UNIT 5
UNIT 5
ELECTRICITY
ELECTRON’S CHARGE, e-
(Units of Coulombs (C))
e- = 1.6 x 10 -19 C
A lightning strike has
about 20 -30
Coulombs of charge!
STATIC ELECTRICITY
Opposites Attract!
INSULATORS VS. CONDUCTORSInsulators (non-conductors) Conductors
Charges are stuck where you put them Charges are able to move freely &
spread out
Ex: wood, rubber, glass Ex: metals, water, human body
*Semi-conductors are
somewhere in between*
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UNIT 5
ELECTRIC FORCE
COULOMB’S LAW
ELECTROSTATIC FORCE
(Units of Newtons (N))
Distance between
particles (in m)
Charge of 2nd particle
(in Coulombs)
𝐹𝑒 = k(𝑞1 ∗ 𝑞2)
𝑑2
Charge of 1st particle
(in Coulombs)
Coulomb’s constant
k = 9 x 109 N·m2/ C2
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UNIT 5
ELECTRIC FIELDS
ELECTRIC FIELD
POSITIVELY CHARGED OBJECT
So we draw field lines radiating outward from
a positively charged object.
+
ELECTRIC FIELD
NEGATIVELY CHARGED OBJECT
So we draw field lines radiating toward a
negatively charged object.
-
UNIT 5
CIRCUITS
CURRENT
I = Current (amps, A)
V = Voltage (volts, V)
R = Resistance (ohms, Ω)
POWER
P = Power (watts, W)
V = Voltage (volts, V)
I = Current (amps, A)
EXAMPLEA light bulb in a circuit with a 12 V battery uses 24 watts.
What is the resistance of the light bulb?
EXAMPLEA light bulb in a circuit with a 12 V battery uses 24 watts.
What is the resistance of the light bulb?
G: V = 12 V
P = 24 W
U: R = ? I =?
E: I = V/R R = V/I
P = VI I = P/V
S: I = 24W / 12 V = 2 amps
R = 12 V / 2 A = 6 ohms
R = 6 ohms
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What is the total resistance of this
circuit?
12 V
1 Ω2 Ω
3 Ω
UNIT 5
SERIES
-CURRENT CONSTANT
V I R
R1 2 V 2 A 1 Ω
R2 4 V 2 A 2 Ω
R3 6 V 2 A 3 Ω
Total 12 V 2 A 6 Ω
UNIT 5
PARALLEL
-VOLTAGE CONSTANT
PARALLEL CIRCUITS
What is the total
resistance?
V I R
R1 9 V 3 A 3 Ω
R2 9 V 1.8 A 5 Ω
R3 9 V 1.5 A 6 Ω
Total 9 V 6.30 A 1.428 Ω
UNIT 5
COMBINATION
Total resistance =
Total current =
COMBINED CIRCUIT EXAMPLE
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UNIT 4
MAGNETISM
•Close together = STRONG field
•Far apart = WEAK field
•Fields are strongest at the poles
Magnetic Fields: surrounds a magnet and exerts
a magnetic force on other objects
Start
NorthEnd
South
MAGNETIC FIELDS
Earth behaves like a
large bar magnet
•North magnetic pole of
the earth is at the
physical south pole
•South magnetic pole
of the earth is at the
physical north pole
How Does a Compass Work?
To find direction of magnetic field due to a current carrying
wire, point the thumb of your right hand along the wire in
the direction of the current I.
Your fingers are now curling around the wire in the direction
of the magnetic field.
RIGHT HAND STRAIGHT WIRE RULE
When the fingers of the right-hand curl around
a solenoid in the direction of the current, the
thumb points to the NORTH POLE
RIGHT HAND SOLENOID RULE
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