Capacitance and Electromagnetism

[Coldsoul]

1.Suppose that a blood vessel is 2.5 mm in diameter, the magnetic field is 0.08 T, and the electromagnetic force is 0.10 mV. What is the velocity flow of the blood? Assume that blood carries charged ions.

Homework Equations

B=F/qvattempt
looking for v isn't possible since I have no idea how to look for q, it says q is the charge of the moving particle along a constant magnetic field... or am I using inappropriate equation? P.S. Sorry for posting two problems in one post, I have already figured out the first one. Sorry for not posting any attempt, I was expecting something like people would also post their answers and I will compare my answers later, I thought it would work the that way, my apologies.

 

[gneill]

Hi Coldsoul, welcome to Physics Forums.

You've posted two problems (in one post) and not supplied your attempt at solution for either one, or even your thoughts on what might be involved in attacking the solutions. If we are to help, we need to see what you've tried.

 

[gneill]

1.Suppose that a blood vessel is 2.5 mm in diameter, the magnetic field is 0.08 T, and the electromagnetic force is 0.10 mV. What is the velocity flow of the blood? Assume that blood carries charged ions.

Homework Equations

B=F/qv


attempt
looking for v isn't possible since I have no idea how to look for q, it says q is the charge of the moving particle along a constant magnetic field... or am I using inappropriate equation?


P.S. Sorry for posting two problems in one post, I have already figured out the first one. Sorry for not posting any attempt, I was expecting something like people would also post their answers and I will compare my answers later, I thought it would work the that way, my apologies.

No problem. You'll soon get the hang of it.

Would, by any chance, this problem have come from a section of your course where you are learning about the Hall Effect? To me it just "has that sort of feel" to it.

If so, you might benefit by looking at some material on the Hall Effect. This http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/hall.html" has a pretty good summary of the relevant bits. Pay particular attention to the part where it shows how the drift velocity is related to the current and conductor cross sectional area.

 

[Coldsoul]

The hall effect is similar to the relevant equation I posted since the hall effect assumed that the moving charges are electrons. Therefore, the drift velocity was talking to velocity of the density of moving electrons.

relevant equations:
B=F/qv, looking for F, we have F=qvB
Hall effect: F = eVdB; where e=charge density of the electrons, Vd= drift velocity and B= magnetic field

similar isn't it? still can't find the velocity... what bothers me is the diameter of the vessel, I am looking at the surface charge density but it doesn't seem like related to it.

I really appreciate your reply, thanks. ^^

 

[gneill]

The Hall Effect works for positive or negative charges.

You're given a magnetic field, a "conductor" diameter, and a potential difference, presumably across the diameter of the conductor. Sounds like Hall Effect to me.

Instead of looking at the force expressions, look at the Hall voltage:

$$V_H = \frac{I B}{n \; q \; d}$$
and at the current as a function of charge density and drift velocity:
$$I = n \; q \; A \; v$$

A little algebra and you're done.

 

[Coldsoul]

now I see, thanks much...

next, can you teach me how to post equations like you do?

 

[gneill]

There's an introduction to using latex to embed equations here:

https://www.physicsforums.com/showthread.php?t=8997