**Ohms Law**: Ohm’s Law states that the current flowing through a conductor is directly proportional to the potential difference applied across its ends, provided the temperature and other physical conditions remain unchanged. Mathematically it can be represented as,

Potential difference ∝ Current

V ∝ I

When the value of V increases the value of I increases simultaneously

V = IR

Where, V is Voltage in volts (V), R is Resistance in ohm (Ω) ,I is Current in Ampere (A)

**Resistance**

The resistance R of the wire of length l and cross sectional area A, can be defined as

$R = ρ {l \over A}$

Series Combination

Dimension of Resistance : R = [ML^{2}T^{-3}A^{-2}]

Combination of Resistance

Series Combination

R = R

_{1}+ R

_{2}+ R

_{3}

Parallel Combination

${1 \over R } + { 1 \over R_1} + { 1 \over R_1} + { 1 \over R_1} + { 1 \over R_1} $

**Calculating Different Parameters Using Ohm’s Law**

To find Voltage

$ V = I × R $

To Find Current

$ I = { v \over R }$

To Find Resistance

$ R = {V \over I}$

**Power Triangle**

To Find Power

$ P = I × V $

To find Voltage

$ I = {P \over V}$

To Find Current

$ V = { P \over I }$

**Electromotive Force (emf)**

Hence, emf can also be defined as the ratio of electrical power generated to the current, which a source delivers. The emf is measured in volts

$emf = { power \over current} $

### Electric Circuits

### Alternating Current

An alternating current (A.C.) is one which periodically changes in magnitude and direction. It increases from zero to a maximum value, then decreases to zero and reverses in direction, increases to a maximum in this direction and then decreases to zero

The alternating emf E at any instant may be expressed as

E = E_{o} sinωt

**Advantage of AC over DC**

• The generation of A.C. is cheaper than that of D.C.

• Alternating voltage can be easily stepped up or stepped down by using a transformer.

• A.C. can be easily converted into D.C. by rectifier. D.C. is converted to A.C. by an inverter.

• A.C. can be transmitted to a long distance without appreciable loss.