s law be derived from the Ohm’s law without using calculus?

Unlike Ohm’s law Watt’s law is not a fundamental law of electronics, as it can be derived from other fundamental laws of electronics. In the derivation above (see the pic) I used definition of current ...
135 views

### How to derive transistor input impedance?

Given the following circuit, When Ro is not infinite, from the book, ZB is given as, However, when it's infinite, the input impedance is easily obtained as the parallel combination of RB and β(re+RE)...
93 views

### How to derive equation for current from parallel batteries given internal resistance and load?

I'm studying DC circuits in physics right now and have come across this frustratingly unclear part of the textbook. Apparently, the current through a circuit given ideal emf, internal resistance, and ...
1 vote
87 views

### Forward diode depletion capacitance formula

Does anybody know the forward depletion capacitance formulas for diodes in spice models? Background: The capacitance of a diode in reverse direction usually is dominated by the depletion (or junction) ...
235 views

### Zero current assumption in star - delta transformations derivations

The formula used for star delta transformations are: $$R_A = \frac{R_{AB} R_{AC}}{R_{AB}+R_{AC}+R_{BC}}$$ and $$R_{AB} = \frac{R_AR_B + R_AR_C + R_BR_C}{R_C}$$ The normal way that these formulae ...
127 views

127 views

### Inconsistency of electrical loss function

We have a function to calculate electrical losses for resistances and it is that $$P = I^2 \cdot R$$ If we consider this formula, our teachers generally say that if you want to decrease the losses, ...
1 vote
357 views

### Deriving power formulas for transmission lines

I'm trying to derive formulas for active power ($P_s$) and reactive power ($Q_s$) at the sending end of a transmission line shown below: Where: $E_s$ and $E_r$ are voltage magnitudes $X$ is ...
1 vote
491 views

### Formula for calculating instantaneous power in pure inductive and pure capacitive circuit

According to the material provided by a faculty this is what the formulas were and how they were derived. According to the derivation we did in class, we were getting: P = -VrmsIrmssin 2ωt for pure ...
1 vote
70 views

### Can someone confirm my derivation of the generalized power law from Practical Electronics, 4th edition?

I dont know how to use LaTeX, so I used Mathcha and took a snip from there.
36 views

### Looking for a formula to calculate the resitance needed to make a proximity sensor shorter! RCWL-0516

I want to decrease the range of this cheap sensor dramatically from 5m to 5cm! Im not sure which equation I use to calculate this. I'm assuming but not sure if there is a bigger resister value that I ...
200 views

### Overall Gain for Mixer Circuit

I am working on an audio mixer circuit for balanced studio gear. The circuit consists of two unity gain balanced line receivers (THAT1200), going into a pair of voltage dividers controlled by a shared ...
78 views

### Transfer function : Determination [closed]

I have the below circuit, here, I have Is and Va are measurable quantities. Rc1..Rc4 and Rbd are unknown variables for which I intend to derive transfer function. I have flexibility of adding ...
229 views

### How to derive the formula from this circuit?

This is the schematic to measure the $R_{iso}$. There is a switch, Q2 for the measurement. I need to find how to derive the $Y_{iso}$ from this circuit schematic. To find it out, I tried to use ...
1 vote
178 views

### Transfer function : Complex network

For the attached circuit attached in LTspice spice, I am trying to find the transfer function interms of Rc1,Rc2,Rc3 and Rc4. For that I have switches which I configure to turn on/off and measure the ...
39 views

1 vote
627 views

### Differential equation of a RRC circuit as Voltage output/voltage input?

So in this presentation i have got, there is a RRC circuit, and they get this differential equation, but there is no procedure explained how they have got it. This is basicially a series RRC circuit ... 135 views

### Trying to find value of two capacitors using resonant frequencies in three conditions, but wrong formula is derived

I was trying to find capacitance of two capacitors in the following way. Connect each capacitor individually to a same inductor and find resonant frequency in each case. Connect the same capacitors ...
132 views

### Derive DC motor formula with drum driving a conveyor belt

The setup is a DC motor directly connected via its shaft to a drum which drives a horizontal conveyor belt. There is a load of mass, M, on the conveyor belt. I am stuck on trying to figure out what '...
2k views

### Derive current through "charging" inductor formula

I don't know if it's just me but I can't find a single resource that derives a general equation for the current through an inductor. My text book just says "assume the equation if of the form ..." but ...
322 views

### Deriving the Integral Voltage-Current Relationship of a Capacitor

I am having trouble understanding the derivation of the capacitor voltage equation in my circuits textbook. Here is the process they followed from the textbook My confusion is: when the initial ...