Resistivity Definition and 189 Threads

We see always in source meter machines a LED which indicates the limit current. I want to know what is the limit current and what is the relationship between this later and the resistivity.

Homework Statement For some applications it is important to minimize the temperature dependence of electronic components. For example, there is a special alloy called constantan that can be used for temperature independent resistance elements. Do you expect constantan to have a high or low...

so this is the question I'm having a little trouble with: Assume that the ratio of copper resistivity at room and absolute zero temperatures (so called "residual resistance ratio") is 1000. Estimate the electron mean free path in copper at low temperatures. we also know this: Let us assume...

Homework Statement Dry air has a resistivity of about 3*10^13 Ωm. A capacitor has square plates 10cm on a side separated by 1.2mm of dry air. The capacitor is charged to 250V. Assuming the potential difference does not change as the charge flows, what fraction of the charge will flow across the...

Homework Statement Estimate the resistivity of an amorphous metal whose mean free path is of the order of an atomic spacing. Compare your answer to crystalline copper.Homework Equations VF = h(bar) KF / m VF = l / τ ρ = m / n e2 τ The Attempt at a Solution I think my real issue with this...

I am studying on Fe powder samples. I have used I-V measurement system to get resistivty. However, I would like to measure with 4-point probe. but I am confused how to prepare the powder sample for 4-point probe. could you tell me there is a way?

Does anybody understand the fundamentals of what is happening in this circuit? Tungsten welding info is all about high current... but this is a low current scenario. AC input, CDI Coil generated 20Kv (estimated) suffers voltage drop over 100mm of tungsten rod. The larger the diameter... the...

Hello, I am curious why in the resistivity formula you divide the length by the area? R=P*(L/A). I cannot figure why you would not take the L*A to get volume?

[SIZE="4"]Definition/Summary For a given material, the resistance of a length of the material is a constant times its length, and divided by its cross-section area. This constant is the resistivity, \rho, of the material. Resistivity of a material is measured in ohm-metres (\Omega m)...

I have a question regarding "ohm level" in a heating element in the design of a device designed to vaporize a liquid. I thought I had a pretty solid understanding of this but I've been told that I was wrong. So, I thought that if you increase the resistance (higher ohm) in a heating...

If I have a pair of coils connected in an anti-helmholtz configuration, with current flowing oppositely in both, and I wanted to calculate the resistivity- wouldn't the length of both coils just be summed up? I tried this but I am not getting the answer I want.

I am very sorry because this post seems spammy, but I cannot, for the life of me, find the resistivity of NiCu alloy. My lab has it as 35*10^8 Ω*m, and when i compare my calculated value of resistance to the theoretical it is off by a factor of 10. This causes me to think that there is a...

How do I calculate the resistivity of a doped Si if I have to substrate of the same type. Let's say a P and As doped Si. Is the mobility given by, \mu_n(N_d + N_d), or should I do this in an other way? Further, when I calculate the resistivity, is the concentration, N_{tot} = N_d(P)+N_d(As) ...

Homework Statement Determine the length of the shunt if the c.s.a of the copper is 25cm^2. Homework Equations R = ρ l/a Resistance of shunt is 0.5μΩ The Attempt at a Solution Transposing to find l. l = AR/ρ =25^2x10^2 x 0.5x10-6/1.7x10-8 =7.4mm is the length of the shunt...

Homework Statement A number 12 copper wire has a diameter of 2.053mm. Calculate the resistance of a 31m long piece of such wire. Use rho=1.72x10-8 Ohm-m for the resistivity of copper. Homework Equations This is the part that I am unsure of, all of my equations for resistivity do not...

Hello All, I was curious to know if there is a way to calculate resistivity of a wire that did not have a uniform cross section? For example, what if the cable was in a bow-tie geometry? Is there anyway to quantify the electrical resistivity of the constriction (the area of the cable that has...

Homework Statement Homework Equations R=pL/A The Attempt at a Solution The answer is C and I don't know why. If R = pL/A then isn't L=b between X and Y?

