Calculate the current in the coil

[mba444]

Homework Statement

A circular coil of 394 turns and area 0.78 m2
is in a uniform magnetic field of 0.8 T. The
maximum torque exerted on the coil by the
field is 0.0059 N · m.
Calculate the current in the coil. Answer in
units of A

Homework Equations

torque= i*A*B

The Attempt at a Solution

what i did is that i solved for the current using the above equation i= torque/(A*B) but i keep getting the wrong answer .. i think because of the number of turns but i don't know were to include it

i need ur help thanks in advance

 

[Doc Al]

Torque = μ X B, where μ = nIA.

 

[mba444]

so is it
i = torque /(number of turns *A*B)

 

[Doc Al]

so is it
i = torque /(number of turns *A*B)

Yes.

 

[mba444]

Assume the 394 turns of wire are used to form
a single-turn coil with the same shape but
much larger area.
What is the current if the maximum torque
exerted on the coil by the field is 0.0059 N · m?


this a second part of the question but i really didnt understand the difference

 

[Doc Al]

You need to figure out the area of this larger coil. Hint: What's the length of the wire?

 

[mba444]

i tried to figure out the length where i came up with this equation but still i couldn't figure what to put for the F

length = F/(i*B)

im kind of lost

 

[Doc Al]

Figuring out the length of the wire is a geometry problem. You had a coil of a given area and number of turns. What was the circumference of that coil?

 

[mba444]

C= 2*pi*r

 

[Doc Al]

C= 2*pi*r

Good. Use the known area to find the radius.

 

[mba444]

ok i did so know
1 loop = 2*pi*r (i just found)
394= X
so do i do the cross multiplication to solve for X which is the new area

 

[Doc Al]

ok i did so know
1 loop = 2*pi*r (i just found)
394= X
so do i do the cross multiplication to solve for X which is the new area

Do this:
Use the area of the original coil to solve for the radius, using A = pi*r².
Use the radius to find the length of each loop, using the circumference formula.
Find the total length of the wire by multiplying the length of each loop by the number of loops.
That becomes your new circumference of your big coil. Work backwards to find, its radius then area.

 

[mba444]

ok thanks a lot i got it know .. sorry if i wasted your time

 

[mba444]

i got for the larger area = 121084 m^2

i plugged in this eqs i = (.0059)/(394*121084*0.8)

but i got the wrong answer =(

 

[Doc Al]

i got for the larger area = 121084 m^2

That looks OK.

i plugged in this eqs i = (.0059)/(394*121084*0.8)

When used to make the giant coil there's only one turn.

 

[mba444]

thanx again i got the right answer