. Practical physics. g a zinc salt, how much zinc would be deposited in the same time? 4. How could a silver oup be given a gold lining by use of theelectric current? 5. If the terminals of a battery are immersed in a glass of acidulatedwater, how can you tell from the rate of evolution of the gases at thetwo electrodes which is positive and which is negative ? 6. The coulomb (§ 305) is 3 billion times as large as the electrostaticunit of quantity defined in § 280. How many electrons pass per secondby a given point on a lamp filament which is carrying 1 ampere ofcurrent (see § 284) ? \ 252 ELE
. Practical physics. g a zinc salt, how much zinc would be deposited in the same time? 4. How could a silver oup be given a gold lining by use of theelectric current? 5. If the terminals of a battery are immersed in a glass of acidulatedwater, how can you tell from the rate of evolution of the gases at thetwo electrodes which is positive and which is negative ? 6. The coulomb (§ 305) is 3 billion times as large as the electrostaticunit of quantity defined in § 280. How many electrons pass per secondby a given point on a lamp filament which is carrying 1 ampere ofcurrent (see § 284) ? \ 252 ELECTRICITY IN MOTION Magnetic Effects of the Current ; PropertiesI of Coils 306. Shape of the magnetic field about a current. If we place the wire which connects the plates of a galvanic cell in a vertical i^osi-tion (Fig. 249) and explore with a compass needle the shape of themagnetic field about the current, we find that the magnetic lines areconcentric circles lying in a plane perpendicular to the wire and having. Fig. 249 Fig. Magnetic field about a current the wire as their common center. We find, moreover, that reversing thecurrent reverses the direction of the needle. If the current is very stiong(say 40 amperes), this shape of the field can be shown by scattering ironfilings on a plate through which the current passes (Fig. 249). If the cur-rent is weak, the experiment should be performed as indicated in Fig. 250. The relation between thedirection in which the currentflows and the direction in whichthe jV pole of the needle points(this is, by definition, the direc-tion of the magnetic field) is given in the following conven-ient rule, known as Amperes Rule: If the right hand graspsthe wire as in Fig. 251^ so that tlbe- thumb points in the directionin whioh t?i£ current is flowing, then the magnetic lines encirclethe tvvre in tJie same direction as do the fingers of the hand.
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectphysics, bookyear1922
