Electromagnetic Forces and Fields: Ranking, Ratio, and Distance Calculations

[nautica]

11) the diagram shows 3 equally spaced wires that are perpendicular to the page. the currents are equal, 2 being out of the page and 1 going into the page. rank the wires according to the magnetude of the forces on them, from least to greatest.


. x .
1 2 3

12) A proton (charge e) traveling perpendicular to a mag field, experiences the same force as an alpha particle (charge 2e) which is also traveling perpendicular to the same field. the ratio of their speeds, v (proton) / v (alpha)

My answer is 2

13) the mag field in T a distance of 2 cm from a long straight wire carrying a current of 2 A is about

15) 2 long parallel straight wires carry equal currents in opposite directions. At a point midway between the wires, the mag field they produce is?

a) zero ( I picked a)
b) non-zero and along a line connecting the wires
c) non-zero and parallel to the wires
d) non-zero and perpendicular to the plane of the two wires
e) non of the above

16) 2 long strait wires are parallel and carry current in the same direction. the currents are 8 A and 12 A and the wires are separated by .4 cm. the mag field in tesla at a point midway between the wires is?

18) the mag field outside a long straight current-carrying wire depends on the distance R from the wire axis according to
a) R
b) 1/R
C) 1/R^2
d) 1/R^3
e) 1/R^3/2

 

[Doc Al]

Field from a current-carrying wire: Learn it!

Originally posted by nautica
11) the diagram shows 3 equally spaced wires that are perpendicular to the page. the currents are equal, 2 being out of the page and 1 going into the page. rank the wires according to the magnetude of the forces on them, from least to greatest.


. x .
1 2 3

No. First note the symmetry between the left and right wires: they must experience the same force. Now find the B field that they exert on the middle wire.

12) ...
My answer is 2

OK.

13) the mag field in T a distance of 2 cm from a long straight wire carrying a current of 2 A is about

Learn the expression for the field produced by a current carrying wire; look it up.

15) 2 long parallel straight wires carry equal currents in opposite directions. At a point midway between the wires, the mag field they produce is?

a) zero ( I picked a)
b) non-zero and along a line connecting the wires
c) non-zero and parallel to the wires
d) non-zero and perpendicular to the plane of the two wires
e) non of the above

No. Once again, you must know the field produced by a current-carrying wire. No calculation is needed here, but you do need to know what direction the field points. Compare with #11

16) 2 long strait wires are parallel and carry current in the same direction. the currents are 8 A and 12 A and the wires are separated by .4 cm. the mag field in tesla at a point midway between the wires is?

Same comment.

18) the mag field outside a long straight current-carrying wire depends on the distance R from the wire axis according to
a) R
b) 1/R
C) 1/R^2
d) 1/R^3
e) 1/R^3/2

Ditto.

 

[nautica]

On #18

B= uI/2pieR

So the answer should be 1/R. Right?

Nautica

 

[nautica]

I am confused about this one.

15) 2 long parallel straight wires carry equal currents in opposite directions. At a point midway between the wires, the mag field they produce is?

a) zero
b) non-zero and along a line connecting the wires
c) non-zero and parallel to the wires
d) non-zero and perpendicular to the plane of the two wires
e) non of the above

 

[nautica]

On #11 the 1,2,3 were the names of the wires. I forgot to include my answer

2 would have the greatest and 1 and 3 would be tied. right?

 

[himanshu121]

Originally posted by nautica
I am confused about this one.

15) 2 long parallel straight wires carry equal currents in opposite directions. At a point midway between the wires, the mag field they produce is?

a) zero
b) non-zero and along a line connecting the wires
c) non-zero and parallel to the wires
d) non-zero and perpendicular to the plane of the two wires
e) non of the above

d