Resistance Definition and 1000 Threads

why smaller cross-sectional area increases the resistance of a conductor?

The diagram of the BJT amplifier small signal model is below. This is not really a homework question as I am self-learning electronics, but I was advised it may be better placed here than in the technical portion of the forum. Thus I do not have an "attempt" at a solution (which is given as RI...

Have been busy working with a student doing a Physics prac to determine the internal resistance of an AA 1.5 V (nominal) battery. The basic formula being investigated is: $$Vt=E_{cell}−Ir_i$$ where ##Vt## is the load (resistive only) voltage, ##E_{cell}## is the emf of the AA battery, ##I## is...

i don´t understand the question

[Thread moved from the technical forums to the schoolwork forums by the Mentors] Hi i have this assignment for homework: There is only one battery for the circuit, E=10V, R=4 Ohms and L=1H it asks me to find the time constant of the circuit. i know that a time constant in a RL circuit is t=L/R...

Mentor note: Moved from a technical forum section, so Homework Template is not present. Hello Physics Forums members, I am a student in AP Physics C and I was just working out the range of a projectile when air resistance is non-negligible. As of right now I'm going to use the linear model of...

T=R/C So: 0.003s=R/100μC R=3*10^-7Ω I am really confused with the equations I have to use

Full problem: I don't normally think about circuits like these in terms of energy (Joules) so I was very much confused. What I did was find where the simplified expressions intercepts with each other to get the voltage. I scanned in my work although this text is a walk through of what I did...

Hello guys, can anyone help me to understand why an increase in peripheral resistance causes an increase in the blood pressure? If we assume the equation Delta P = R times Q If we assume Q is constant, the greater the resistance the greater the the decrease in pressure, so the pressure should...

I know that friction on a surface has a maximum value. When an object is pushed with a force greater than the maximum friction value, the object will move. But when a free-falling object falls from a height, does air resistance have a maximum value as well?

Lets suppose a half ring whit internal radius a and external radius b and height t. We can calculate the resistance of the half ring considering that it is made of a number of parallel resistors each one with resistance given by: R = ρ L/S where L = π·r and S = t·dr. The resistance of each...

We are given the resistivity of Gold. The length will be the outer radius minus the inner radius. We need to find the area. But I'm not sure how that would work given the spherical nature of the particle Would we need to use an integral to add up the increasing cross sectional area from the...

Voltage SI unit = Volts Current SI unit = Ampere Resistance SI unit = Ohm Ohm's law : V=IR Did Georg Ohm (German), Ampere (French) & Volta (Italian) collaborated when Ohm came out with this electricity equation with units for voltage, current & resistance as per their surnames? Credit goes to...

Summary:: What is the sliding resistance of an eccentrically loaded block on a flat surface? If a 1000kg block is placed on a flat surface (say coeff. of friction = 0.4), what force does it take to slide if it loaded eccentrically, i.e. at the far edge of the block? My thinking is there is...

Back in grade 10..,.( Oh my that was awhile back 😀 ) our electronics teacher passed around a multimeter and everyone measured their resistance ( a lead held in each hand, Fluke was set on infinite ). All in the class measured between 700K and 800K approx. All except me that is. I measured 1.4M...

Context: What I don't understand is why the little current that flows through the converted voltmeter can affect the measurement when the resistance of the resistor added to the ammeter is not infinite. Can someone please explain this to me? Thanks.

Why in an electric circuit with only a generator the resistance R=infinity? [Newbie's post edited by a Mentor to delete extraneous embellishment]

I am asked to find Ro, a, and b. Th problem states the values are determined by the measurements at the normal ice, steam and sulfur points. So I approached the problem by plugging the the temperature problems. For 0°C, Ro reduces to 7 ohms. Then for the other two non zero temperatures, it looks...

The resistors are all in series , with exception of R, so I added them together and then used the current divider equation to solve for R, and I got 720 ohms. The textbook says R should be 30 ohms. I’m completely lost.

For the electrical resistance ##R## of an ideal wire, we all know the formula ##R=\rho * \frac{l}{A}##. However this is only valid for a cylinder with constant cross sectional area ##A##. In a cone the cross section area is reduced over its height (or length ##l##). What is a good general...

Paper has a grain direction – the direction of the long fibres. For several reasons, publishers always print hardcover books with the grain of the paper in the same direction as the fold. I'm working on a book that will be 2:1 wire bound (two holes to the inch). I was wondering what the grain...

I check the datasheet of LM 319 high speed comparator online. I was wondering if LM 319 can accept negative supply voltage(-10V) and its possible to produce a 10V to -10V square wave which oscillates along origin rather than just 10V to 0v as shown below.

NOTE: THE C1 that is 120 microfarads is meant to be C3. What I did first was find equivalent capacitance of C2 and C3 by doing (40)*(120)/(40+120)=30. Then I found Ceq by doing (20)*(30)/(20+30)=12. For the resistance I did 6*3/(6+3)=2, for R2 and R1. Then to find Req I did (5)*(2)/5+2= 10/7 Am...

Hey! I had a question about this problem. I did (1) Using $$R_{0}=\rho\frac{l}{A}$$ For (2) I assume the question means that the radius increases by a meter. So I used $$\bigtriangleup L = 2\pi (r_{E}+1) - l$$ and then I used that L to find the new R. Then I said $$\bigtriangleup R = R-R_{0}$$...

