Science IICompetency No. 14 Apply Ohm's Law to series and parallel circuits.

TITLE: INTERVENTION MATERIAL ON APLICATION OF OHM'S LAW TO SERIES AND PARALLEL CIRCUITS

INTRODUCTION

How can you practically apply the ohm's law in your daily life?

OBJECTIVE: To apply the ohm's law in making the series and parallel circuits

DISCUSSION: SOURCE VOLTAGE is not affected by either current or resistance. It is either too low, normal, or too high. If it is too low, current will be low. If it is normal, current will be high if resistance is low, or current will be low if resistance is high. If voltage is too high, current will be high. CURRENT is affected by either voltage or resistance. If the voltage is high or the resistance is low, current will be high. If the voltage is low or the resistance is high, current will be low. RESISTANCE is not affected by either voltage or current. It is either too low, okay, or too high. If resistance is too low, current will be high at any voltage. If resistance is too high, current will be low if voltage is okay. NOTE: When the voltage stays the same, such as in an Automotive Circuit... current goes up as resistance goes down, and current goes down as resistance goes up. Bypassed devices reduce resistance, causing high current. Loose connections increase resistance, causing low current. Ohm's Law in Series-Parallel Circuits - Current

The total current of the series-parallel circuits depends on the total resistance offered by the circuit when connected across the voltage source. The current flow in the entire circuit and it will divide to flow through parallel branches. In case of parallel branch, the current is inversely proportional to the resistance of the branch - that is the greater current flows through the least resistance and vice-versa. Then, the current will then sum up again after flowing in different circuit branch which is the same as the current source or total current.Ohm's Law in Series-Parallel Circuits - Voltage

The voltage drop across a series-parallel circuits also occur the same way as in series and parallel circuits. In series parts of the circuit, the voltage drop depends on the individual values of the resistors. In parallel parts of the circuit, the voltage across each branch are the same and carries a current depends on the individual values of the resistors.

If in case of circuit below, the voltage of the series resistance forming a branch of the parallel circuit will divide thevoltage across the parallel circuit. If in case of the single resistance in a parallel branch, the voltageacross is the same as the sum of the voltages of the series resistances.

CHECK YOUR UNDERSTANDING1. Which of the following will cause the current through an electrical circuit to decrease?

a. decrease the voltage

b. decrease the resistance

c. increase the voltage

d. increase the resistance

2. A certain electrical circuit contains a battery with three cells, wires and a light bulb. Which of the following would cause the bulb to shine less brightly?

a. increase the voltage of the battery (add another cell)

b. decrease the voltage of the battery (remove a cell)

c. decrease the resistance of the circuit

d. increase the resistance of the circuit

3. You have likely been warned to avoid contact with electrical appliances or even electrical outlets when your hands are wet. Such contact is more dangerous when your hands are wet (vs. dry) because wet hands cause ____.

a. the voltage of the circuit to be higher

b. the voltage of the circuit to be lower

c. your resistance to be higherd. your resistance to be lower

e. the current through you to be lower

4. If the resistance of a circuit were tripled, then the current through the circuit would be ____.

a. one-third as much

b. three times as much

c. unchanged

d. ... nonsense! There would be no way to make such a prediction.

5. If the voltage across a circuit is quadrupled, then the current through the circuit would be ____.

a. one-fourth as much

b. four times as much

c. unchanged

d. ... nonsense! There would be no way to make such a prediction.

EXERCISES1. If doubling the voltage a resistor doubles the current through the resistor then

a. the resistor value decreased

b. the resistor value did not change

c. the resistor value increased

d. it is impossible to determine the change in the resistor value

2. The voltage across a fixed value of resistance is increased in five times, what does the current do?

a. it increased by a factor of five

b. it decreased by a factor of five

c. it stays the same

d. not enough information

3. If the resistance in a circuit with constant voltage increases the current will

a. increase

b. decrease

c. stay the same'

d. not enough informationENRICHMENT1.A nine volt battery supplies power to a cordless curling iron with a resistance of 18 ohms. How much current is flowing through the curling iron?

2.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?3.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?

EVALUATION

After our discussion about the topic, you will find out how well you are able to comprehend the lesson.

Read the question below and give your answer appropriately.

1. An electric heater draws a 3.5 A from a 110 V source. The resistance of the heating element is approximately

a. 385 ohms

b. 38.5 ohms

c. 3.1 ohms

d. 31 ohms

2. The formula to find I when the values of V & R are known is

a. I = VR

b. I = R/V

c. V = IR

d. I = V/R

3. A resistor is connected across a 50V source. What is the current in the resistors if the color code is red orange, orange, silver?

a. 2 mA

b. 2.2 mA

c. 214 mA

d. 21.4 mA

4. Approximately how many milliamperes of current flow through a circuit with a 40V source and 6.8k ohm of resistance.

a. 27.2 mA

b. 59 mA

c. 5.9 mA

d. 590 mA

5. What is the voltage source for a circuit carrying 2A of current through a 36 ohms resistor?

a. 1.8V

b. 18V

c. 7.2V

d. 72VANSWERS:

1. D

2. D

3. B

4. C

5. DPREPARED BY:

MARIBETH S. NITRO Science Teacher

REFERENCES

1. Science and Technology IV Textbook

(SEMP)2. Conceptual Science and Beyond Physics

Writer: Dr. Jose M Andaya

3. http://www.indiabix.com/electrical-engineering/ohms-law/

Ohm's law states that the current through a conductor between two points is directly proportional to the potential difference across the two points. Introducing the constant of proportionality, the resistance, one arrives at the usual mathematical equation that describes this relationship:

where I is the current through the conductor in units of amperes, V is the potential difference measured across the conductor in units of volts, and R is the resistance of the conductor in units of ohm's. More specifically, Ohm's law states that the R in this relation is constant, independent of the current.

The law was named after the German physicist Georg Ohm, who, in a treatise published in 1827, described measurements of applied voltage and current through simple electrical circuits containing various lengths of wire. He presented a slightly more complex equation than the one above to explain his experimental results. The above equation is the modern form of Ohm's law.

In physics, the term Ohm's law is also used to refer to various generalizations of the law originally formulated by Ohm.