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1.1.1. If I were an electrician I should know how to reduce the resistance of the conductor.
1.1.2. A torque would have been applied to the body if we had produced angular acceleration.
1.1.3. If the students had received and read books on their speciality they would not have broken the device.
1.1.4. The volume of gas will be proportional to its absolute temperature provided its pressure remains constant.
1.1.5. If you study the Physics of semiconductors, you will know the properties of the p-n junction better.
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1.2.1. If the sand (to be) not refractory enough, it will fuse with the metal.
1.2.2. I should come and see you off if I (not to live) so far away.
1.2.3. He (to call) her up yesterday if he had been in town.
1.2.4. We (to deliver) the lathes in December provided we receive your order within the next ten days.
1.2.5. Your health (to improve) unless you took better care of yourself.
, 䳺 (The Absolute Participle Complex).
1.3.1. A hold-back gear being installed, the run back of the belt became impossible.
1.3.2. A fault between wires occurring, the rectifier is short-circuited and the current flows through the relay and its associated circuit.
1.3.3. The temperature of the melting ice rising, the movement of its molecules is speeded up.
1.3.4. Automation appeared at the time when the proper state of science was achieved, its roots spanning many centuries and many lands.
1.3.5. The workpiece having been sandblasted, all scale was removed.
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1.5.1. We believe the molecule of pyridine to be just like one of benzene.
1.5.2. You know the pressure to decrease as altitude increases.
1.5.3. A tooth clutch allows the rope to be adjusted for various lengths of haul.
1.5.4. We heard the construction of railway facilities benefit fully from their ability.
1.5.5. They saw concrete piers be prefabricated on shore in large hollow sections.
, ᒺ (Complex Subject). .
1.6.1. The cell is said to be polarized when a small torch bulb is joined to the terminals.
1.6.2. The water seems to be boiling.
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1.6.3. He is announced to have been appointed director of the big enterprise.
1.6.4. Coal was found to be rather abrasive.
1.6.5. The weather appeared to be improving.
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Induction motors
An induction motor or asynchronous motor is a type of alternating current motor where power is supplied to the rotor by means of electromagnetic induction.
An electric motor converts electrical power to mechanical power in its rotor (rotating part). There are several ways to supply power to the rotor. In a DC motor this power is supplied to the armature directly from a DC source, while in an induction motor this power is induced in the rotating device. An induction motor is sometimes called a rotating transformer because the stator (stationary part) is essentially the primary side of the transformer and the rotor (rotating part) is the secondary side. Unlike the normal transformer which changes the current by using time varying flux, induction motors use rotating magnetic fields to transform the voltage. The primary side's current creates an electromagnetic field which interacts with the secondary side's electromagnetic field to produce a resultant torque, thereby transforming the electrical energy into mechanical energy.
Induction motors are now the preferred choice for industrial motors due to their rugged construction, absence of brushes (which are required in most DC motors) andthanks to modern power electronicsthe ability to control the speed of the motor. The basic difference between an induction motor and a synchronous AC motor is that in the latter a current is supplied into the rotor (usually DC) which in turn creates a (circular uniform) magnetic field around the rotor. The rotating magnetic field of the stator will impose an electromagnetic torque on the still magnetic field of the rotor causing it to move (about a shaft) and rotation of the rotor is produced. It is called synchronous because at steady state the speed of the rotor is the same as the speed of the rotating magnetic field in the stator.
By way of contrast, the induction motor does not have any direct supply onto the rotor; instead, a secondary current is induced in the rotor. This changing magnetic field pattern induces current in the rotor conductors. These currents interact with the rotating magnetic field created by the stator and in effect causes a rotational motion on the rotor. However, for these currents to be induced, the speed of the physical rotor must be less than the speed of the rotating magnetic field in the stator, or else the magnetic field will not be moving relative to the rotor conductors and no currents will be induced. If by some chance this happens, the rotor typically slows slightly until a current is re-induced and then the rotor continues as before.
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1. How does the motor transform mechanical power into electrical one?
2. Which parts of the motor are movable and stationary?
3. Why are induction motors now the preferred choice for industrial motors?
4. What is difference between an induction motor and a synchronous AC motor?
5. What should we do for these currents to be induced?
