# Homework Help: Several mixed assignments

1. May 3, 2015

Hi! Iam trying to get back to studying after several years of working, and currently Iam trying to higher my grades so I can make it to engineering college.. I would be grateful if you guys could help me with these assignments and check if I have done it right, because I really want an A.

ASSIGNMENT 1
1. The problem statement, all variables and given/known data
Currents are equal in the two long straight parallel conductor but flowing in the opposite directions. The distance between the conductors is 10 cm. Magnetic field size at a point midway between the leaders is 80 microT, apart from the Earth's magnetic field.

a, How big is the current in the conductors?
b, Calculate the force on every meter of one of the conductors

2. Relevant equations
a, B=k*I/a
b, F=B*I*l

3. The attempt at a solution
a=10cm
B=80*10^-6 T
l=?
k=8,99*10^9
I=(B/k)*a

l=1m
B=80*10^-6 T
I=from a
F=(80*10^-6)*1*I(from a)

ASSIGNMENT 2
When a negatively charged particle is moved from the bottom plate to the top plate in a homogenous electric field 2,9*10^-8 J is being transformed to potential energy. Is the top or the bottom plate positively charged? How big is the charge of the particle? Current between the plates is 100V.

W=q*U --> q=W/U

ASSIGNMENT 3
A electron passes through a vertical magnetic field like the figure shows. The path is in a horisontal plane.
a, Give the motion direction in the path.
b, The electrons velocity is constant under the whole passage through the field, explain this!

No equations

My exp;
a, The force will point to the "middle" of the circular motion that occurs. The force is perpendicular to the motion, and the electrons motion is directed to the currents.

b, F is perpendicular to the motion, the velocity remains therefore constant because the electrons kinetic energy does not change.

ASSIGNMENT 4
Look at the figure, which force acts on a positive charged proton in the point P?

Equations:
F=k*(q1*q2)/r^2

Fres=F1+F2

Solution tried
F1=8,99*10^9*(1,602*10^-14)*(1,9*10^-9)/(0,03)^2

F2=8,99*10^9*(1,602*10^-14)*(6,2*10^-9)/(0,02)^2

Fres=? Iam not sure how to keep on going here...

ASSIGNMENT 5
On which distance from a long straight conductor with the current 25 A, is the magnetic field=earth magnetic field, 47 microT?

Equations:
B=k*I/a

k=8,99*10^9
I=2,5 A
a=?
B=47*10^-6 T

Solution:
Solve for a.

Thank you a lot! As you see Ive tried to solve most of it, would be grateful if anyone could go through them and see if anything is wrong, and tell me it so I can learn!

2. May 3, 2015

### SteamKing

Staff Emeritus