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physics!!!!!!!!!!!!!!!!!!!!!!!

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halosh92:
when a potential difference V is applied between the ends of a wire of diameter "d" and length "l", the current in the wire is 'I"
what is the current when a potential difference of 2V is applied between the ends of a wire of the same
material of diameter 2d and the length "2l" ? assume that the temperature of the wire remains constant?
a) I
b) 2I
c) 4I
d) 8I
???

vanibharutham:
Using the idea of Resistivity (NOT RESISTANCE)

The following will stay constant between the two different wires:

1) Resistivity, p, which is an intrinsic property of the materials and is a measure of the resistance of 1m³ of a substance.

Anyways:

R = p L / A
( R = resistance, p = resistivity, L = length, A = cross sectional area)

For first wire:

R = 4 p L / pi d²

V = I R

I = V pi d² / 4 p L


For second wire:

R = 2 p L / pi d²

x I = 2V pi d² / p L

x = 8

Therefore d)

halosh92:
thankyou

two wires made of the same material and of the same length are connected in  parallel to the same voltage supply  wire P has a diameter of 2mm. wire Q has a diameter of 1mm
whats is the ratio current in P/current  in Q
a) 1/4
b) 1/2
c) 2
d) 4

astarmathsandphysics:
a cos R pl/A=pl/pi(d/2)2 so if d is double the current is halved

halosh92:
just a few random questions:
 1) a beam, the weight of which maybe neglected , is supported by three identical springs. when a weight W is hung
from the middle of the beam, the extensionj of each spring is X
the middle spring is then removed and the weight is removed .
what is the extension when a weight of 2W is hung from the middle of the beam
a) 3X/2
b) 4X/3
c)2X
c)3X



2) two solid substances P and Q have atoms of masses Mp and Mq respectively.
they have Np and Nq atoms per unit volume
it is found by experiment that the density of P is greater than that of Q
which one is the correct one?
a) Mp>Mq
b)Np>Nq
c)MpNp>MqNq
d)Mp/Np   >    Mq/Nq



3) what is the evidence for the molecules in solids and liquids having approximately the same separation??




4) a hard ball and a soft ball with equal masses and volumes are thrown at a glass window the ball hits the window at the same speed . suggest why the hard ball is more likely than the soft ball break the window?


thx alottttt

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