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In Fig. 29-83, two infinitely long wires carry equal currents i. Each follows a 90°arc on the circumference of the same circle of radius R. Show that the magnetic field Bat the center of the circle is the same as the field Ba distance R below an infinite straight wire carrying a current Ito the left.

Short Answer

Expert verified

Proved.

Step by step solution

01

Given

Figure 29-83.

02

Understanding the concept

In this case, we take the vector sum of the magnetic fields and then use the relation for magnetic field in terms of current, distance, and angle subtended to get the required result. We will use the usual convention as which will represent the direction of the field going into the page and will represent the direction of the field coming out of page

Formula:

Magnetic field due to the circular arc at the center of arc with current (i).

B=μ0i2πRϕ

direction of B is determined by right hand thumb rule

03

 Step 3: Show that the magnetic field B→  at the center of the circle is the same as the field B→ a distance R below an infinite straight wire carrying a current I to the left

Let’s find the magnetic field due to the first and second wire separately. Adding them, we will get the net field due to both wires at the center of the arc using equation 29-9

B1=μ0i4πR+μ0i2πR·π2+μ0i4πR

This field is pointing out of the page.

For wire 2

B2=0+μ0i2πR·π2+0

This field is pointing into the page.

So the net field at the center is

Bc=B1+B2=μ0i4πR+μ0i2πR·π2+μ0i4πR-μ0i2πR·π2Bc=μ0i2πR

We can see that this expression is exactly the same as the equation for the field by a single infinite straight wire (equation 29-4).

Hence, it is proved.

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Most popular questions from this chapter

Each of the eight conductors in Figure carries 2.0Aof current into or out of the page. Two paths are indicated for the line integral. B.ds(a) What is the value of the integral for path 1 and (b) What is the value of the integral for path 2?

Figure 29-87 shows a cross section of a hollow cylindrical conductor of radii aand b, carrying a uniformly distributed currenti. (a) Show that the magnetic field magnitude B(r) for the radial distancer in the rangeb<r<ais given byB=μ0i2πra2-b2·(r2-b2)r

(b) Show that when r = a, this equation gives the magnetic field magnitude Bat the surface of a long straight wire carrying current i; when r = b, it gives zero magnetic field; and when b = 0, it gives the magnetic field inside a solid conductor of radius acarrying current i. (c) Assume that a = 2.0 cm, b = 1,8 cm, and i = 100 A, and then plot B(r) for the range 0<r<6.0cm .

A long solenoid has 100 turns/cmand carries current iAn electron moves within the solenoid in a circle of radius 2.30cmperpendicular to the solenoid axis. The speed of the electron is 0.0460c(c= speed of light). Find the currentiin the solenoid.

Figure 29-34 shows three arrangements of three long straight wires carrying equal currents directly into or out of the page. (a) Rank the arrangements according to the magnitude of the net force on wire Adue to the currents in the other wires, greatest first. (b) In arrangement 3, is the angle between the net force on wire A and the dashed line equal to, less than, or more than 45°?

Shows four identical currents iand five Amperian paths (athrough e) encircling them. Rank the paths according to the value of B.dstaken in the directions shown, most positive first.

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