As the temperature of a metal, for example copper, is lowered the resistivity ac

Question

As the temperature of a metal, for example copper, is lowered the resistivity actually decreases. As the temperature of a nonmetal, for example a ceramic material, is lowered the resistivity actually decrees. If a piece of silicon is "doped" with the appropriate element it becomes useless and is referred to as "dopey" material. A superconductor is a material that loses its electrical resistance below a certain temperature referred to as the critical temperature. If a small amount of certain elements is added to an insulating material the electrical properties of insulating material may be changed significantly. Use the figure at the right to answer questions 11 and 12. R_1 = 19 k Ohm, R_2 = 39 k Ohm, R_3 = 29 k Ohm, and C = 1800 mu F, epsilon = 17 kV. Assume that the capacitor is completely uncharged before switch S is closed. Circle the letter(s) corresponding to the TRUE statement(s) below. Statements: A long time after the switch is closed the current in R_3 is at a maximum value. A long time after the switch is closed the current in R_2 is exactly the same as the current in R_1. Immediately after the switch S is closed, the capacitor behaves as if there is a "wire connection (i.e., a short circuit)" in the branch between points alpha and beta. Referring to the circuit, "a long time after the switch S is closed" means that more than 30 minutes must pass after the switch is closed. Immediately after the switch S is closed the capacitor behaves as if the lower end of R_2 is left unconnected from the circuit. Switch S has been closed for a very long time. It is then opened and C discharges. How long after S is opened before C can be considered to be completely discharged? 350 s. 450 s. 512 s. 612 s. 735 s. Determine the force (magnitude mid direction) on a particle that consists of three protons and three neutrons which is traveling at a speed of 3.00 times 10^6 m/s in the +x axis direction. The particle suddenly enters a uniform 1.5 T magnetic field that is oriented in the plane of the paper, at 15.6 degrees counter clockwise with respect to the +x-axis. 0.50 pN, out of the paper. 0.54 pN, out of the paper. 0.58 pN, out of the paper. 0.62 pN, into the paper. 0.65 pN, into the paper. The figure at the right represents two coaxial metal spheres of radii k and l with k

Explanation / Answer

Statement A: As the temperature of a metal (for example copper) is lowered, the resistivity actually decreases,

Since the electrical resistivity of a conductor such as copper wire is dependent upon the collisional processes within the wire, the resistance could be expected to increase with temperature since there will be more collisions.

The variation of resistivity with temperature is expressed as

                                  = o [1+o (T-To)]

From the above equation, resistivity varies linearly with temperature.

SO the given statement is TRUE.

Statement B: As temperature of nonmetal, for example ceramics, is lowered, the resistivity actually decreases,

In contrast to metals, ceramics have very low electrical conductivity due to Ionic-Covalent Bonding which does not form free electrons.

                                  = oe (Eg/KT)

i.e Resistivity decreases exponentially upon the increment of temperature.

So the given statement is FALSE.

Statement C: If a piece of silicon is doped with the appropriate element, it becomes useless and is referred as dopy materials

Doping of a small percentage of impurity / foreign atoms into the pure/intrinsic semiconductors produces dramatic changes in their electrical properties. The doped materials are referred as Extrinsic semiconductors.

So the given statement is FALSE

Statement D: A superconductor is a material that loses its electrical resistivity below a certain temperature referred as critical temperature.

In superconducting materials, the characteristics of superconductivity appear when the temperature is lowered below a critical temperature. The onset of superconductivity is accompanied by abrupt changes in various physical properties.

According to the Meissner Effect, When a superconductor is placed in a weak external magnetic field H, and cooled below its transition temperature, the magnetic field is ejected.

So the given statement is TRUE

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