Chapter 11 Current

Introduction This chapter covers the following topics: Electrical charge Current Flow Scientific notation

Electrical Charge Like charges –Two electrons or two protons together First law of electrostatic charges –Like charges repel one another Second law of electrostatic charges –Unlike charges attract each other

Figure 11-1 Basic laws of electrostatic charges. © 2014 Cengage Learning.

Electrical Charge Negative electrons drawn toward positive protons in the nucleus –Attractive force balanced by centrifugal force caused by electron’s rotation about the nucleus Amount of attractive or repelling force: –Depends on amount of charge and distance between the bodies

Electrical Charge cont’d Coulomb (C) –Unit of electrical charge –1C = 6.24 x electrons Electrical charges created by electron displacement

Electrical Charge (cont’d.) Potential difference exists between two points with unlike charges –When points connected by a conductor, current flows

Current Flow Coulomb (C) Electrons move from an area of negative charge to an area of positive charge Ampere –Unit of measurement for current flow

Current Flow (cont’d.)

Current Flow cont’d Electric current is the flow of negative charges –Electrons flow in the same direction as current Electrons moving from one atom to the next: –Creates the appearance of a positive charge Called a hole

Figure 11-2 As electrons move from one atom to another, they create the appearance of a positive charge, called a hole. © 2014 Cengage Learning.

Figure 11-3 Electron movement occurs in the direction opposite hole movement. © 2014 Cengage Learning.

Figure 11-4 Electrons in a conductor react like Ping-Pong balls in a hollow tube. © 2014 Cengage Learning.

Figure 11-5 A voltage source can be considered a pump that supplies electrons to the load and recycles the excess electrons. © 2014 Cengage Learning.

Scientific Notation Electric current is the flow of negative charges Uses single digits and powers of ten: –To express large or small numbers Exponent indicates number of places to the right or left of the decimal point –Positive exponent moves decimal to the right –Negative exponent moves decimal to the left Example: 3 x 10 3 = 3.0 x 10 3 = 3000

Scientific Notation (cont’d.) Example: 3 x = 3.0 x = Milliampere (mA) and microampere ( μA) are more frequently found in low-power electronic circuits than amperes

Figure 11-6 Prefixes commonly used in electronics. © 2014 Cengage Learning.

Scientific Notation (cont’d.)