Compute lorentz force from charge

[tifa8]

Homework Statement

A raindrop carrying a charge of 25x10^-12 coulombs falls at a velocity of 5 m/s between the poles of a permanent magnet. It passes through a 50 mm long region in which the magnetic field density of 0.9 T is directed horizontally.

1) determine the lorentz force of the raindrop
2) ESTIMATE THE HORIZONTAL COMPONENT OF THE RAINDROP VELOCITY AFTER IT PASSES THROUGH THE MAGNETIC FIELD (DIAMETER DROP=1MM)

Joined, diagram of how i interpreted the text

Homework Equations

F=q*(vector v x vector B)=qvb in magnitude

The Attempt at a Solution

1) by applying the formula I got F=25.10^-2*5*0.9=1.125 N

However I do not understand question 2. For me the horizontal velocity component is equal to zero (going down) so it doesn't make sense to me.

Can someone explain it to me ? Thanks

 

[tifa8]

sorry F=1.125.10-10

 

[vela]

Won't the force cause the drop to accelerate? What will happen to its velocity?

 

[tifa8]

the velocity will increase and change slightly direction i think. But even though there is not any horizontal component , right ? I really cannot see it...

 

[vela]

Try drawing it from the point of view where the magnetic field points into or out of the page. Which way does the force point?

 

[I like Serena]

Hi tifa8!

The raindrop is accelerated horizontally by the Lorentz Force F.
To find the horizontal acceleration you need to estimate the mass of the raindrop (F=ma).
To find the horizontal component of the velocity you need to calculate the time the magnetic field exerts its influence (v=at).

 

[tifa8]

Oh ok thanks. Now I can visualize the problem. Thank you I like serena and vela :)