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
_
FE
_
FE
q1 q2
FE
_
q2
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 Fields
A. Act over a distance
B. 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 generator
B. Conductors—metal wire or metal
connections
C. Load—appliance or machine
D. Control elements—switches, volume
controls
E. 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—anode
b. 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