Истории и востоковедения
Magnetic field of a long, straight wire
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- Бұл бет үшін навигация:
- Amperes law
- Magnetic fields of the loop, solenoid, and toroid
| Magnetic field of a long, straight wire
A current ‐carrying wire generates a magnetic field of magnitude B in circles around the wire. The equation for the magnetic field at a distance r from the wire is , where I is the current in the wire and μ (the Greek letter mu) is the proportionality constant. The constant, called the permeability constant, has the value . The direction of the field is given by a second right ‐hand rule, shown in Figure 4. Using the second right-hand rule you can determine the direction of the magnetic field resulting from a current. Grasp the wire so that your thumb points in the direction of the current. Your fingers will curl around the wire in the direction of the magnetic field. Ampere's law Ampere's law allows the calculation of magnetic fields. Consider the circular path around the current. The path is divided into small elements of length (Δ l). Note the component of B that is parallel to l and take the product of the two to be B ∥ l. Ampere's law states that the sum of these products over the closed path equals the product of the current and μ , . Magnetic fields of the loop, solenoid, and toroid A current generates a magnetic field, and the field differs as the current is shaped into (a) a loop, (b) a solenoid (a long coil of wire), or (c) a toroid (a donut ‐shaped coil of wire). The equations for the magnitudes of these fields follow. The direction of the field in each case can be found by the second right ‐hand rule. Figure 5 illustrates the fields for these three different configurations. 71 Figure 5 Magnetic field resulting from (a) a current loop, (b) a solenoid, and (c) a toroid. a) The field at the center of a single loop is given by , where r is the radius of the loop. b) The field due to a solenoid is given by B = μ 0 NI, where N is the number of turns per unit length. c) The field due to a toroid is given by , where R is the radius to the center of the toroid. (Adopted from www.cliffsnotes.com ) жүктеу/скачать 1,14 Mb. Достарыңызбен бөлісу:
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