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Ohms Law

Electricity I - Concepts

Resistance Depends on Length

Resistance Depends on Area of Cross Section

Resistivity

Class - 9th Aus Edu Subjects

Concept Explanation

Ohms Law

We all have experienced the situation that when a torch is used for several weeks, its light becomes dim. We say that its cells have become weak.This means that the potential difference has droped to a smaller value because the chemicals have been used up in the chemical reactions. As the potential difference has dropped so less current flows through the bulb, and hence produces less light. So, we can say that the electric current passing through the circuit depends on the potential difference applied across it. The larger is the potential difference, the larger is the current. This relationship between potential difference and current was first discovered by a German physicist Georg Simon Ohm (1787-1854) and is stated by the law named after him

Ohm's Law states that the current passing through a conductor is directly proportional to the potential difference between its ends, provided the physical conditions such as temperature of conductor remain unchanged.

He further observed that as we increase the potential the current increases, so we can state that the

i.e., $large Vinfty I$ or $large V= RI$

where R is a constant which is called resistance of the material.

Unit of resistance

$large R=frac{V}{I}=frac{volt}{ampere}=ohm(Omega )$

The SI unit of resistance is ohm $large (Omega )$ .

If I = 1 Ampere, V = 1 Volt, then R = 1 $Omega$ .

The resistance of a conductor is 1 ohm if a potential difference of 1 volt is produced across its ends when 1 ampere of the current flows through it.

The conductors, which obey the Ohms law are called the ohmic conductors or linear resistances. All metallic conductors (such as silver, aluminium, copper, iron , etc,) are the Ohmic conductors or linear resistances.

The conductors, which do not obey the Ohms law are called the non-Ohmic conductors or non-linear resistances. Examples are, diode valve, transistors, electrolyte, etc.

Illustration: A 5 V battery is connected to a 10 $Omega$ resistance. Calculate the amount of current flowing through the circuit.

Solution: It is given that

V = 5 V

R = 10 $Omega$

To find I =?

According to Ohm's Law

V = IR

$Rightarrow ;I= frac{V}{R}= frac{5}{10}= 0.5 ;A$

Hence a current of 0.5 A flows through the circuit.

Sample Questions

(More Questions for each concept available in Login)

Question : 1

If the temperature of a conductor is increase, its resistance will _______________
A. Not increase	B. Increase	C. Decrease	D. Change according to the whether
Right Option : B
View Explanation

Question : 2

Write the following steps in a sequential order to determine the number of electrons flowing through the cross section of a wire in a time 't' when a potential difference of V volts is applied across a wire of resistance R. (A) Determine the number of electrons 'n' by using the relation ,i=ne/t. (B) Note the values of V, R, t and charge of an electron 'e'. (C) Determine the electric current i following through the wire as i= $frac{V}{R}$
A. B A C	B. B C A	C. A B C	D. A C B
Right Option : B
View Explanation

Question : 3

A 160-V battery is connected to a lamp of resistance $large 4Omega$ . Calculate current through the lamp.
A. 12 A	B. 40 A	C. 14 A	D. 4 A
Right Option : B
View Explanation