Discovering Ohm’s Law. With Great Power Comes Great Current Squared Times Resistance

Content

Overview

Ohm’s Law

Sample Problem 2.0

Activity 2: With great power comes great current squared times resistance

Procedure:

Observations:

Results and Analysis

Observations:

Application

References

Overview

In exploring the world of electricity it is essential to start by understanding the basic concepts of current, resistance, and voltage or potential difference. These three key building blocks are required to manipulate and investigate electricity. Unseen concept like this can be detected by the use of measuring tools such as a ammeter, voltmeter and ohmmeter. This will help the students visualize what is happening with the charge in a system. The relationship between voltage, current and resistance will be explained thoroughly in this learning booklet.

1. Define Ohm’s law;
2. Use Ohm’s law to calculate current, voltage and resistance in simple electric circuits;
3. Determine the current, voltage and resistance using measuring devices;
4. Calculate the power of a circuit given any two of the three electrical quantities – current, voltage and resistance.

Ohm’s Law

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In 1827 a German physicist, Georg Simon Ohm experimentally established the relation among electric current, resistance and potential difference in an electric circuit. He found out that the current passing through conductor varies directly as the potential difference applied at its ends and inversely as the resistance of the conductor. This statement is called Ohm’s law and may be applied to the whole circuit or to a particular part of a circuit.

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Applied to the whole circuit IT= V/RT , where IT is the total current, V is the voltage, and RT is the total resistance of the circuit.

Applied to a portion of the circuit, I=V/R where I is the current in ampere (A) passing through that part of the circuit, V is the potential difference in volts (V), and R is the resistance in ohms (Ω) of the same part of the circuit.

While we can calculate the current, potential difference and resistance mathematically, there are devices which give us measurements of the these three quantities in a circuit. The three devices are:

Sample Problem 2.0

1. How much current flows through a lamp with resistance 85Ω when it is connected to a 220-V outlet?

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2. What is the resistance of a lamp which allows 0.7 A current when 110.0 V is applied to it?

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3. While repairing an electric bulb socket, an electrician gets a mild shock when a current of 0.004 A passes through him. The same electrician is killed by a current of 0.16 A when he turned on an electric bulb while taking a bath. The voltage in each situation is equal to 120 V. Find the resistance of the electrician in each situation.

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Note: The human body’s resistance to current is in the order of 5000 000 Ω when the skin is dry. This resistance decreases when the skin is wet which can go as low as 100Ω when it soaked with saltwater. This is because ions in saltwater are current carriers and readily conduct electric charge.

The lie detector measures several parameters. One of which is skin conductivity or skin resistance. This based on the premise that a person sweats more when under stress and thus affects his or her resistance to current.

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