Which one of the following is an ohmic conductor that obeys Ohm law over a wide range of voltages?

Introduction / Context:
Ohm law states that the current through a conductor is directly proportional to the potential difference across it, provided physical conditions such as temperature remain constant. Materials that follow this linear relationship between voltage and current over a wide range are called ohmic conductors. Identifying examples of ohmic versus non ohmic conductors is important in basic electricity and electronics.

Given Data / Assumptions:

• The question asks for an ohmic conductor.
• Options include germanium, silicon, carbon, silver, and selenium.
• We assume normal room temperature and typical circuit conditions.
• We rely on the distinction between metals and semiconductors in their conduction behaviour.

Concept / Approach:
Metals such as copper, silver, and aluminium typically obey Ohm law reasonably well over a wide range of applied voltages, showing a straight line current voltage graph. In contrast, semiconductors like germanium, silicon, and selenium have nonlinear current voltage characteristics that depend strongly on temperature and applied voltage, so they are considered non ohmic. Carbon in the form of graphite can show approximately ohmic behaviour in some cases, but the most standard textbook example of an ohmic conductor among the options given is a metal such as silver.

Step-by-Step Solution:
Step 1: Recall that ohmic conductors have a constant resistance, so the ratio of voltage to current remains constant as voltage changes. Step 2: Metals like silver, copper, and aluminium consist of a lattice of positive ions with free electrons that move under an electric field. Step 3: Within ordinary operating ranges, these metals show a linear relation between current and voltage, satisfying Ohm law. Step 4: Semiconductors such as germanium, silicon, and selenium have charge carriers whose numbers and mobility change strongly with voltage and temperature, leading to nonlinear behaviour. Step 5: Graphite is a form of carbon and can be used as a resistor, but variability in structure and temperature effects make it a less clear standard example. Step 6: Among the options, silver metal is clearly an ohmic conductor and is the best answer.

Verification / Alternative check:
Experiments in physics laboratories often use metallic wires such as nichrome or copper to verify Ohm law by plotting current against voltage and obtaining a straight line graph. Semiconducting diodes made from silicon or germanium show curved current voltage plots, demonstrating non ohmic behaviour. Silver is known as one of the best electrical conductors and behaves like other metals in showing near linear Ohm law behaviour over usual voltage ranges. These observations support the conclusion that silver is an ohmic conductor.

Why Other Options Are Wrong:
Germanium: A semiconductor with nonlinear current voltage characteristics, used in diodes and transistors.
Silicon: The most widely used semiconductor in electronics, showing non ohmic behaviour in devices like diodes and integrated circuits.
Carbon (graphite): Can conduct electricity but often shows deviations from ideal Ohm law due to structure and temperature effects; not the standard textbook example.
Selenium: A semiconductor used in photoelectric cells and rectifiers, also non ohmic.

Common Pitfalls:
Students may mistakenly select silicon or germanium because they are familiar from electronics, forgetting that semiconductors rarely show a simple linear relationship between current and voltage. Another pitfall is to think that any conductor is automatically ohmic. To answer correctly, remember that metals are typical ohmic conductors, while semiconductors and many other materials are non ohmic. Silver, as a classic metal, is therefore the correct choice.

Final Answer:
Silver metal is an ohmic conductor that obeys Ohm law over a wide range of voltages.