# questions in physics

• Jan 4th 2011, 07:59 AM
r-soy
questions in physics
questions :

1 ) A person notices a mild shock if the current along a path through the thumb and index finger exceeds 78 ľA.?
Compare the maximum possible voltage without shock across the thumb and index finger with a dry-skin resistance of 4.0 X 10^5 and a wet-skin resistance of 2500 . wet skin? dry skin?

Given :
Current = 78 ľA convert (78 X 10^-6)
dry-skin resistance of 4.0 X 10^5
a wet-skin resistance of 2500

For dry-skin
V=IR = (78 X 10^-6) X (4.0 X 10^5 ) = 31.2 volts
For a wet-skin (78 X 10^-6) X (2500 ) = 0.195 volts
the dry-skin more voltge

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2 )

Suppose that you wish to fabricate a uniform wire out of 0.850 g of copper. Assume the wire has a resistance R = 0.500 , and all of the copper is used.
(a) What will be the length of the wire? in meters
(b) What will be the diameter of the wire? in micrometers
resistivity depen on Area and lentgh and resistance
then :
a) R = pl/A
b)?
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3)
Calculate the diameter of a 1.7 cm length of tungsten filament in a small lightbulb if its resistance is 0.050?R = P x L / A (P is a constant )
A= P x L/ R=(5.6 x 10-8)(0.017)/0.050
=1.904X10^8 cm^2

Now How I find the dimeter ?

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4) A potential difference of 12 V is found to produce a current of 0.44 A in a 3.5 m length of wire with a uniform radius of 0.38 cm. Find the following values for the wire.
a) the resistance

b) the resitivity

Given
v = 12
current = 0.44 A
l= 3.5
A = 0.38
a) the resistance
R= V/I = 12 / 3.5 = 3.42 ohms

B ) the resitivity
r = pl/A
p =l/RA
=3.5/3.42X0.38 = 2.6 Jule ...
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5 )
A rectangular block of copper has sides of length 10 cm, 20 cm, and 40 cm. If the block is connected to a 6.0-V source across opposite faces of the rectangular block, what are (a) the maximum current and (b) minimum current that can be carried?( How I dolve this Q )
• Jan 4th 2011, 09:08 AM
rtblue