of the same length and same area of cross-section as that of the first nichrome wire [marked ( )]. Note the value of the current. Notice the difference in the current in all cases. Does the current depend on the length of the conductor?
Does the current depend on the area of cross-section of the wire used? have very low resistivity in the range of – Ω m to – Ω m. They are good conductors of electricity. Insulators like rubber and glass have resistivity of the order of to Ω m.
Both the resistance and resistivity of a material vary with temperature. Table . reveals that the resistivity of an alloy is generally higher than that of its constituent metals. Alloys do not oxidise (burn) readily at high temperatures.
For this reason, they are commonly used in electrical heating devices, like electric iron, toasters etc. Tungsten is used almost exclusively for filaments of electric bulbs, whereas copper and aluminium are generally used for electrical transmission lines. Table . Electrical resistivity * of some substances at °C Material Resistivity ( ΩΩΩΩΩ m) Conductors Silver .
× – Alloys Constantan × – (alloy of Cu and Ni) Manganin × – (alloy of Cu, Mn and Ni) Nichrome × – (alloy of Ni, Cr, Mn and Fe) Insulators Glass – Hard rubber – Ebonite – Diamond - Paper (dry) * You need not memorise these values. You can use these values for solving numerical problems. Example . (a) How much current will an electric bulb draw from a V source, if the resistance of the bulb filament is Ω ?
(b) How much current will an electric heater coil