Unit 9 lenz’s law

Lenz's law might have been predicted from the principle of the conservation of energy. When you move a magnet toward a coil and thus induce a current in its windings, the induced current heats the wire. In order to supply the energy to do this, you must do work in overcoming an oppos­ing force. If the force did not oppose the motion, you would create energy. Thus the magnetic field of the induced current is seen to oppose the change.

Lenz's law and the right hand rule can be used to determine the direction of an induced current. The north pole of a magnet being moved closer to a coil, the induced current causes a field which opposes the motion, a north pole being produced on the nearer face. To cause this north pole, magnetic lines must emerge from the face of the coil. Now grasp the coil with your right hand, so that your fingers point in the direction of the induced magnetic field. Your thumb will point in the direction of the current, that is, counterclockwise.

The Induced Current Opposes the Change. A magnet pole being moved toward one face of a coil, the current induced in the coil produces a magnetic field. Moreover, this field always opposes the change of magnetic flux that is occurring. For example, move the north pole of a magnet closer to one face of a coil. The induced current will be counterclockwise and will oppose the change of flux through the coil. Remove the bar magnet, and the induced current in the coil will be clockwise, again opposing the change. This rule is expressed by Lenz's law, as follows:

Whenever a current is induced, its magnetic field opposes the change of flux.

EXERCISES I.Pick up synonyms out of the following list of words and use some of them in sentences:

to predict, movement, force, thus, for instance, reason, to eliminate, cause, strength, to supply, to foretell, motion, to provide, variation, to use, to determine, close, in this way, change, near, to define, to apply, to show, to occur, for example, to remove, to point, to take place.

2. Pick up antonyms out of the following list of words:

right, north, clockwise, upward, to insert, difficult, downward, counterclockwise, left, south, to remove, to cool, near, easy, to heat, far. DLTranslate the following sentences; observe the different meanings of the verb to do:

1. When the molecule is placed in the electric field, the electrons try to move and do so for an instant. 2. If only a few of the insulator's molecules do release one electron each, the insulator at once completely breaks down and becomes a conductor. 3. If by some means we can change the current in a coil without changing the flux rapidly, then the current may rise and fall as suddenly as it does in a purely resistive circuit. 4. The electrons, the motion of which constitutes the current, do not actually pass from one plate of the condenser to the other through the dielectric. 5. An important question for the radio engineer to consider has to do with the shape of current which flows in a circuit connected to an alternator. 6. The emission or evaporation of electrons takes place at lower temperatures than does that of atoms.

4. Translate the following sentences with an emphatic inversion,beginning with predicatives expressed by participles:

1. Linking the two local circuits is the transmission circuit which contains two wires, and the large windings of the two induction coils. 2. Moving around the nucleus, and at a considerable distance from it are the rest of the electrons required to make the atom neutral. 3. Included for comparison are the L-cathode emission densities at the same temperatures and field strength. 4. Superimposed upon the dominant thermionic emission is a small amount of emission caused by the increasing positive potential of the anode. 5. Rotating with the lenses is a pair of double ended reflecting prisms, each of which directs the light beam from the corresponding lens forward a photocell assembly located at the front of the instrument.

4. Translate Into English:

Було виявлено, що прямий полосний магніт, що рухається в котушці із дроту, створює в ній електричний струм. Це взаємне пересування магніту й котушки й створює цей струм. Якби цей відносний рух припинився, струм перестав би текти. Чим швидше рухається катушка, тим більше наведена е.р. с.

4. Formulate Lenz’s Law.

5. Prepare short information on Lenz’s biography.