a) 2

b) 4

c) 8

d) 16

e) 32

need explanation of equation please?

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a) 2

b) 4

c) 8

d) 16

e) 32

need explanation of equation please?

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·
590 Posts

Poiseulle's law isI thought Poiseulle Law is talking about resistance not flow, Can we apply it to flow?

and Flow = ΔP/resistance

so the factor of change in ΔP (1/r^4 in this case) is the same as that in Flow, by the transitivity of multiplication.

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590 Posts

Okay, I said that badly...Poiseulle's law is

andFlow = ΔP/resistance, by the transitivity of multiplication.

so the factor of change in ΔP (1/r^4 in this case) is the same as that in Flow

The italicized part should say "Flow is Q in the equation, so the factor of change in Flow is the inverse of that in ΔP (1/r^4 in this case) = r^4 = 1/16. So, as aktorque said, the flow would decrease by a factor of 16."

Hope that's clearer, and sorry for the bad explanation before!

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590 Posts

This is really the gist, and all we really need to know about Poiseuille's equation. Flow is directly proportional to radius^4, and resistance is inversely proportional to radius^4.Rearranging for Q, you can see that.Q = (blahblahblah) r^4

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88 Posts

Resistance = (8 x viscosity x length)/ radius^4

Resistance = Pressure change/Flow

If radius reduces by 1/2, then resistance increases by 16. (inverse proportnl)

If resistance increases by 16,then Flow reduces by 16.(inversely proportional)

for questions like this, Goljan said, just remember '16', the boards wont go beyond that.

hope this helps.

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