Elect!city Conventional Current : Flow from + to - (opposite of the electron flow) Electron Flow : the flow of electrons from - to +, making a current. Conduction/free/delocalised electrons : the particles which allow a metal to conduct an electric current. Electrolyte : A solution which conducts electricity because it has charge carriers Charge Carriers : Any charged particle which contribute to an electric current. Can be electrons, protons, or ions. 1 Coulomb is the amount of charge which flows past a point in a circuit in a time of 1 s when the current is 1 A. Elementary Charge : the charge 1 electron has. e = 1.6 × 10 −19 C 1C = 6.25 × 1018 electrons Equation Charge = Current x Time Q = It Kirchkoff’s First Law The sum of the currents entering any point in a circuit is equal to the sum of the currents leaving that same point. Equation I = Anev I = Current A = cross-sectional area n = Number density v = mean drift velocity Number density : Number of conduction electrons per unit volume (in m −3 ) Mean Drift Velocity : The average velocity at which the electrons travel (m/s) Electric force causes the electrons to move towards + end of battery. Electrons randomly collide with the metal ions. Journey along metal is very haphazard, so its called drift velocity. Anastasya’s Notes : <http://highschoolnotesinternational.wordpress.com/> I = Anev I = m 2 × m −3 × C × ms −1 m3 × C I= 3 m ×s I =C/s I= Q ,QED. t Resistance Resistance : a material's opposition to the flow of electric current; measured in ohms. Dependant on voltage and current. V R= I I-V Characteristics In a metal resistance wire/resistor, Graph is a straight line, passes through origin I ∝V Wire has a constant resistance In a filament Lamp, Graph is a curve. Gradient increases as I increases As current increases, metal filament gets hotter and R increases In a Diode, There’s almost no current when V is is applied in reverse. Reverse diode have very high resistance In the forward direction, current increases very rapidly Forward diode have very low resistance Anastasya’s Notes : <http://highschoolnotesinternational.wordpress.com/> Ohm’s Law For a metallic conductor at constant temperature, the current in the conductor is directly proportional to the potential difference across its ends. Thermistors -> Components which are designed to have resistance which rapidly changes with temperature. 2 types : Negative Temperature Coefficient (NTC) ! The resistance decreases as temperature increases. Positive Temperature Coefficient (PTC) ! The resistance rises abruptly at a certain temperature Resistance and Temperature At low temperatures, The particles vibrate in place Electrons flow relatively freely. At high temperatures, Ions vibrate more Electrons collide more with the ions, obstructing the flow Resistance is higher. Resistivity Resistivity : A measure of how strongly a material opposes the flow of electric current. Depends on the material, not affected by V or I. resis tan ce = R= ρL A ρ= RA L resistivity × length cros − sectional _ Area -> Resistivity increases with temperature. Voltage Potential Difference : when charges lose energy by transferring electrical energy to other forms. (across a resistor, in external circuit) Electromotive force : when charges gain electrical energy from a power supply. (across battery) Anastasya’s Notes : <http://highschoolnotesinternational.wordpress.com/> Energy and Power Potential difference Potential _ difference = V= Energy _ lost _ by _ ch arg e ch arg e Work Q 1 volt = 1 joule/coulomb. Power Power = P= Energy _ transferred time _ taken W t Power and Current So, put the 2 together: W = VQ VQ P= t Q P =V t P = VI Power = p.d. × current Power and Resistance P = VI,V = IR P = I 2R V2 P= R Calculating Energy Since _ P = VI,W = Pt W = IVt Energy Transferred = Current x Voltage x Time Anastasya’s Notes : <http://highschoolnotesinternational.wordpress.com/> EQUATIONS USED e = 1.6 × 10 −19 C 1C = 6.25 × 1018 electrons Q = It I = Anev V R= I RA ρL R = L or A Work V= Q W P= t ρ= P = VI P = I 2R V2 P= R W = IVt Anastasya’s Notes : <http://highschoolnotesinternational.wordpress.com/>