Voltage in Electrical Systems

I. Universal Forces A. Gravity 1. Newton’s universal law of gravitation 2. Fg = G (m1m2/d2) 3. G = 6.67 X 10-11 (universal gravitational constant) 4. Example 1.11, p. 49

N· m2

kg2

B. Electrical Force 1. Charge causes force

a. positive b. negative

2. Principle of conservation of charge (p. 50) 3. Coulomb’s law (p. 51) 4. FE = K (q1q2/d2) 5. Charge is in Coulombs (C)

_q1

FE _

q2FE

_

q2

FE+

q1

FE

6. K = 9.0 X 109 N∙m2/C2

7. Protons and Electrons have a charge of 1.6 x 10-19 C

8. Example 1.12, p. 52

II. Gravitational and Electric FieldsA. Act over a distanceB. Field—imaginary construction to help understand and predict how forces are transmitted. (g = Fg/m)

C. Field is a vector 1. direction of g (gravitational field) is the

direction of the force on the test mass 2. g does not depend on the size of the test mass

D. E = FE/q 1. direction of E is the direction of the force on the positive test charge 2. E does not depend on the size of the test

charge.E. Field lines:

-

III. Electric Potential A. Electric potential difference—whether a

charge will accelerate when released— electric potential or voltage

B. Unit of potential difference-Volt C. ΔVAB = E x d D. Flow of charge—current E. pump = battery

IV. Components of Electrical Systems (for a complete circuit)A. Source—battery or generatorB. Conductors—metal wire or metal

connectionsC. Load—appliance or machineD. Control elements—switches, volume controlsE. P. 56

V. Kinds of Current A. Direct Current (DC)

1. cell—primary, secondary 2. battery 3. connecting cells in series will add

voltage 4. electrodes

a. positive—anodeb. negative—cathode

5. schematic diagram (see p. 60)

B. Alternating Current (AC) 1. voltage source reverses terminals many times per second 2. frequency ( f)—cycling rate 3. frequency is measured in cycles per second—hertz