Potential Dividers and Internal Resistance

Ratio of p.ds and resistors in potential dividers

the ratio of p.d.s is the same as the ratio of the resistors

Equation for ratio of voltages and resistances in potential divider circuit

V1/V2 = R1/R2

Potential divider equation

Vout = R2/(R1+R2) x Vin

What does R2/(R1+R2) represent

the ratio of the resistance R2 to the total resistance R1+R2

Why is some energy ‘lost’ when there is a current in a power source

whenever there is a current, work has to be done by the charges as they move through the power source ∴ some energy is transferred into heat

terminal p.d

the p.d at the terminals of the power source

lost volts (Ir)

the difference between the actual emf and the terminal p.d

equation linking emf, terminal p.d and lost volts

E = V + Ir

Relationship between emf and terminal p.d when current is very small

E = V

Equation for the straight line on a V-I graph

E = V + Ir

y = mx + c

V = -rI + E