Exercise 7 - Conductivity

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Exercise 7 - Conductivity
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a) The current density across a cylindrical conductor of radius R varies according to the equation j = jo(1 - r/R)
where r is the distance from the axis. Thus the current density is a maximum jo at the axis r = 0 and decreases linearly
to zero at the surface r = R. Calculate the current in terms of jo and the conductor's cross-sectional area A = pR2. (b)
Suppose that instead the current density is a maximum jo at the surface and decreases linearly to zero at the axis
(center) so that j = jo r/R. Calculate the current again. Why is this result different from that in (a)?
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When a potential difference of 115 V is applied between the ends of a 9.66-m-long wire, the current density is J =
1.42 A/cm2. Calculate the conductivity of the wire material.
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‫מוליכים וקבלים‬
‫ אם שיפוע הקונוס‬.‫ היא ההתנגדות הסגולית‬ρ -‫ ו‬,‫ הוא הגובה‬L ,‫ הם רדיוסי הבסיס בהתאמה‬b-‫ ו‬a.‫נתון נגד בצורת קונוס קטום כמתואר באיור‬
(!‫ נוכל להניח כי צפיפות הזרם בין בסיסי הנגד היא קבועה לרוחב כל שטח חתך לאורך הנגד )אבל לא בניהם‬,‫הוא קטן‬
‫י את ההתנגדות של הנגד הנ" ל‬/‫א( חשב‬
.a=b ‫עבור המקרה הפרטי של‬
-‫י כי התשובה מצטמצמת ל‬/‫ב( הראה‬
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Current
The space between two concentric spheres,
is filled with a conductor with the resistivity .
What is the resistance between the inner and outer surfaces.
Answer:
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Current
There are three electric light bulbs for the voltage 110 V and power 50 W, 50 W, and 100 W.
How can they be connected to 220 V to use the whole power of each one ? (Draw the circuit.)
http://physweb.bgu.ac.il/COURSES/PHYSICS2_BuildEng/ClassEx/class7.php
24/06/2008