الفيزياء العامة الجزء الثاني#موقع الفيزياء.كوم

Current & Resistance
7.9 Problems
7.1) A current of 5A exists in a 10 Ω
resistor for 4min. (a) How many
coulombs, and (b) how many
electrons pass through any cross
section of the resistor in this time?
7.2) A small but measurable current
of 1.0 ×10 -10 A exists in a copper
wire whose diameter is 0.10in.
Calculate the electron drift speed.
7.3) A square aluminum rod is 1.0m
long and 5.0mm on edge. (a) What
is the resistance between its ends?
(b) What must be the diameter of a
circular 1.0m copper rod if its
resistance is to be the same?
7.4) A conductor of uniform radius
1.2cm carries a current of 3A
produced by an electric field of
120V/m. What is the resistivity of
the material?
7.5) If the current density in a
copper wire is equal to
5.8×10 6 A/m 2 , calculate the drift
velocity of the free electrons in this
wire.
7.6) A 2.4m length of wire that is
0.031cm 2 in cross section has a
measured resistance of 0.24Ω.
Calculate the conductivity of the
material.
7.7) Aluminium and copper wires of
equal length are found to have the
same resistance. What is the ratio
of their radii?
7.8) What is the resistance of a
device that operates with a current
of 7A when the applied voltage is
110V?
7.9) A copper wire and an iron wire
of the same length have the same
potential difference applied to
them. (a) What must be the ratio of
their radii if the current is to be the
same? (b) Can the current density
be made the same by suitable
choices of the radii?
7.10) A 0.9V potential difference is
maintained across a 1.5m length of
tungsten wire that has a crosssectional
area of 0.6mm 2 . What is
the current in the wire?
7.11) A wire with a resistance of
6.0Ω is drawn out through a die so
that its new length is three times its
original length. Find the resistance
of the longer wire, assuming that
the resistivity and density of the
material are not changed during the
drawing process.
7.12) A wire of Nichrome (a nickelchromium
alloy commonly used in
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