Hi all, I have been searching the internet for explanations on the method of ERT, but they are in general extremely complex and contain very specific vocab that I'm not understanding. Would somebody care to explain to me the method of ERT in language that an A Level student can understand...

Hi all, I am writing an assignment at the moment, asking me to report on the use of resistivity in identifying objects under the ground. I've gotten confused as to whether resistivity is used at all - surely resistance is all that is needed? For example, in any multi probe resistive survey, the...

Homework Statement A) To= 35 °C find α And β B) determine the temp in which this material becomes a super conductor as predicted by the equation below. ρ=ρ0(1 + α(T-To) + β(T-To)^2)To= 35 C. ρo=2.5e-8Ω m T1= 0 C. ρ1=2.346e-8Ω m T2= 100 C. ρ2=3.036e-8Ω mHomework Equations ρ=ρ0(1 +...

Hello, In my lab report, I am trying to discuss what the units of resistivity mean. For instance, the unit of speed m/s second can be described as the time it takes to travel 1 m; specifically, 50 m/s would say that it would take 1 s to travel 50 m, or, we travel 50 m every second. Could...

the electrical resistivity ρ of a metal is proportional to the probability that an electron is seattered by the vibrating atoms in the lattice an this probability is in turn proportional to the mean square amplitude of vibration of these atoms.How dose the electrical resistivity ρ of the metal...

Hai, I am doing my masters degree in physics. can somebody help me in which formula to use for calculating resistivity of a sample of circular shape using two probe measurements, which should include thickness and correction factor also. Thank You!

I am studying the resistivity of various materials in my physics class and I have a query regarding conductive fluids. If a current is running through a fluid (let's say water) within a rectangular beaker, and there are two copper wires put in at opposite ends of a beaker (I believe they are...

Hi I was wondering if anyone could help. My teacher isn't very good at explaining things and he's given us a question without going through the reasoning behind the equation. Aluminium wire has a resistance of .250Ω at 0°C. Give that the temperature coefficient of resistivity at 0°C for...

Hi everyone, - Could you explain for me the meaning of "net" in the phrase "small net attraction between electrons" in superconductivity, (or synonym of it)? - We usually say that BSC theory explains the superconductivity of conventional superconductors, one feature of superconductivity is...

Hello All, I am a graduate student conducting a shallow subsurface geophysics study over closed landfill cells and have run into a bit of a problem with my data collection. I have ran traverses spaced 10 m apart running E to W across cells with all traverse lines ran twice using two...

Homework Statement A long wire connected to the terminals of a 12V battery has 6.4 x 1019 electrons passing a cross section of wire each second. calculate it's resistance. answer is 1.2ΩHomework Equations q = ne q = IE R=ρ L/AThe Attempt at a Solution V= 12v n= 6.4 x 1019 electrons R=? First...

I'm trying to find the resistivity of conducting putty at room temperature and I've been looking all over google with no success. There isn't really anything more I can do to work it out so I'm wondering if anyone here knows. Thanks :)

Is it any model on resisivity of two tightly-attached coaxial cylinder? For example, a copper core wire is coated with layer of aluminum. How to calculate the final resistivity along axis?

This question has bogged me down for hours. Please help. An alloy of metals is found to have a resistivity of 1.2e-6Ωm at 300K. When it is heated to a temperature of 973K, the resistivity is found to increase by 10 per cent. Assuming Mathiessen's rule to hold good for the alloy, find its...

Homework Statement The resistivity of nichrome wire is 1.1micro ohm meters. What length of wire of diameter 0.079 mm is required to provide resistance of 1.0 Kohm? Homework Equations R=resistivity x length/area The Attempt at a Solution 1000ohms = ? x 0.0011/0.079 79 = ? x...

Every year we do an experiment to find the resistivity of Nichrome wire, and every year the result is the same: 5 x 10^-7 instead of 1 x 10^-6. For the life of me I haven't been able to track down why it's a factor of 2 off. We use a Wheatstone bridge that has a 1 m length Nichrome wire...

