Electricity chapter 9 & chapter 10

CIE A-LEVEL

definition of electric current

the flow of charge carriers

potential difference definition

the energy transferred per unit charge between 2 points in a circuit (V=W/Q)

power equations

P = VI, P = I²R, P=V²/R

what is the charge on charge carriers

1.6×10^-19

how to find number of electrons

N = Q/e

Definition of power

energy transferred over time (P=E/t)

What is the product of power and time

energy : E = VIt

definition of resistance

a measure of how difficult it is for charge carriers to pass through a component : V=IR

what happens to the resistance of a filament lamp as the current increases

as current increases, the metal wire heats up causing the temperature to increase and therefore the resistance increases

state ohms law

Current is directly proportional to voltage

Formula for resistivity

p = RA/ L

what happens to resistances of an LDR as light increases

resistance decreases as light intensity increases

what happens to the resistance of a thermistor as temperature increases

as temperature increases, resistance decreases because current increases

what is emf

electromotive force is the energy transferred by a cell per column of charge that’s passes through

(emf = E/Q)

what is internal resistance caused by

caused by electrons colliding with atoms inside the battery. this causes some energy t be lost before electrons even leave the battery

so emf is …

the product of total resistance and the current of the circuit because V = IR

therefore emf is the sum of terminal p.d and lost volts

emf vs pd

• E.m.f.: energy given to each coulomb by the source.

• P.d.: energy transferred from each coulomb between two points.