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MRI (magnetic resonance imaging) is a medical technique that produces detailed 鈥減ictures鈥 of the interior of the body. The patient is placed into a solenoid that is 40 cm in diameter and 1.0 m long. A 100 A current creates a 5.0 T magnetic field inside the solenoid. To carry such a large current, the solenoid wires are cooled with liquid helium until they become superconducting (no electric resistance).

a. How much magnetic energy is stored in the solenoid? Assume that the magnetic field is uniform within the solenoid and quickly drops to zero outside the solenoid.

b. How many turns of wire does the solenoid have?

Short Answer

Expert verified

Energy stored in solenoid is1.25106J, and solenoid have 4104turns.

Step by step solution

01

Part (a). Given information 

We have given that, the solenoid has 40 cm diameter and 1.0 m length. A 100 A current creates a 5.0 T magnetic field inside the solenoid.

02

.

To calculate the total energy of solenoid, we have to determine volume and energy density.

The formula to calculate volume is :

Vsol=r2soll

Here, Vsol= volume of solenoid

rsol= radius of solenoid

l= length of solenoid

Substituting the values in the formula :

localid="1651030697382" V=(0.20m)2(1.0m)

V=0.126m3

Now we will calculate the the value of energy density of solenoid.

The formula of energy density is :

B=120B2

Here, B= Energy density

0=Permeability constant

B= Magnetic field

Substituting the values in the formula :

localid="1651030882723" B=(5.0T)22(410-7H/m)

localid="1651031066068" B=9.95106J/m3

03

Step 2.

Now we will calculate the value of stored energy.

The formula for the stored energy is :

Utot=BVsol

localid="1651031003274" Utot=(9.95106J/m-3)(0.120m3)

Utot=1.25106J

The stored energy of solenoid is1.25106J.

04

Part (b). Given information 

We have given that, the solenoid has 40 cm diameter and 1.0 m length. A 100 A current creates a 5.0 T magnetic field inside the solenoid.

05

Step 1. 

The formula for the number of turns of wire is :

N=Blsol0I

Here, N= Number of turns of wire

lsol= Length of solenoid

0= Permeability constant

I= Current

06

Step 2. 

Substituting the values in the formula :

N=(1.0m)(5.0T)(410-7H/m)(100A)

N=4.0104

Total number of turns is4.0104.

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