Resistance calculation Definition and 40 Threads

Thermal resistance is a heat property and a measurement of a temperature difference by which an object or material resists a heat flow. Thermal resistance is the reciprocal of thermal conductance.

(Absolute) thermal resistance R in kelvins per watt (K/W) is a property of a particular component. For example, a characteristic of a heat sink.
Specific thermal resistance or thermal resistivity Rλ in kelvin metres per watt (K⋅m/W), is a material constant.
Thermal insulance has the units square metre kelvin per watt (m2⋅K/W) in SI units or square foot degree Fahrenheit hours per British thermal unit (ft2⋅°F⋅h/Btu) in imperial units. It is the thermal resistance of unit area of a material. In terms of insulation, it is measured by the R-value.

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  1. MrHappyTree

    Resistance in complex geometries

    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...
  2. H

    Resistance calculation -- Comparing coax cable insulator resistances

    Since both cylinders have the same material, this implies the density is the same. Length is also the same based on the question. We only need to compare the radii for resistance. R2 = pi ((2b)^2 - (2a)^2) R1 = pi (b^2 - a^2) R2/R1 = 4, so my answer is C. But, the given answer is A. Where did I...
  3. S

    Finding Equivalent Resistance Using Symmetry and Kirchhoff's Laws

    By the use of symmetry, I have found that equal currents will flow through opposite edges like A-C and C'A', but still, the use of kirchhoffs current and voltage laws lead to four equations in four variables which I am not able to solve, neither I am sure that the four equations which I have...
  4. E

    Electric current and resistance question

    Homework Statement:: problem solving You build a wire by combining an 8 inches copper wire with a 10 inches nichrome wire. If their combine resistance is 10 kΩ, find the cross section area of both wires. The nichrome wire has twice the area of the copper wire. Homework Equations:: I = V/R...
  5. E

    Electric current and resistace problem

    This is a problem I have been strugglying since I don't know if I should work it together or apart I ask my teacher and I don't know if I listened well but he told me to use the combine resistance and substract it with the restistance of the material. You build a wire by combining an 8 inches...
  6. Another

    Resistance of composite material

    Composite materials consist of various components such as moist wood ,how will the internal resistance of this material behave? If I want to study the resistance of composite materials, which topic should I study?
  7. Shivang kohlii

    Why is resistance of similar cases calculated differently?

    Homework Statement 1.In the WE-11 resistance is calculated by integrating and that too by taking length as dr and area as the CSA of the small cylinder .. Shouldn't length be l and area by 2πrdr..? I also don't understand why can't we simply use Dl/A formula , Where A =π((2R)^2 - R^2) 2)...
  8. Safder Aree

    Engineering Finding Internal Resistance through Circuit Analysis

    Homework Statement Given this following circuit: What is the internal resistance of the meter movement ( R_I). This is part of a project I'm doing and I know the equation that gives you the internal resistance in this circuit. $$R_I = \frac{R_sR_p}{R_s - R_p}$$. However, I have no idea how...
  9. NYAME EPHRAIM

    Hi, i need to know if this DAC-op-amp calculation is ok

    Homework Statement Homework EquationsThe Attempt at a Solution
  10. B

    Resistance of a semicircular conductor with a rectangular cross section

    Homework Statement There is a conductor with the square-shaped area. the Radii are r1 , r2 with width b and resistivity ## \rho_R##. Find the resistance R between A and B 2. Homework Equations ##I = \iint_A\vec J \cdot d \vec A## ## \vec J = \kappa \vec E ## ## \vec E = \rho \vec J## ## V =...
  11. T

    Engineering How can I simplify this mixed resistors circuit

    Hi I am to calculate Rab of the circuit and I have no idea on how to approach this problem. It would have been all nice and eaasy if it weren't for the vertival 30 ohm resistor. Because of this I'm in a dark spot. I will appreciate any help.
  12. V

    Total Resistance of Parallel Circuit Calculation

    Homework Statement R1= 9 Ohms R2= 17 Ohms R3= 18 Ohms what is the total resistance of this arrangement? Express answer in ohms, correct to one decimal place. Homework Equations I used the Parallel circuit formula 1/r1 + r2 + r3 The Attempt at a Solution I got 4.0 Ohms, apparently, it is...
  13. Ali Zain

