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cell energy ☺ electron lamp

Coulomb of charge (electrons) Think of it as a “bag of electrons” (containing 6000000000000000000 electrons!) ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺ ☺

I’m counting how many coulombs of electrons go past me every second Current I’m counting how many coulombs of electrons go past me every second ☺ ☺ ☺ The rate of flow of electric charge (number of Coulombs flowing past a point in the circuit every second). I = ΔQ/Δt ☺ ☺ A ☺ ☺ ☺ ☺ ☺ ☺ 1 Amp = 1 coulomb per second

In a series circuit Current is the same at any point in the circuit

In a parallel circuit The current splits (total current stays the same) 2.5 A 2.5 A 1.25 A 1.25 A

Voltage(emf) ☺ V I’m checking the difference in energy (per coulomb) between the 2 red arrows 1 Volt = 1 Joule per coulomb

Voltage (p.d.) ☺ I’m checking the difference in energy (per coulomb) before and after the lamp V 1 Volt = 1 Joule per coulomb

In a series circuit The sum of the p.d.s across the lamps equals the emf across the cells 9 V 3 V 3 V 3 V

In a parallel circuit In a simple parallel circuit, p.d. across each lamp equals the e.m.f. across the cells 5 V 5 V 5 V

Resistance Measures how difficult it is for current to flow. Measured in Ohms (Ω) A V Resistance = voltage/current R = V/I

Ohm’s Law V = IR V R I X

Adding resistances

In series?

Adding resistors in series

Examples

Adding resistors in parallel

Adding resistors in parallel

Examples

Other examples

Resistance R is proportional to the length of wire – WHY? R α L R is inversely proportional to the cross sectional area of wire – WHY? R α 1/A R depends on the type of material – WHY?

Resistivity R = ρL A where R = resistance in Ohms L = Length of conductor in metres A = cross sectional area of conductor in m2 ρ = resistivity of the material in Ohms.meters