I Q t

I = current Q = net charge flowing t = time

1A 1C 1s

Unit: Q = Coulomb (C) I = Ampere (A) t = Second (s) Potential difference

Work done to move a unit charge from one point to another V W Q

Unit Volt 1 Volt

1 joule 1 coulomb 1V 1J C

1

Ohm’s law Current potential difference V I V = IR (R = resistance) Unit (R) 1 1V 1A

(Ohm)

Factors on which resistance depends 1. 2. R R l, when A and material constant l = length A, when l and material constant A = perpendicular cross-section

R R

l A l A

(

= resistivity)

Unit ( ) m Resistance in a series connection R = R1 + R2 + R3 + … + Rn Resistance in parallel 1 R 1 R1 1 R2 ... 1 Rn

Heating Effect of current Electric energy = VIt

Heat, H VIt I 2 Rt

Application Electric iron, toaster, fused wire Fused wire: a low-melting point wire connected in series with electric devices for safety. Electric power P VI I R

2

V2 R

Unit – 1 kWh = 3.6 × 106 J 1 W = 1V × 1A Definitions Potential difference: The potential difference between two separate points is defined as the work done to move a unit positive charge from one point to another.

Resistivity: Resistivity of a substance is equal to the resistance of a unit square of that substance. Law Ohm’ law: Under constant physical conditions (i.e., constant temperature, pressure etc.), the current flowing through a conductor is directly proportional to the potential difference across the conductor.

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