The resistance R of a conductor depends on its shape and physical dimensions and a property of the material called the resistivity p What does the resistivity of a material depend upon?  Assuming that the resistivity of copper is a quarter of that of aluminium and that the density of copper is three times that of aluminimium, find the ratio of the masses of copper and aluminium wires with the same length and the same resistance but with different cross - sectional areas .

The Resistance of Nichrome Wire The radius of a piece of Nichrome wire is 0.306 mm. (Assume the wire's temperature is 20°C.) (a) Calculate the résistance per unit length of this wire. SOLUTION Conceptualize This table shows that Nichrome has a resistivity two orders of magnitude larger than the best conductors in the table. Therefore, we expect it to have some special practical applications that the best conductors may not have. Categorize We model the wire as a ---Select--- so that a simple geometric analysis can be applied to find the resistance. Analyze Use this equation and the resistivity of Nichrome to find the resistance per unit length (in 0/m): R 0/m %3D %3D %3D A (b) If a potential difference of 10 V is maintained across a 1.0 m length of the Nichrome wire, what is the current in the wire? SOLUTION Analyze Use this equation to find the current (in A): AV I = %3D A R Finalize Because of its high resistivity and resistance to oxidation, Nichrome is often used for heating…

2. Page > of 3 5. Two long coaxial metal cylinders with radii a and b are separated by material of conductivity o (see figure below). The conductivity is not uniform and changes as = (s)0 where k is a constant. If the two cylinders are kept at a potential difference V, find the resistance R between the cylinders. (s)o Hint: Since the conductivity is a function of position, the charge density in the resistive medium is not zero and E does not go like 1/s. However, since the current I is steady, the same current flows across each eylindrical surface. Instead of using Gauss' Law, find E in terms of I, from Ohm's Law. acer F10 F11

How long is a tungsten wire if it has a diameter of 0.179 x 10-3m and a resistance of 2.63 k2? The resistivity of tungsten is 5.62 x 10-* 2-m. length of the wire:

Two wires have the same length and the same resistance but are made up of different materials. The resistivities of these materials are 1.38 Qm and 3.07 Qm. Obtain the ratio of the smaller cross-sectional area to the greater cross-sectional area. Number i Units

Part (a) I measure the resistance of this wire and find it to be R = 156 Q. What is the resistivity of the material the wire is made out of? p= Problem 7: A particular wire has a length of L = 2.7 m and a circular cross-sectional area of radius r= 1.69 mm. G= sin() cos cotan() asin()) acotan() atan() cosh() tanh() I= sin()) cos() cotan() asin() sinh() atan() acotan cosh() tanh() cotanh() Degrees O Radians B Degrees O Radians Part (b) What is the conductivity of this wire, in inverse Ohms per meter? 0 tan()) π ( acos() E ^^^L sinh() cotanh() g L P Y d h m r tan() π acos() E ^^^^ π E 1 Part (c) Give an expression for the current density in the wire if an electric field E is passing through it. Write this in terms of the resistivity and the other variables in the problem. J= n R ( ^^^ sin() cos() cotan() asin() atan() acotan() cosh() + + 7 8 9 4 5 6 1 2 3 0 END NO BACKSPACE DEL CLEAR Part (d) Calculate the current in the wire, in milliamperes, if the field strength is 5.28 V/m. - END NO…

A common 16 gauge medium duty extension cord -- the orange ones that you often see -- contains three copper wires each with a diameter of 1.29 mm.  How much resistance would 15.2 meters of cord add to an appliance that you are using?  The black and white conductors actually carry the current; the third ground wire is just a backup for the white wire.  Use Google or the Resistance PowerPoint show to find the resistivity of copper. Express your answer in normal notation to three significant figures.