12-gauge copper wire has a radius of 1.03×10−3 m. (a) What is the resistance of 11.5 m of this wire at 20°C. (b) How much current will pass through the wire if a potential difference of 9.00 V is applied across it? The resistivity for copper is 1.7E-8 ohm meters For part a: The equation is...

In "Electrons and Phonons" by Ziman which you can find here, I have a problem with equation (9.5.14) on page 360 and (9.5.17) on page 361. I don't understand how from the first equation where you have double surface integral you obtain the second equation with only one integral over q. I...

silicon has a negative temperature coefficient of resistivity. So that means that it's resistivity decreases as temperature increases. How is that possible? Also, would that mean that at some certain temperature higher than room temp, silicon would act as superconductor? It has a very high...

Hello everyone I am trying to do an experiment involving a W bulb, in which I am completely dependent of knowing the temperature-resistivity relation of Tungsten in the temperature range 300 - 2500 K. The CRC handbook has some tables, but they have few data points and correlate poorly with...

Homework Statement A conducting wire has a resistivity, ρ as a function of its length, L, given by ρ=(ρ0)(L) where (ρ0) is constant. A is the cross-sectional area of the wire. the resistance of the wire would be A) [(ρ0)(L)]/A B) (ρ0)/(2A) C) [(ρ0)(L)]/(2A) D) [2(ρ0)(L^2)]/A E)...

Homework Statement To a source of current, one by one are added 2 resistances, first R1=1ohm, then R2=4ohm. In both cases, in the same period of time (t=t1=t2), the resistors give the same amount of heat (Q=Q1=Q2). Determine the internal resistance ("r" small r) of the electric source...

I'm trying to measure the resistivity of a sample of A356 to back out the thermal conductivity. I do not have anything sensitive enough to measure the micro-ohm resistance (my sample is 0.5" x 0.25" x 3"). If I want to use an oscilloscope or multimeter to measure the voltage drop, I should...

Bonjour, I need to numerically compute the net electrical resistance of a given geometry. I know the shape of my object, it is relatively simple. It's close to this: http://2.imimg.com/data2/QX/UC/IMFCP-3019296/i-shape-big-1-250x250.jpg Actually my shape is even simpler because it's a...

1) A thermistor is connected through a switch to a 12V power supply of negligible internal resistance. When the switch is closed, the initial current in the circuiy is 14mA. A few minutes later it has risen to a constant 20mA. Does the thermistor dissipate more power initially, or after it...

The resistivity of Aluminium is twice that of copper. However, the density of Aluminium is one-third that of Copper. a) For equal length and resistance, calculate the ratio: mass of aluminium/mass of copperI'm thinking, the density ratio (Al:Cu) is 1:3 ...and the resistivity ratio is 2:1 ...so...

Homework Statement In the figure below, current is set up through a truncated right circular cone of resistivity 898 Ω·m, left radius a = 2.00 mm, right radius b = 2.30 mm, and length L = 1.64 cm. Assume that the current density is uniform across any cross section taken perpendicular to the...

Electric plate has three sections with equal resistivity. Those resistivities combined parallel - water boils per 6 minutes. How much time it will take to boil the same weight and same initial temperature of the water if we will combine resistivities sections like in A and C Thanks very much

Here is a detailed description of my question: http://img829.imageshack.us/img829/3413/physics2.png" Any help would be greatly appreciated. P.S. Diameter of the wire = 0.425mm +/- 0.005mm .

I was looking in my old physics text in connection with another thread and the text said high speed electron collisions and slow speed drift of electrons with an applied electric field don't explain resistivity very well...yielding resistivities 100 times or more than observed. For a plain...

why shouldn't the meissner effect occur in a non conventional zero material?

Given the following data on copper, how do i calculate the resistivity? Relaxation time: 2.50e10-14s Density: 8940Kgm-3 molar mass: 63.5g is there an equation for it.

Hello to everyone. I am a little confused regarding what stands for the designation of [Ohm/m]. Before I used to [Ohm*m] for designation of resistivity (it calls sometimes resistance per unit length). For example I have a wire (copper). The resistivity could be found from the table (17.2...