Negative Definition and 1000 Threads

Hi everyone! I'm trying to understand why when writing the differential equation of a discharging RC circuit V_C-Ri(t)=0 \to q(t)/C - Ri(t)=0 we replace i(t) with -\frac{dq(t)}{dt}. I read many threads but I don't understand the physics behind this. The usual answers I read are something like...

##R_{X} = \sum F_{X}## ##R_{X} = 750.sin 60^{0} + 250## ##R_{X} = 899.52 N## to the right. ##R_{y} = \sum F_{y}## ##R_{y} = 750.cos 60^{0} - 1250## ##R_{y} = - 875 N## ##R_{y} = 875 N ## downward ##R = \sqrt {R_{x}^{2} + R_{y}^{2}}## ##R = 1254.89 N## ## tan θ_{X} = \large \frac...

$$W = - \int _ { a } ^ { b } \vec { F } \cdot d \vec { r }$$ ( The Force here is referring to the applied force, When moving a positive charge towards another positive charge(stationary) / field In this formula why there is a negative sign in the formula? I am not asking the sign of the total...

I have to find resultant for this couples: My sir resolved given forces into components like this: He considered Fx couples for sides 3,4,5 triangles: He wrote resultant force for this above diagram: ##\Sigma F_x = \textbf{-}2*\frac{4F}{5}##

we know that if the applied force is in the direction of the displacement then work done is positive.But in case of bringing 2 opposite charges from infinite to a certain distance,the work done is negative even the force and the displacement of the charge is in the same direction. From...

Equations: Question: Using the equation for t' I got the answer -0.00000499756s (Wrong anyway) As we know the values: v = 0.67c m/s x = 3900 m t = 0.000005 s Also how can time be negative? Does this mean that event 2 happened before the first event when t = 0?

In Mathematical Methods in the Physical Sciences by Mary Boas, the author defines the Laplace transform as... $${L(f)=}\int_0^\infty{f(t)}e^{-pt}{dt=F(p)}$$ The author then states that "...since we integrate from 0 to ##\infty##, ##{L(f)}## is the same no matter how ##{f(t)}## is defined for...

We express such equations by $$\frac{dx}{dt} = \beta - \gamma \cdot x$$, t denotes the time. In this case, γ depends on x, thus the dynamic equation should probably be: $$\frac{dx}{dt} = \beta - \gamma(x) \cdot x$$ 1. Setting the equation to 0 leads to two different cases: If x < K: xST = γlow...

Negative Hydrogen Ions in Cyclotrons and elsewhere I was vaguely aware that negative hydrogen ions are used in some cyclotrons and this improves beam current. I've been thinking about this recently after noting that hydrogen is actually quite electronegative in comparison to most metals (just...

From my understanding, the root locus is only concerned with open loop gain. I figured this means you would ignore the negative feedback loop and calculate the root locus from just the plant's function Workings: zeros: -1 poles: 0, -2, -2, relative degree = 2 => 90-degree asymptotes meeting...

How can a negative charge move towards a position of a higher electric potential from lower potential but lose electric potential energy?From my understanding, I understand that for a positive charge, it must lose potential energy from the electric field as work is done by the electric force in...

What does it mean for an orbit to have a negative inclination? is it equivalent to an orbit with the same positive inclination but a shift in the node \Omega by \pi ?

Hi all, I’m having some trouble finding a minus sign in a standard calculation I have been doing. I am trying to show that if there is no enclosed current around the example loop in the enclosed jpeg, the four piecewise paths add up to zero (for the line integral part of Amp’s law). For this...

I have a question on what happens to MOS capacitance Cgs+Cgd, when Vgs goes negative in the NMOS shown. I see that when Vgs goes negative, the channel is full of holes because of p- substrate, which means we see the Cox capacitance (without any other capacitance in series), but I am not sure if...

Homework Statement -2^x = y Homework EquationsThe Attempt at a Solution When I plug this function in my graphing calculator, it appears to be 2^x reflected across the x axis. This doesn't make sense to me. For example, for x values of 1 and 2, the value of y is not on the same half of the...

