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Text 3. Electromagnetic forces and fields
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- PRE-READING
- Active vocabulary Word Pronunciation Translation
- Magnetic fields and lines of force
| Text 3. Electromagnetic forces and fields
«Is it a fact — or have I dreamt it — that, by means of electricity, the world of matter has become a great nerve, vibrating thousands of miles in a breathless point of time?» Nathaniel Hawthorne PRE-READING In a small group discuss these problems and make notes of your main points. Then share opinions. 1) Any wall plug is a dipole driven by an alternating electric field. Why does not a wall plug, delivering 230 V or 100 V at 50 Hz or 60 Hz, radiate electromagnetic fields? 2) Why does a voltage transformer contain a ferromagnetic core? 3) Are there electromagnetic motors in biological systems? Active vocabulary Word Pronunciation Translation acceleration, n. /əkˌseləˈreɪʃən/ ускорение ammeter, n. /ˈæmiːtər/ амперметр axis, n. /ˈæksɪs/ ось current, n. /ˈkʌrənt/ ток centripetal force /ˌsentrɪˈpiːtəl fɔːs / центростремительная сила device, n. /dɪˈvaɪs/ устройство, приспособление, syn. gadget galvanometer, n. /ˌɡælvəˈnɑmɪt ər/ гальванометр generator, n. /ˈdʒenəreɪtər/ генератор grasp, v. /ɡrɑːsp/ схватывать, сжимать, syn. grab, clutch, seize magnetite, n. /ˈmæɡnɪta i t/ магнетит, магнитный железняк motor, n. /ˈməʊtər/ двигатель, мотор plane, n. /pleɪn/ плоскость radius, n. /ˈreɪdiəs/ радиус resistor, n. /rɪˈzɪstər/ резистор, катушка сопротивления sensitive, adj. /ˈsensɪtɪv/ чувствительный 68 solenoid, n. /ˈsəʊlənɔɪd/ соленоид spectrometer, n. /spekˈtrɒmɪtər/ спектрометр thumb, n. /θʌm/ большой палец toroid, n. /tərɔɪd/ тороид torque /tɔːrk/ вращающий момент voltmeter, n. /ˈvəʊltˌmiːtər/ вольтметр READING Read and translate the text using a dictionary if necessary: The magnetic field of naturally occurring magnetite is too weak to be used in devices such as modern motors and generators; these magnetic fields must come from electric currents. Magnetic fields affect moving charges, and moving charges produce magnetic fields; therefore, the concepts of magnetism and electricity are closely linked to each other. Magnetic fields and lines of force A bar magnet attracts iron objects to its ends, called poles. One end is the north pole, and the other is the south pole. If the bar is suspended so that it is free to move, the magnet will align itself so that its north pole points to the geographic north of the earth. The suspended bar magnet acts like a compass in the earth's magnetic field. If two bar magnets are brought close together, the like poles will repel each other, and the unlike poles attract each other. This magnetic attraction or repulsion can be explained as the effect of one magnet on the other, or it can be said that one magnet sets up a magnetic field in the region around it that affects the other magnet. The magnetic field at any point is a vector. The direction of the magnetic field (B) at a specified point is the direction that the north end of a compass needle points at that position. Magnetic field lines, analogous to electric field lines, describe the force on magnetic particles placed within the field. Iron filings will align to indicate the patterns of magnetic field lines. жүктеу/скачать 1,14 Mb. Достарыңызбен бөлісу:
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