Electrolysis of copper sulphate solution using copper electrodes When copper electrodes are used the action at the cathode is exactly the same as with platinum or carbon electrodes. Cu2+ ions are discharged and deposited on the cathode. At the anode, however, copper ions go into solution in preference to the discharge of either OH – or S042 – […]
Magnetic flux due to current in two vertical parallel wires If two parallel wires are arranged side by side vertically and carry currents in the same direction the magnetic flux in a horizontal plane close to the wires is as shown in Fig. 36.16. A neutral point is formed between the wires, its exact position depending on the […]
Resultant magnetic flux in a horizontal plane due to the earth and the current in a long vertical wire The iron-filings method described on page 420 to investigate the magnetic flux due to a current in a long straight wire gives information only about the strong field very close to the wire. In order to study the field […]
The telephone receiver (earpiece) The telephone receiver contains a U-shaped magnet formed by placing a short permanent bar magnet across the ends of two soft-iron bars (Fig. 36.14). This is placed so that it exerts a pull on a springy magnetic alloy diaphragm. Two solenoids are wound in opposite directions on the soft-iron bars. When a person speaks […]
Magnetic separators An electromagnetic separator, used for the purpose of removing tramp iron from crushed copper ore, is shown in Fig. 36.13. A miscellaneous collection of iron objects, including nuts and bolts, etc., finds its way into the ore, and must be removed before smelting. This is done by passing the ore on a conveyor belt past […]
The solenoid switch (magnetic relay) The current required by the starter motor of a car is very high, and this requires very thick cable and a switch with heavy contacts. For convenience, a solenoid switch is used, the operation of which will be understood from Fig. 36.12. The starter switch, taking only a small current, is usually incorporated in […]
The electric bell The electric bell consists of two solenoids wound in opposite directions on two softiron cores joined by a soft-iron yoke (Fig. 36.11). One end of the windings is connected to a terminal T1, and the other to a metal bracket which supports a spring mounted soft-iron armature. The armature carries a light spring, to […]
lifting magnets Fig. 36.9 illustrates a powerful double electromagnet used in industry for lifting and transporting steel plates, girders, scrap iron, and so on. When the load has been carried to the desired position it is released by switching ofT the current. Fig. 36.10 shows a lifting magnet in section. It is made of magnetically soft iron, with […]
The electromagnet The solenoid method for magnetizing steel described on page 343 was first used for making magnetic needles by Ampere in 1820. Five years later a Lancashire man named William Sturgeon used soft iron instead of steel and found that the iron was strongly magnetized only when the current was flowing. Sturgeon’s electromagnet was made of a […]
Magnetic flux due to a short circular coil When a current is passed through a short circular coil the pattern of the magnetic flux is shown in Fig. 36.6 (b). The coil used for this experiment consists of twenty or more turns closely wound together and fixed to a thin hardboard table (Fig. 36.6 (a)). Current is […]