Homework Statement I have a material placed between parallel plates depleted of free electrons and contain negative ions. What would happen to the charge stored across the plates? Would it still be similar to placing a capacitor with a di-electric constant between them? Homework Equations Q=CV...

Its stated that empty universe should have a hyperbolic geometry (Milne Universe) but I don't understand how its possible. $$H^2=\frac {8\pi G\epsilon} {3c^2}-\frac {\kappa c^2} {R^2a^2(t)}$$For an empty universe when we set ##\epsilon=0## we get $$H^2=\frac {-\kappa c^2} {a^2(t)}$$...

How could we detect negative mass matter? The only proposal I've ever heard of is that we could detect there's a cutoff frequency in the gravitational waves we receive, due to attenuation of those lower frequency waves by negative matter. Are there more experiments that could be conducted...

does somebody with a negative mass create a white hole instead of a black hole because of its anti gravity property.

Excuse me for bad wording in the title, but there is only so much you can do with the character limit. So, has there ever been a proposal for a mechanism through which negative energy density could be created? Or the only possibility considered so far was that it would have been created in the...

what are the negative effect of hystersis in metals or negative effects of magnetic hystersis for electrical hystersi over heatin in wires causing low energy transfer and effency

Homework Statement I am revising on the derivation of the differential equation of energy (White's Fluid Mechanics 7th ed) and I'm having trouble understanding the sign convention used in the viscous work term. The textbook first define an elemental control volume and list out the inlet...

Any thoughts on this paper? https://arxiv.org/abs/1712.07962

Homework Statement A line makes some angle T with each of x and z axis, and angle U with y-axis so that sin^2(U)=3sin^2(T). Homework Equations 2cos^2(T)+cos^2(U)=1 ...(i) cos^2(x)+sin^2(x)=1 The Attempt at a Solution Using the above two eqns. give us the correct value for cos^2(T) which is 3/5...

Hey, I'm designing an HVAC system for a laundry building. I have vacuum equipment (Vacuum press and Vacuum Ironing boards ) in the space which have a vacuum outlet the is taken outside the building through individual ducts. When all machines are operational, 877 l/s of hot air and moisture would...

Kindly help me with this. Solve i^(-21/2) Note: i means iota.

Homework Statement Find ##R_4## for ##g(x)=cos(πx)## on ##[0,1]## Homework EquationsThe Attempt at a Solution (i) Since we want ##n=4## even sub intervals between ##x=0## and ##x=1##, intervals are ##[0, \frac{π}{4}]##, ##[\frac{π}{4}, \frac{π}{2}]##, ##[\frac{π}{2}, \frac{3π}{4}]##...

Yesterday I wrote a simple computer simulation for a spring which, when released, sends two masses flying in opposite directions, and views the event from two different reference frames. My goal was just to convince myself that relativistic mechanics is self-consistent and indeed every time I...

Homework Statement prove (5-n^2)/(3n+1) diverges to negative infinity as n approaches infinity Homework Equations For all M>0 there exists an N in the natural numbers such that for all n >= N, x_n <= -M The Attempt at a Solution Let M be an element of the field of the real numbers. Let N in...

What is error in the picture?

Homework Statement The question askes about the path of the electron. I need to know if I am doing it correctly whether it was asked for a proton or an electron. Homework Equations F=QV⊥Bsinθ The Attempt at a Solution I answered it C. Because it is an electron, I used my left hand. My thumb...

Why can't we have modulo negative number? I have never seen this.

Homework Statement If x1 and x2 are the initial and the final position vectors of particle respectively. Then, displacement of the particle is delta x = x2 - x1 But my question is how to know that the displacement is negtivive and its direaction? (could you provide a practical example so that I...

Question: A distance R is measured to be 3.400 ± 0.007m. What is the absolute uncertainty in R^−2? Attempted solution: Relative uncertainty: 2* (0.007/3.4) = 4.11E-3; R^-2 = 3.4^-2 = 0.0865 m^-2; Absolute uncertainty = R^-2 * relative = 0.0865 * 4.11E-3 = 3E-4 m^-2; Any help would be greatly...