ANSWER: element x does not present a linear resistance because it isn't constant as i and v increases. Is my answer correct?

Let imagine that car with constant 500HP accelerate but resistance forces don't exist (aero drag,internal friction in engine and transmision,tyer rolling resistance etc etc..) neglect fuel loss over time.. From 0-100km/h take in 4sec and burn 200mL petrol Will car accelerate from...

I have a question about an exercise I don't understand, I don't want the solution, only the first element to begin. I have tried with kirchhoff law, but I failed. thanks

I don't really have any equations or idea how to solve this. I searched for relevant equations and only R=Rref(1+α(T-Tref)) pops up. I wasn't given any temperatures so I guess there must be some other way to solve this. Maybe anyone has idea how to approach this?

What the question mean by "constant frictional resistance" in terms of formula? I suppose they meant... "resistance force (f)" which is, >> f = m * a. So, here is my try... m = 1.15 ton or 1150 kg vi = 20 m/s vf = 0 d = 800 m v^2 - u^2 = 2ad 0 - 20^2 = 2a* 800 - 400 = 2a* 800 - 400 /...

Hi, This has long been in my head, I've seen it work out in reality, but I have no idea about the forces involved in this. As I don't have an engineering degree or mathematical knowledge in automotive engineering, I've come here for help. Sorry if I've used some terms where they do not fit, as...

I am not sure how to even start this problem.

I know the answers are 9 V and .5 ohms but I have no idea how to get there. Originally I solved for Delta V in the open circuit through (1.636)(5) which gave me 8.18V. Then, I solved for Delta V in the closed circuit through (1.565)(1/((1/5)+(1/10)) which gave me 5.51 V. I used these voltages...

Here's a little snack; what is the resistance between two small conducting spheres, each of radius ##r##, separated by a distance ##d \gg r## within a material of resistivity ##\rho## (of infinite expanse)?

Changing the temperature of a metal changes the resistivity. But It also changes the size of a sample under test. Does the change in size have an additional effect on the resistance or is that already factored in ?

Back in June 2020, in São Paulo, Brazil, Thais Andrade has avoided infection with Covid-19 though her husband, Erik Soares de Araujo, fell seriously ill and had to be hospitalized. https://www.statnews.com/2021/08/23/lucky-few-seem-resistant-to-covid19-scientists-want-to-know-why/ Scientists...

a) Output voltage = 2 x 6 = 12 V Current in R = 12 V / 13.5 kΩ = 8.9 x 10-4 A That is the correct answer based on the solution but I don't understand why when calculating the current in R, the resistance of secondary coil is not considered. I thought it should be like this: Current in R = 12...

The question is to find the resistance between AF (top 2 points). Let the far right unlabelled vertex of the pentagon be B. Why can we say that points O and C are at the same potential? I get that both points O and C appear to be at 'half the path' if you consider AOF and ABCDF, and so potential...

Well, if the Delta variant wasn't enough, now this seems to be rearing it's head. Also continued https://news.yahoo.com/delta-infections-among-vaccinated-likely-192553854.html

why is answer for (6a)6J?

Hi i got a question ,how do i calculate the input resistance ,of the RS resistor ,so i would get half of the voltage of the voltage source (500mA) .I've created the circuit in ltspice and found out that its around 95K ohms to get 250mA,but how would i calculate it . Ive also attached my...

When current starts flowing in a circuit, voltage of the battery drops from EMF value. There are three sources of this however here I am only interested in ohmic resistance of the battery. EMF of the battery is created because of electrochemical processes on both electrodes which create...

I know that the resistance of an ohmic conductor increases with length because the electrons going through the conductor must undergo more collisions in a longer conductor. But why decreasing the cross-sectional area of the conductor also increases the resistance of a conductor?

I'm working with some bare chip diodes for an application where I need extreme luminosity. These are the diodes here: https://www.irtronix.com/leuv-v625a6 I notice that some of the diodes have very significant resistance (on the order of megaohms) from anode to cathode and some have very small...

i don't understand the answer: Nichrome has a higher resistance than copper wire. There is a greater potential difference across the nichrome than the copper wire. From ,the resistance of nichrome is low enough such that there is significant power output. ^ i feel like the bold parts contradict...

i keep getting 45.3 ohms but the answer is 25.6 ohms

The true answer is : The voltage between P and Q is 1.5 V. I got stuck finding the total resistance. My question is: Is B parallel to both A and C? Is C parallel to D ? I tried many ways to find the total R but failed! My first attempt: I say the system ABD is in serie with C...

Disclaimer: Some of you might easily recognize that the components and circuit I am talking about are related to one of my projects, on which I had posted some months ago. Actually, the circuit is the same as the one in my project, but the one I am posting in this thread actually uses high...

I was following these [steps](https://www.allaboutcircuits.com/textbook/direct-current/chpt-10/delta-y-and-y-conversions/). I was calculating resistance for left side circuit. $$R_1=\frac{2 × 2}{2+2+4}=0.5\Omega$$ $$R_2=\frac{2 × 4}{2+2+4}=1\Omega$$ $$R_3=\frac{2 × 4}{2+2+4}=1\Omega$$ Then...

Am trying to find Effects of Feedback - Input resistance of this circuit. Is this the formula that in need to use to find the input resistance of this circuit ?