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Pole). Earth's magnetic field results from the motion of its molten iron and 104. A student is given two pieces of iron and told to determine if one or both of the pieces are 107. Which diagram best represents the lines of nickel core. magnets. First, the student touches an end of one piece to one end of the other. The two magnetic flux between the ends of two bar Magnetic Fields The region where magnetic force exists around a magnet or magnets? any moving charged object is called its magnetic field. Just as a pieces of iron attract. Next, the student reverses gravitational or electric field allows objects to interact without coming into one of the pieces and again touches the ends together. The two pieces attract again. What direct contact with each other, a magnetic field allows magnets to interact does the student definitely know about the (1) SNSN without touching. A magnetic field exerts a force on any moving charge initial magnetic properties of the two pieces of and can be measured and detected by this effect. iron? [1] N N Magnetic Flux Lines Imaginary lines that map out the magnetic field around 105. Which diagram correctly shows a magnetic a magnet are known as magnetic field lines or magnetic flux lines. Iron field configuration? S N filings sprinkled on a card and held above a magnet are often used to map 108. The diagram below represents the magnetic S a magnetic field. The filings show the effects of magnetic force in the region lines of force around a bar magnet. surrounding a magnet and produce a pattern similar to the magnetic field (C) lines. Magnetic flux lines always form closed loops and never intersect. Concentrated lines of flux emerge from the N-pole of a magnet, curve N around the magnet, and then enter the S-pole of the magnet. The direction of a magnetic field is defined as the direction in which the N-pole of a (D compass would point in the field. When the field lines are curved, the direction of the field is determined by the direction of the N-pole of a compass placed along the tangent to the field at that point. Figure 4-12 shows the locations of the lines of magnetic flux around some bar magnets 106. The diagram below shows two compasses and around a horseshoe magnet. located near the ends of a bar magnet. The At which point is the magnitude of the magnetic field strength of the bar magnet greatest? Magnetic Field Strength The number of magnetic lines of flux per unit area north pole of compass X points toward end passing through a plane perpendicular to the direction of the lines is called A of the magnet. 109. The diagram below represents magnetic lines of force within a region of space. (E) the magnetic field strength, B, or flux density. Magnetic field strength is a vector quantity, as are gravitational field strength and electric field Lines of Force Figure 4-12. Magnetic field strength. lines around some bar magnets and a horseshoe magnet Bar magnet Review Questions On the diagram draw the correct orientation of the needle of compass Y and label its polarity. At which point is the magnetic field strongest? 100. In order to produce a magnetic field, an electric 103. The diagram below shows a compass placed charge must be near the north pole, N, of a bar magnet. Electromagnetic Induction Motion of (1) stationary (3) positive Electromagnetic induction is the process of generating a potential onductor (2) moving (4) negative S N difference in a conductor due to relative motion between the conductor 101. The presence of a uniform magnetic field may and a magnetic field. If the conductor "cuts" across the magnetic flux be detected by using a lines, a magnetic force acts on the electrons in the conductor, causing (1) stationary charge (3) beam of neutrons Which diagram best represents the position of the needle of a compass as it responds to the them to move from one end toward the other. This results in a difference (2) small mass (4) magnetic compass magnetic field of the bar magnet? in the amount of negative charge at each end of the conductor, in other North South 102. Which term does not identify a vector words, a potential difference. The difference in potential created in a quantity? conductor due to its relative motion in a magnetic field is called an Magnetic (1) electric charge induced potential difference. Figure 4-13 shows a potential difference field (2) magnetic field strength being induced in a conductor. Figure 4-13. Electromagnetic (3) velocity If the conductor is part of a complete circuit, an electric current is induction: The diagram shows the (4) acceleration induced. If the conductor is moved parallel to the lines of flux (that is, it direction of motion of a straight 191 (4) conductor relative to a magnetic field does not "cut" them) no potential difference is induced and there is no that produces a maximum induced current, even if the conductor is part of a complete circuit. potential difference in the conductor 34 Topic 4: Electricity and Magnetism Topic 4: Electricity and Magnetism 135