17: Equations

Question 1

Stoke’s Law: F =

Answer 1

F = 6πνrv
ν (nu) = viscosity of the fluid
r = radius of the object
v = velocity of the object

Question 2

Millikan’s oil drop experiment:
Before the field is switched on
When the drop reaches terminal velocity, 2 forces are equal…

Answer 2

mg = 6πνrv

Question 3

Millikan’s oil drop experiment:

Mass of drop:

Answer 3

4πr³ρ/3

volume * density ρ

Question 4

Millikan's oil drop experiment:
Equate weight (w/ mass of 4πr³ρ/3) with viscous force.
Rearrange to find r

Answer 4

4πr³ρg/3 = 6πνrv
Remember the g for weight!!
so r² = 9νv/2ρg

Question 5

Millikan’s oil drop experiment:
After field is switched on
Which forces are equal

Answer 5

qV/d = mg = 4πr³ρg/3

Question 6

Millikan’s oil drop experiment:

Force exerted on a current carrying wire

Answer 6

F = BIl
B = magnetic flux density
I = current
l = length (m)

Question 7

Combine I = q/t and v = l/t to get a new equation for current

Answer 7

I (current) = qv/l
v = velocity of charged particle
q = charge
l = length

Question 8

For a charged particle travelling in a circular path, which 2 forces are equal….
Rearrange to give r =

Answer 8

qvB = mv²/r

r = mv/qB