If we split H2S we get H2S = 2H+ + S2- Where does the negative charge come from in H2S? Do we get 2- charge from the 2H atoms (now two protons after losing the electrons), I mean 2H+ or 2 protons get separated leaving behind the two electrons on S?

In a coordinate bond, why H^+ atom don't get the negative charge? as an example [NH4]^+ If we split [NH4]^+, we get NH3 + H^+. In NH3, N and 3H atoms have completed their octet and H^+ accepts the lone pair of electrons from the N, As we know H^+ has no any electrons but a proton. If it receives...

Homework Statement So this is a problem I've been facing while finding the area under some curves, for example finding the area bounded by sinx and cosx between pi/4 and 5pi/4. integrating sinx-cosx with these limits would result in the positive and negative areas cancelling out, how do I get...

So, velocity is a vector, right? And vectors can't have negative magnitudes, right? Then why is leftward velocity considered negative in 1D kinematics? It just seems off to me. Same with acceleration, and pretty much _every vector in all of physics._

I'm going over applications of logarithms in my College Algebra class and I'm at a part where it talks about pH scales, and it shows the pH concentration of a substance to be the negative logarithm of hydronium ions. I want to know why the logarithm is negative, so I googled it and the answers...

Allegedly, string theory (in it's simplest form) predicts that cosmological constant must be negative (or zero). Can someone explain where does this result come from? A reference would also be welcome.

I'm trying to find ##\sin (\arccos x)##. I let ##\theta = \arccos x## and then use ##\sin ^2 \theta + \cos ^2 \theta = 1##, I get ##\sin (\arccos x) = \pm \sqrt{1 - x^2}##. I'm not sure whether to take the positive or negative root. On Wolfram Alpha is shows that the result is the positive root...

The following from Wiki re Hawking Radiation:“... vacuum fluctuations cause a particle–antiparticle pair to appear close to the event horizon of a black hole. One of the pair falls into the black hole while the other escapes. In order to preserve total energy, the particle that fell into the...

Homework Statement Homework EquationsThe Attempt at a Solution Was wonder how the isotherm is negative? Is it because it is going counterclockwise (the arrows)? If this is the case, i don't see why a-c would be positive work... I'm just confused on whether work should be positive or...

Homework Statement I am conducting an experiment where I am interested in finding the absorption coefficient of different materials as muons pass through them. My data was all well until I realized more muons were measured AFTER they passed through one of the materials, which makes no sense...

I'm currently developing a heat sink for a product that produces up to 150 W max power dissipation. I'm currently getting a negative thermal resistance for the heat sink. I don't think that is possible.. I'm not sure how to move on at this point to properly design a heat sink to meet the heat...

In refraction of spherical surfaces, We derived the formula to be: ## u_2 L^{'} = u_1 L + (u_2 - u_1) R## Where ##L^{'}## is the reciprocal of the distance of the image. ##L## is the reciprocal of the distance of the object. ##u_2## is the refractive index of the medium that the light ray is...

Homework Statement Homework EquationsThe Attempt at a Solution I thought it would become d/dx(-kAc*dT/dx)+hp(T-T)=0 instead of where the equation in the red box? I don't see how are they equivalent [/B]

If an electron starts from rest 85.0 cm from a negative fixed source charge of -0.135 micro coulombs we use the equation ke final - ke intial + pe final - pe intial. In solving you use ke = pe which appears to cancel out the inital kinetic and potential energy but how can the initial potential...

Homework Statement Hi, Here is what I know about the Ideal Op-Amp. - The open loop voltage gain is infinite - The output voltage is given by the following $$v_o = A(v_+ - v_-)$$ - Only with a negative feedback loop is $$ v_+ = v_-$$ My query is with regards to the negative feedback loop...

Hi, I recently tried to create diffraction gratings using the negative film of a disposable camera. I designed them so the 'slits' were black and the rest was white so on the negative film the slits would be transparent and the rest would be opaque. It didn't work however. Does anybody have any...