What is the fundamental requirement for a conductor to obey Ohm's Law?

The current through the conductor must be directly proportional to the potential difference across it. This relationship only holds if physical conditions, specifically temperature, remain constant.

How does the $I-V$ graph of an Ohmic conductor differ from a Non-Ohmic conductor?

An Ohmic conductor produces a straight line that passes through the origin, indicating constant resistance. A Non-Ohmic conductor produces a curved line, indicating that resistance changes as the current or voltage changes.

Why does a filament lamp not obey Ohm's Law?

As current increases, the filament heats up. This increase in temperature causes the metal ions to vibrate more, increasing the resistance and resulting in a non-linear $I-V$ relationship.

If you have an $I-V$ graph (Current on y-axis, Voltage on x-axis), how do you find the resistance?

The resistance is the reciprocal of the gradient ($R = 1/\text{gradient}$). A steeper gradient represents a lower resistance.

What is a common mistake when calculating resistance from a graph with axes labeled in $mA$ and $V$?

Forgetting to convert milliamperes ($mA$) to Amperes ($A$) before using the formula $R = V/I$. This results in a resistance value that is 1000 times smaller than the actual value.

What happens to the current in a circuit if the resistance is tripled while the voltage remains constant?

According to $I = V/R$, the current is inversely proportional to resistance. Therefore, tripling the resistance will cause the current to decrease to one-third of its original value.

How should a voltmeter and ammeter be connected to measure the resistance of a component?

The ammeter must be connected in series with the component to measure the current flowing through it. The voltmeter must be connected in parallel across the component to measure the potential difference.

What does a horizontal line on a Resistance vs. Potential Difference ($R-V$) graph indicate?

It indicates that the resistance is constant regardless of the voltage applied, which is the characteristic behavior of an Ohmic conductor.

When comparing two $I-V$ graphs, how can you tell which resistor has a higher resistance?

The graph with the shallower (less steep) gradient has the higher resistance. This is because for the same potential difference, less current is able to flow through it.

What is the definition of an Ohm in terms of other SI units?

One Ohm is defined as the resistance of a conductor such that a potential difference of one Volt applied across it produces a current of one Ampere ($1 \, \Omega = 1 \, V/A$).

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Ohm's Law

Summary

Ohm's Law describes the fundamental relationship between electric current, potential difference, and resistance in a conductor. It states that the current flowing through a conductor is directly proportional to the potential difference across it, provided physical conditions like temperature remain constant.

1. Definition & Core Concepts

Ohm's Law is a principle stating that the current ( $I$ ) through a conductor between two points is directly proportional to the potential difference ( $V$ ) across the two points.
This proportionality holds true only if the temperature and other physical conditions of the conductor remain unchanged, as temperature fluctuations can alter the material's internal resistance.
Resistance ( $R$ ) is defined as the opposition to the flow of electric current, effectively acting as a measure of how difficult it is for charge carriers to move through a material.
The unit of resistance is the Ohm ( $\Omega$ ), which is defined as one volt per ampere ( $1 \, \Omega = 1 \, V/A$ ).

A standard circuit diagram showing a power source, a resistor, an ammeter in series, and a voltmeter in parallel across the resistor.

2. Mathematical Foundation

3. Graphical Analysis

4. Key Distinctions: Ohmic vs. Non-Ohmic

5. Exam Strategy & Tips

6. Common Pitfalls & Misconceptions