Question

Which of the following is an ohmic conductor?
A. Germanium
B. Silicon
C. Carbon
D. Silver

Answer 1

The answer relates to the use of the concept behind ohmic conductors and the criteria under which they are said to be called so. The conditions under which ohm’s law is applicable needs to be known in order to determine whether the given options are an example of ohmic conductors or an example of non-ohmic conductors. Each of the given options are taken separately and categorized into either ohmic or non-ohmic conductors to determine the correct answer.

Complete answer:
In order to find out which of the given options is an ohmic conductor we first need to know the concept behind ohmic conductors and the principle behind ohm’s law. Let us first define conductors. Conductors are materials that allow the flow of charges or the flow of current through them. Hence the resistivity or the ability to resist the flow of current will be minimum in these types of materials.

Ohm's law is said to state the relationship between electric current and voltage on the basis of experimental observations. Ohm's law states that the current flowing through a conductor is directly proportional to the potential difference applied across it, when temperature and other physical conditions are kept constant. It is given by the equation: $V = IR$.

Since current is said to be directly proportional to the potential difference produced, the graph drawn to depict the relation between the two quantities will be a linear graph and will vary linearly with time. This means that when one quantity either current or voltage increases by a certain amount the other quantity also increases by the same amount. Hence a straight-line graph is produced. This is the condition which the conductors must follow in order to obey Ohm's law.

Knowing this, let us define ohmic conductors. Ohmic conductors are conductors which obey ohm’s law wherein the relationship between current and voltage remains linear at all conditions and the resistance is independent of the current through the conductor. The V-I graph remains a straight line graph.

However, the law does not hold true for all metals and nonmetals. The conductors which do not obey the ohm’s law are called non-ohmic conductors and the resistance of these conductors are said to be unstable even at a given temperature.

Let’s look at each of the given options in detail. Metallic conductors are said to disobey ohm’s law. Carbon is an example of a metallic conductor. When large amounts of current pass through metallic conductors they get heated up increasing the resistance and the V-I graph becomes a non-linear one disobeying ohm’s law. Since it fails to obey ohm’s law it comes under the category of non-ohmic conductors. Hence option (C) is rejected.

P-N junction diodes made up of semiconductor materials are also said to disobey ohm’s law. We are all well aware that Germanium is widely used in semiconductor materials. The semiconductors have a property wherein for a certain voltage condition, that is, for a cut-off voltage there is a sudden shoot up of current and as far as the minority charges are concerned, very little current flows for a fairly high negative voltage. This means that the graph will not be linear and hence they are said to be non-ohmic conductors. Hence option (A) is rejected.

As mentioned earlier, we know that P-N junction diodes are made up of semiconductor materials. The main material that is often used to make the semiconductor materials is Silicon. The atoms of the semiconductor are made up of Silicon for making p-type materials. Hence Silicon is proved to be an example for non-ohmic conductors. Hence option (B) is rejected.

The only option left is option (D) which is Silver. Silver is proved to come under the category of ohmic conductors because it is a really good conductor of electricity and there are many applications wherein electrical wires are made of silver in order for current to pass through it smoothly as it is a good conductor. It also obeys ohm’s law and exhibits a linear V-I graph.Thus option (D) is an example for ohmic conductors.Hence, silver is an example of ohmic conductors.

Therefore, the correct option is option D.

Note: Silver is known to be the best conductor of electricity but Copper and Aluminum metals are said to be widely used in making electrical wires because of their cost which is really cheap in comparison to silver which is said to be highly expensive. Some materials are said to undergo a phenomenon known as superconductivity where there is a complete loss of resistivity by certain metals or alloys when they are cooled below a certain temperature.