Solenoids and Electromagnets A

Before you can use electromagnetic force, you need to be able to control it. Using electromagnetic force requires some simple tools. Figure 9A shows a current-carrying wire with a loop in it. The magnetic field in the center of the loop points right to left through the loop, as shown in Figure 9A.

Suppose you loop the wire many times to make a coil, as shown in Figure 9B. Then the magnetic fields of the loops combine so that the coiled wire acts like a bar magnet. The field through the center of the coil is the sum of the fields B from each turn of the wire. A coil of current-carrying wire that produces a magnetic field is called a solenoid.

If you place a ferromagnetic material, such as an iron rod, inside the coil of a solenoid, the strength of the magnetic field increases. The magnetic field produced by the current causes the iron rod inside the coil of the solenoid to become a magnet. An electromagnet is a solenoid with a ferromagnetic core. Changing the current in an electromagnet controls the strength and direction of its magnetic field. You can also use the current to turn the magnetic field on and off. People use many devices every day, such as hair dryers, telephones, and doorbells, that utilize electromagnets.

Figure 9 The magnetic field lines around a solenoid are like those of a bar magnet. Applying Concepts Which of the poles is north?

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