26.6
Ohm's Law
Many materials exhibit a simple relationship between the values of current, voltage, and resistance, known as Ohm’s law. The current that flows throug…
In 1827, a German physicist, Georg Simon Ohm, demonstrated Ohm's law experimentally.
Ohm's law states that the current passing through a material is directly proportional to the voltage across the device under constant surrounding conditions.
Any material that obeys Ohm's law is known as an ohmic material, whereas if it does not obey Ohm's law, it is known as a nonohmic material.
Consider another experimental setup to demonstrate Ohm's law, consisting of a resistor, power supply, switch, voltmeter, and ammeter. The voltage across the resistor is measured using a voltmeter, while the current in line with the resistor is measured using an ammeter.
When the resistor is connected to the power supply, the current flows in the clockwise direction, and the voltmeter and ammeter show positive readings. Conversely, when the leads of the power supply are switched, the current flows in the counterclockwise direction, resulting in negative readings.
A graph plotted between the voltage and current readings is found to be linear. The slope of the line gives the resistance, confirming the resistor to be an ohmic device.
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Q1: What is Ohm's law and who discovered it?
Ohm's law states that the current passing through a material is directly proportional to the voltage across the device under constant surrounding conditions. German physicist Georg Simon Ohm demonstrated this relationship experimentally in 1827, establishing that electrical current in a metal wire increases proportionally with applied voltage.
Q2: What is the difference between ohmic and nonohmic materials?
Ohmic materials obey Ohm's law, meaning current through them is directly proportional to applied voltage, producing a linear voltage-current relationship. Nonohmic materials do not follow this proportional relationship. Examples of non ohmic devices include diodes and transistors, which exhibit nonlinear current-voltage characteristics.
Q3: How is resistance determined from a voltage-current graph?
When voltage and current measurements are plotted on a graph for an ohmic material, the resulting line is linear. The slope of this line directly represents the resistance of the material, calculated as voltage divided by current. This graphical method confirms whether a device behaves as an ohmic conductor.
Q4: What instruments are used to measure voltage and current in Ohm's law experiments?
A voltmeter measures voltage and is connected in parallel with the resistor, while an ammeter measures current and is placed in series with the resistor. Together, these instruments allow researchers to collect paired voltage and current readings across different applied potentials to verify Ohm's law experimentally.
Q5: How does reversing the power supply polarity affect current direction?
When power supply leads are switched, the current direction reverses. If current initially flows clockwise, reversing the polarity causes it to flow counterclockwise. Both the voltmeter and ammeter readings change sign accordingly, demonstrating that current direction depends on the polarity of the applied voltage.
Q6: What experimental setup did Georg Ohm use to demonstrate his law?
Ohm's original 1827 experiment measured voltage and current through various simple electrical circuits containing different lengths of wire. His setup consisted of a resistor connected in series with a battery, a voltmeter in parallel with the resistor, and an ammeter in series. Multiple measurements at different voltages revealed the linear relationship now known as Ohm's law.
Q7: Why is the linear relationship between voltage and current significant?
The linear voltage-current relationship in ohmic materials allows engineers and physicists to predict and control electrical behavior predictably. This proportionality means resistance remains constant across different voltages, making ohmic materials ideal for circuit design and analysis. The consistency of this relationship validates Ohm's law as a fundamental principle in electrical theory.