    Rank in order, from largest to smallest, the resistance (eq)

    Homework Statement There is a figure, I'll try my best to draw/describe. 1. All three resisters are in parallel ___R____ !___R____! !___R____ ! 2. 2 resisters are parallel and one in series, after the parallel (ignore the dots) ___R___ ... _____R___ !___R___ ! 3. 2...
  14. J

    Limiting amps and volts from a battery

    I have a project that involves a small motor, and the battery powering it would blow the motor in an instant without proper use of resistors. The battery I'm using is rated at 9.6 volts and 1600ma. The motor however, is rated at 3 volts and 0.3 Amps. I would like to go just under these ratings...
  15. H

    A How is the von Klitzing constant used to measure resistance?

    How is the constant used to measure resistance? I can't find a clear answer anywhere. The constant is h/e^2 but that doesn't really help in seeing how it is linked to resistance other than the units being the same in base units.
  16. R

    Resistance calculation on right angle current flow

    As you know, resistance of a rectangular shape is given by R=ρ A/L But how do we theoretically calculate the resistance of the bottom case? ( now, the current flow is not parrallel, current flows from bottom through the right side) I would like to know if there is any references for this...
  17. moenste

    How Do You Calculate the Resistance of a Voltmeter?

    Homework Statement A battery is known to have an EMF of 5.0 V but when a certain voltmeter is connected to it the reading is 4.9 V. The battery can deliver a current of 0.40 A when connected to a resistance of 12 Ω. What is the resistance of the voltmeter? Answer: 24.5 Ω. 2. The attempt at a...
  18. Adeel Ahmad

    Electricity, finding voltage and resistance

    Homework Statement Design a voltage divider circuit to provide an output voltage v0 = 5V from a 12V source. The current taken from the 12V source is to be 100mA. a)Find the values of R1 and R2. b)Now suppose a load resistance of 200 ohms is connected across the output terminals (in parallel...
  19. R

    Equivalent resistance of pentagon of resistors

    Homework Statement Here: http://imgur.com/a/5rRgu 2. Homework Equations V=IR The Attempt at a Solution Basically from reversing the polarity of the cell and looking at a mirror image of the circuit i got the following relationships. First I(9)=0 then I(1)=-I(4) I(5)=-I(6) I(7)=-I(8). I...
  20. R

    Hard Circuit simplification problem

    Homework Statement Everything is in the picture. Question 3(a) This is for preparation for a contest. http://i.imgur.com/FtiKaYw.jpg Homework Equations V=IR The Attempt at a Solution I calculated the total resistance of the first circuit and used that to evaluate V(AB). But this is in...
  21. V

    Resistance Between Two Rectangular Electrodes

    Hello everyone. I have what is probably a relatively simple question. I'm trying to calculate the resistance between two rectangular copper plates submerged in water. I found this thread that briefly discusses it...
  22. Swapnil Das

    Method of Symmetry for Equivalent Resistances

    I have been studying the method of symmetry from some days, which essentially reduce the effort needed for the evaluation of equivalent resistances. My textbook states: Points having symmetrically located about initial and final points have the same potentials.So, the resistances between these...
  23. L

    Meter Bridge: Finding Error in Resistance

    Homework Statement Homework Equations How to find error in resistance ? The Attempt at a Solution I found out the resistance without error. But What is the way to figure out an error of an instrument ?
  24. A

    Calculate the rise in temp in copper 3 core wire

    Dear Guys, It will be really helpful if some one can give me the calculation step by step or some calculator where in I can resolve my long pending problem. Thanks in advance I will be really glad to have a correct answer. The Q is below Calculate temperature rise in 3 core cable after 3 hrs...
  25. A

    Find the equivalent resistance between AB

    Homework Statement Find the equivalent resistance between AB. Homework EquationsThe Attempt at a Solution I could not find any Wheatstone bridge or series parallel combination. Should I use star delta transformation ? If yes, how exactly should I use it ?
  26. N

    Engineering Linear potentiometer in a circuit problem

    Homework Statement The total resistance for the linear potentiometer (R1) is 470 Ohms, and its length is 50mm. Calculate the distance x of the slider from the left edge of the potentiometer for which the output voltage (V out) is 0 V. Homework Equations Vout = Vin * (R1/(R2+R1)) The Attempt...
  27. A

