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20-11 The Hall Effect

20-11 The Hall Effect.

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20-11 The Hall Effect

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  1. 20-11 The Hall Effect • When a current-carrying conductor is held firmly in the magnetic field, the field exerts a sideways force on the charges moving in the conductor. This results in a potential difference in the conductor. When the potential difference builds up and produces electric field EH it produces and exerts a force eEH , that is equal and opposite to the magnetic force…this is called the Hall effect. • The potential difference produced is called the Hall emf.

  2. 20-12 Mass Spectrometer • Mass spectrometers were designed to measure the mass of atoms. Ions are produced by heating substances to high temperatures… • If the electric force qE up on + ions is just balanced by magnetic force qvB (down on positive ions) is balanced, then the ion will pass through a selector slit. ( qE=qvB or v=E/B • Isotopes were found in this way, because only ions or atoms of the same mass pass through the slit. (see p607 and p608) • See Example 20-14 p608

  3. 20-13 Ferromagnetism; Domains *Some materials can be made into ‘permanent’ magnets. These materials are said to be ferromagnetic. Small, often microscopic regions, called domains, (at most 1mm) are aligned in ferro-magnetic substances. They are random in non-ferromagnetic substances. Above a certain temperature, called the Curie Temperature, (1043 K for iron) no magnetism can be produced at all

  4. 20-14 Electromagnets and Solenoids *When a coil is wrapped around iron, or other ferromagnetic substance, an electromagnet can be produced. *Electromagnets have many uses. (see p 611)

  5. 20-15 Magnetic Fields in Magnetic Materials ; Hysteresis *The magnetic field inside a solenoid can be found using B0 = u0nI When a ferromagnetic material is inside a solenoid we use the formula: B = u nI where u is the magnetic permeability of the material in the center of the solenoid or electromagnet. *Measurements of magnetic materials are often made using a torus, which is an iron ring solenoid. * Hysteresis is a curve resulting from these measurements, using a torus, where the curves do not retrace their data points of the previous curve.

  6. Homework ch20TXTD • P618-619 prob. 47,50-51,56

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