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OBJECTIVES:
At the end of this Lesson, the learners should be able to:
1. Identify Resistance, Current and Voltage
2. Define Ohm’s Law
3. Solve the equation using ohm’s law
LEARNING COMPETENCIES:
1. Determine the meaning of symbols, key terms, and other domain-specific
words and phrases as they are used in a specific scientific or technical
context
2. Evaluate the resistance, current and voltage in a circuit.
3. Infer the relationship between current, voltage and resistance.
WHAT I NEED TO KNOW
“Ohm law states that at a constant
temperature, the current (I) flowing through
the resistor is directly proportional to the
voltage or potential difference (V) applied
across the resistor”.
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Direction: Define the following
PRETEST 1
You must complete the sentence.
Be aware that some words can be
used several times.
1. A Resistor is _________________________________________________________________
2. A current is ________________________________________________________________
3. A voltage is _______________________________________________________________.
4. Ohm’s Law _______________________________________________________________
5. Electricity _________________________________________________________________.
6. Ohm ____________________________________________________________________.
7. Volt _____________________________________________________________________.
8. Ampere _________________________________________________________________.
9. Resistance _______________________________________________________________.
10. Circuit ___________________________________________________________________.
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ACTIVITY 1
Direction: Using Ohm’s Law solve the following problem. Show your solutions. (note:
Don’t forget the units)
1.
What is the current in a 160V circuit if the resistance is 2Ω?
2.
What is the current in a 160V circuit if the resistance is 20Ω?
3.
What is the current in a 160V circuit if the resistance is 10Ω?
4.
What is the current in a 160V circuit if the resistance is 5Ω?
5.
Based on questions 2, 3 and 4, what happens to the current in a circuit as the
resistance decreases?
6.
Based on questions 2, 3 and 4, what happens to the current in a circuit as the
resistance increases?
7.
What voltage is required to move 6A through 5Ω?
8.
What voltage is required to move 6A through 10Ω?
9.
What voltage is required to move 6A through 20Ω?
10.
Based on questions 6,7, and 8, what happens to the voltage required in a circuit as
the resistance decrease? increase
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Ohms law, sometimes more correctly called Ohm’s Law, named after Mr. Georg
Ohm, mathematician and physicist born 1789 and died 1854 in Bavaria, defines the
relationship between power, voltage, current and resistance. These basic electrical
units apply to direct current, or alternating current. Ohm’s Law is the foundation of
electronics and electricity. These formulae are very easy to learn and are used
extensively by electricians. Without a thorough understanding of “Ohm’s Law” an
electrician would either design or troubleshoot even the simplest of electronic or
electrical circuits. Ohm established in the late 1820’s that if a voltage was applied to
a resistance then “current would flow and then power would be consumed”.
A.C OR D.C
Voltage
H
E
A
T
Ohm’s Law power consumption through a resistance
Some practical every day examples of this basic rule are: base board heaters,
electric frying pans, toasters and electric light bulbs. The heater consumes power
producing heat for warmth, the frying pan consumes power producing heat for
general cooking, the toaster consumes power producing heat for cooking toast, and
the electric light bulb consumes power producing heat and more important light. A
further example is an electric hot water system. All are examples of Ohm’s Law at its
most basic.
Current is directly proportional to voltage. If voltage is increased by a
given percentage, current increase by the same percentage. If the voltage is
decreased by a given percentage, current decreases by the same percentage.
Current is inversely proportional to resistance. An increase in resistance
results in a decrease in current. A decrease in resistance results in an increase in
current. It is important to note that resistance cannot be changed by changing
voltage or current. Resistance in a circuit is a physical constant. Resistance in a
circuit can only be changed by changing components or resistors rated at more or
fewer ohms.
V
EXAMPLE
1.
V
An alarm clock draws 0.5A of current
when connected to 120V circuit.
Calculate the resistance.
Resistance: R = V ÷ I = 120V ÷ 0.5A = 240Ω
2.
How much current flows through a radio
that has a resistance of 4.0 Ω when 16 V is
impressed across the speaker?
I = V ÷ R = 16 V ÷ 4 Ω = 4 A
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HOW MUCH HAVE YOU LEARNED
ASSESSMENT 1
Direction: Solve the following using Ohm’s Law. (Show your solution.)
1.
A subwoofer needs a households voltage of 110V to push a current of 5A
through its coil. What is the resistance of the subwoofer?
2.
An iPod uses a standard 1.5 V Battery? How much resistance is in the circuit if
it uses a current of 0.01A?
3.
A circuit contains a 1.5 volts battery and a bulb with resistance of 3 ohms.
Calculate the current.
4.
What current flows through a hair dryer plugged into a 120 Volt circuit if it has
a resistance of 20Ω?
5.
What happens to current in a circuit if a 1.5-volt battery is remove and is
replaced by a 2-volt battery?
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6.
A 110 volt wall outlet supplies power to a strobe light with a resistance of
2200 ohms. How much current is flowing through the strobe light?
7.
A CD player with a resistance of 40 ohms has a current of 0.1 amps flowing
through it. Sketch the circuit diagram and calculate how many volts
supply the CD player?
8.
A 120-volt power source supplies a lamp with a resistance of 192 ohms.
What is the current flow of the circuit?
9.
What is the resistance of the circuit conductors when the conductor
voltage drop is 3 volts and the current flowing through the conductors is
100 amperes?
10. Given: I=15A, R=2Ω, Find E.
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