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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 = [ML2T-3A-2]

Combination of Resistance

Series Combination

R = R1 + R2 + R3

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

$emf = { power \over current}$

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 = Eo sinωt

• 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.

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