how to get the charge q = -1.60 x 20^-19 22 CHAPTER 25 Current, Resistance, and
ID: 2085886 • Letter: H
Question
how to get the charge q = -1.60 x 20^-19 22 CHAPTER 25 Current, Resistance, and Electromotive Force closed loop, called a complete circuit. In such a steady situation, the total charge in every segment of the conductor is constant. Hence the rate of flow of charge out at one end of a segment at any instant equals the rate of flow of charge in at the other end of the segment, and the current is the same at all cross sections of the circuit. We'll make use of this observation when we analyze electric circuits later in this chapter In many simple circuits, such as flashlights or cordless electric drills, the direction of the current is always the same; this is called direct current. But home appliances such as toasters, refrigerators, and televisions use alternating current, in which the current continuously changes direction. In this chapter we'll con sider direct current only. Alternating current has many special features worthy of detailed study, which we'll examine in Chapter 31 Example 25.1 Current density and drift velocity in a wire The magnitude of the current density is then An 18-gauge copper wire (the size usually used for lamp cords). with a diameter of 1.02 mm, carries a constant current of 167 A to a 200-W lamp. The free-electron density in the wire is 8.5 × 1028 per cubic meter. Find (a) the current density and (b) the drift speed 1.67 A 8.17 x 10' A (b) From Eq (25.3) for the drift velocity magnitude we find 2.04 × 106 A/m 2 (8.5 × 1028 tn.Y-1.60 × 10.19 1.5 × 10-4 m/s 0.15 mm/s IDENTIFY and SET UP: This problem uses the relationships among current I, current density J, and drift speed g. We are given I and the wire diameter d, so we use Eq. (25.3) to find J. We use Eq (25.3) again to find g from J and the known EXECUTE: (a) The cross-sectional area is EVALUATE: At this speed an electron would require 6700 s (almost 2 h) to travel I m along this wire. The speeds of random motion of the electrons are roughly 10m/s, around 100 times the drift speed. Picture the electrons as bouncing around frantically, with a very slow drift n/2 (102 × 10 , m)--8.17 × 10-7 m/
Explanation / Answer
#Your question is that in the example above, how you got charge 1.6 ×10^-19
So, the |Q| charge ( 1.6 × 10^-19 ) is the charge of an electron.
This is the universal value of electron charge.
Anywhere in any condition the charge of an electron will be -1.6 × 10^-19. And it's magnitude will be 1.6 × 10^-19.
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