School: St. Andrew Technical High
School
Subject: Electrical Technology
Name of Student Teacher:
Jermaine Kelly
Grade 8C
What is Electromotive Force?
• Energy per unit charge that is imparted by an
energy source, such as an electric generator
or a battery.
What am I ?
Topic for today’s lesson:
Fundamentals of Ohms law.
Outcome:
• state the name of the scientist that observe
the relationship of ohms law to 100% accuracy
without using the note book.
• state the definition of ohms law to 100 %
accuracy without assistance from others.
• Define electric current of to 100 % accuracy
without assistance from others.
Outcome:
•describe voltage correctly without assistance
from the class.
•what resistance is to precision based on the
explanation that is presented in class.
•perform calculations using ohms law formula
accurately without assistance from others
The beginning of Ohms law.
• Ohms law was revealed by Georg Ohm
who was born March 16, 1789, in
Germany, he died in July 6, 1854; Mr.
Ohm is a German physicist who also
bears the name of the unit of resistance.
He observed the relationship among
current (I), voltage (V) and resistance (R
).
Definition of ohms law.
Ohms law indicated that the electrical
current in a circuit is directly proportional
to the applied voltage and is inversely
proportional to the resistance in a circuit
at a constant temperature.
Graph explain ohms law
3. Definition of electric current.
An electric current is a flow of electric charge.
In electric circuits this charge is often carried by
moving electrons in a wire. It can also be
carried by ions in an electrolyte. The unit of
electric current is amps or amperes and is
represented by the letter A.
Definition of voltage
Voltage is the pressure from an electrical
circuit’s power source that pushes
charged electrons (current) through a
conducting loop, enabling them to do
work such as illuminating a light
Voltage is represented by the letter Vor E
Definition of resistance.
• Resistance is an electrical quantity that
measures how the device or material
reduces the electric current flow
through it.
• The resistance is measured in units of
ohms (Ω). The symbol to represent
resistance is R.
The Formula for ohms law
•
V=IR
•
I=V/R
•
R = V/I
Where:
V - is the voltage that is measured in volts (V)
I – is the current that is measured in Ampears (A).
R – is the resistance that is measured in ohms (Ω).
Ohms law calculations
•Suppose that a circuit has 1,000 Ω of
resistance with 150 V of applied voltage. What
is the current ?
Solution
•I = V / R
•I = 150 / 1000 Ω
• = 0.15A
Definition of electric power.
•Electrical power is the rate at which electrical
energy is used. The unit of electrical power is
watt which is named after the scientist James
Watt, and is represented by the symbol W.
•There are three basic formulas to find the
Electric power in a circuit.
•
P = IV
•
P = I2 R
•
P = V2/R
Calculations
• If a circuit has 50 milli -amperes of
current flow and an applied voltage of
10V, how much power does the circuit
dissipate? Using the basic formula for
power:
solution
• P = IV
• P = 10V ×50mA
Calculations
• If a circuit has a voltage of 75 V and a
resistance of 15 Ω , how much power
does the circuit dissipate? Using the
basic formula for power:
Class Activity
•
Instructions: Answer the following questions on a separate sheet of paper.
Show all work and formulas.
V = I×R
•
1.
What is the voltage in a circuit that has a current
of 2.4 A and a resistance of 4 Ω ?
• 2.
A circuit has a resistance of 12 and draws a current of
6 A what is the potential difference in the circuit?
• 3.
A TV set uses a current of 12 A and has a
resistance of 10 Ω, what is the potential difference?
• 4.
A toaster has a resistance of 60 Ωand is plugged into a 120 V
power supply, what is the current in the toaster?
Summary
• What is the formula of Ohms law ?
• What is name of the scientist that discovered
ohms law?
• What is the formula to calculate power ?
• What is the unit of resistance?