    Calculating Resistivity across a mesh sheet

    Hi everyone! I'm trying to figure out how to go about this in calculating resistivity of a titanium grade 1 mesh. From what I know the ρ for titanium is 4.3x10^-8 ohm x m. The mesh will be a 1x12inch sheet wrapped cylindrically end to end. Here are the stock values including a change in area...
  28. J

    Resistance Calculation in Radial Direction - Learn Formula

    Hi, I am wondering how to calculate the resistance for the current running in radial direction starting from the center of a circle? It seems there is a formula out there, and I would also like to know how to derive that formula..Thanks.
  29. Sanchayan

    Can Kirchoff's Laws Be Applied to Solve Hexagonal Grid Resistance?

    https://brilliant.org/problems/hexagonal-grid/ I've been pondering on this but not being able to solve.I mean applying Kirchoff's law here is of no use. Any ideas?
  30. M

    Need to calculate the resistance accross membrane in water

    Hello everybody, I am chemist. and I prepare ionic membrane and placed in a home made acrylic cell containing 0.1M NaCl separated into two portions by ionic membrane. I applied DC voltage of 9.6V (using 9V battery). Using multi-meter the measured DC voltage in water was 4.45V. The distance...
  31. A

    Wire rope and pulley sheave resistance calculation

    Hi, this is my first posting on this forum in the hope someone could assist me with a calculation. I have read several threads which I think partly covers my problem but to be honest the example answers given are way beyond my comprehension. Basically I need to raise a platform which runs...
  32. G

    Calculating Cable Resistance for Internal Temperature

    Hi. I am a bit confused about the formula for cable resistance. It is quite a long question but I got stuck at this point. I have found the resistance Rdc@20 degrees but I need to adjust it for "internal working temp" of 60 degrees. The formula I have found gives compensation for changes in...
  33. K

    A strange electrical circuit - resistance calculation

    Hello. So I've got an electrical circuit on page 4 of this: http://www.iuventa.sk/files/documents/2_olympiady/fo/54.%20rocnik%202012-2013/ulohy%20a%20riesenia/skolske%20kolo/f54skcul13.pdf and I am to calculate the total resistance of the circuit, but I have no idea on how to solve that strange...
  34. P

    Temperature coefficient of resistance calculation

    When we are supposed to calculate the value of "temperature coefficient of resistance " i.e. α , how are we supposed to choose between the following two formulae : α = (R2 - R1) / (R1*T2 - R2* T1 ) or α = (R2 - R1)/ [ R1 *( T2-T1) ] I have attached scanned pictures of two similar...
  35. R

    Resistance calculation of odd-shaped plate

    Hello If the resistivity rho and the dimensions are known, any schoolboy can calculate the end-to-end resistance of a strip of metal. But how do you do it if the strip is not regular as in the image?
  36. C

    Resistance calculation in a cube

    Homework Statement each edge of a cube is built with a one ohm resistor, body diagonals are also built with one ohm resistors each. find out equivalent resistance across any two adjacent vertices. Homework Equations i guess it deals with star and delta transformations The Attempt at...
  37. L

    Earthing resistance calculation

    Hi! I'm interested if there is any free software on the web for the calculation of resistance of complex earthing consisting of several interconnected loops? Thanks!
  38. V

    How Much Torque is Needed to Overcome an Obstacle with a Rotating Wheel?

    Hi to all Please help me to clarify this situation: There is a rotated wheel on a plan surface. What torque/power will be necessary to spring an obstacle with a concrete height. For ex. here are some data: 1.Wheel mass 10 kg 2.Wheel radius 0,3 m 3.Rotation speed 100 RPM 4.Obstacle...
  39. T

    Redrawing Circuit for Equivalent Resistance Calculation

    Just a simple question how would i redraw this circuit so that i could find the equivalent resistance? (circuit image attached) thanx in advance
  40. O

    Does Air Resistance Increase with Speed Due to Collisions with Air Particles?

    I'm doing a data handling course work project. I've calculated various values for resistance and found that resistance increases as the speed of the body increases. I know that as the body is rolling very little of the force is friction, so most of it will be air resistance. i have an idea...
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