General Physics 2 – 4th Quarter
Ohm’s Law – describe the relationship among electric current, potential difference, and
electric resistance.
Electric Current – A charge per unit time measured by ammeter.
“intensité de courant” – French translation
Formula:
𝐈 =
𝐪
𝐭
where:
I = electric current
q = charge (C) Coulomb
t = time (s) Seconds
Unit: C/s or A (Ampere)
Other formula:
𝐈 =
𝐕
𝐑
where:
I = electric current
V = voltage (V) Volts
R = resistance (Ω) Ohms
Ω – omega
Georg Simon Ohm
(March 16, 1789 – July 6, 1854)
André-Marie Amperé
(January 20, 1775 – June 10, 1836)
Two Types of Current Flow
1) Conventional (+ -> -) – from positive to negative terminal
2) Electron (- -> +) – negative to positive terminal
Electrical Resistance – it is the opposition of a material to the flow of electric current.
Most electrical connections used devices called resistors.
Problem 1:
A steady current of 2.0 A flows in a wire for 16.0 s. How many coulombs of charge flow
through the wire?
Solution:
q = It
q = (2.0 A) (16.0 s)
q = 32.0 C
Problem 2:
Calculate the current through the circuit in which the voltage and resistance be 20V and
4Ω respectively.
Solution:
I =
V
R
I =
20V
4Ω
I = 5A
Problem 3:
The voltage and resistance of a circuit are given as 25V and 5Ω respectively. Calculate
the current through the circuit.
Solution:
I =
V
R
I =
25V
5Ω
I = 5A
Resistor Color Code Chart
Color
Digit
0
1
2
3
4
5
6
7
8
9
Multiplier
x 100
x 101
x 102
x 103
x 104
x 105
x 106
x 107
x 108
x 109
Tolerance
± 1%
± 2%
± 0.5%
± 0.25%
± 0.1%
± 0.05%
± 5%
± 10%
For easier remembering:
BB ROY of Great Britain had a Very Good Wife
RMA (Radio Manufacturers Association) – 1920s
Color Bands –> Resistor Color Codes
Resistors – it is the component that is used to limit or regulate the flow of electric current.
Tolerance Formula:
𝐓 = (𝐑 ∗ 𝐏)/𝟏𝟎𝟎
Example:
Brown-Black-Red-Gold
Brown – 1
Black – 0
Red – x 102
Gold – ± 5%
Translation of Color Code: 10 x 102 ± 5%
1000Ω ± 5%
Resistance: 10 x 102 = 1000Ω
Tolerance:
𝐓 = (𝐑 ∗ 𝐏)/𝟏𝟎𝟎
𝐓 = (𝟏𝟎𝟎𝟎Ω ∗ 𝟓)/𝟏𝟎𝟎
𝐓 = 𝟓𝟎Ω
Another example:
Find the resistor color code of the given resistance, 3450000Ω, assuming that the
tolerance is 10%. (3 digits)
Orange – 3
Yellow – 4
Green – 5
Yellow - x 104
Silver - ± 10%
Answer: Orange-Yellow-Green-Yellow-Silver
DC and AC Circuits
Direct Current (DC) – refers to the unidirectional propagation of electric charge.
Thomas Edison – proponent
DC Circuit can be divided into two categories:
1) Series DC Circuit – A series circuit is a circuit that contains more than one
electrical component connected one after the other in a single path.
2) Parallel DC Circuit – A parallel circuit is a circuit in which two or more electrical
components are connected across each other.
Quantity
Series Resistors
Parallel Resistors
Current (I)
I = I1 = I2 = I3…
I = I1 + I2 + I3…
Voltage (V)
V = V1 + V2 + V3…
V = V1 = V2 = V3…
Equivalent Resistance RTotal = R1 + R2 + R3…
(RTotal)
1
1
1
1
=
+
+ …
𝑅𝑇 𝑅1 𝑅2 𝑅3
Formulas:
𝐈 =
𝐕
𝐑
𝐕 = 𝐈𝐑
𝐑 =
𝐕
𝐈
Example:
1000V
IT = 1.33 A
VT = 1000V
RT = 750Ω
IT =
I1 = 1.33 A
V1 = 266V
R1 = 200Ω
I2 = 1.33 A
V2 = 532V
R2 = 400Ω
1000V
750Ω
IT = 1.33 A
V1 = I1 R1
V1 = (1.33 A) (200Ω)
V1 = 266V
V1 = I1 R1
V1 = (1.33 A) (400Ω)
V1 = 532V
V1 = I1 R1
V1 = (1.33 A) (150Ω)
V1 = 199.5V
The answers are approximation only, especially in voltage.
I3 = 1.33 A
V3 = 199.5V
R3 = 150Ω
Physics – Major Instruments and Their Uses
1) Accelerometer – Measures acceleration
2) Ammeter – Measures electric current flow
3) Anemometer – Measures wind speed
4) Barometer – Measures atmospheric pressure
5) Bolometer – Detects electromagnetic radiation
6) Caliper – Measures distances and diameters precisely
7) Calorimeter – Measures heat exchange
8) Electrometer – Measures electric charge or voltage
9) Gravimeter – Measures gravitational field variations
10) Galvanometer – Detects and measures small electric currents
11) Hydrometer – Measures liquid density or specific gravity
12) Inclinometer – Measures angles of inclination
13) Magnetograph – Records changes in Earth's magnetic field
14) Manometer – Measures pressure in gases and fluids
15) Ohmmeter – Measures electrical resistance
16) Seismometer – Detects and measures seismic waves
17) Thermometer – Measures temperature
18) Viscometer – Measures fluid viscosity
19) Voltmeter – Measures electric potential difference