University:
University of Cambridge
Course:
0625 IGCSE | Physics
Academic year:

2023
Views:

337

Pages:

2
Author:

Deddy A.

Current Average current: The amount of charge that flows through an area, in a given time interval Chapter 17 Electric current, I & Resistance Current conventions Conventional current is defined to flow in the direction that positive charges flow. Lave = ΔΙ Instantaneous current The limit of the average current as the time interval goes to zero. Ilim A lave lim ΔΙΟ ΔΙ The units of current are Amperes (A), where 1 A = 1 C/s (Ampere Coulomb/second) Resistance Resistance: R: The ratio of the potential difference (across an element of a circuit) over the current (through that element). Δ R= I Resistance is measured in Ohms (D), where 101 V/A (Ohm Volt/ Amps). Ohm's law: The potential difference, AV, across an element of a circuit is equal to the product of the resistance, R, and the current, I, through that element. AVIR Elements that obey this relation are called "Ohmic". conductor that provides a specified Ohmic resistors resistance in a Ohmic resistors obey Ohm's law. AVIR Resistance of an Ohmic resistor: Increases with length, L Decreases with cross-sectional area, A. circult Slope- 30 W p is resistivity A good L conductors R=p(T) 60 W A = low p resistivity We represent resistors as *(-) charge flowing to the left (+) charge flowing to the right (w=J/s) P = power V= voltage V2 IxR ITV R P T P VR PV PR IR P P VV2 [= current (A) RP NON-Ohmic resistors DEC EPE AV R= resistance Circuits Podtive curse nawk from the positive to the negathe terminal of the batter Circuits are collections of electrically-connected objects, usually including a source of electrical energy (e.g. a cell) connected to elements that convert that energy into some other form of energy (e.g. a bulb) or, possibly, store it (e.g. a capacitor). 12V 12V Schematic figure Resis (4) terminal but e move (-)→(+) F always HIGHER potential EPET LEPE W T when going thru resistor (which absorbs the Energy) D Figure 17.11 Arruit ommuting of a battery and a vesistance R. Poi A is grooled (E aka volts) Electromotive Force (EMF) →potential diff. of a source when No current is lowing. source of energy for circuit, generated by bartery work done to drive I coulomb of charge around a complete circuit ε battery PD is only betw. 2 points! + b - terminal voltage potential diff. betw. terminals of a cell when current flowe d R VEMFIr terminal voltage voltage drop across internal resistor * < EMF when circuit on ble a cell has an internal resistance that is utilized once battery is Connected to a circuit = EMF when current is O aka open-circuit loltage warm every battery/power source has an internal resistance (r) leads to battery while in use AV = € - Ir AV = IR I = R+r