Dr Pusey

www.puseyscience.com

Syllabus pointsCircuit analysis and design involve calculation of the

potential difference across, the current in, and the power supplied to, components in series, parallel, and series/parallel circuits

This includes applying the relationships for series components:

𝐼 = 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡𝑉𝑡 = 𝑉1 + 𝑉2 +⋯𝑉𝑛𝑅𝑡 = 𝑅1 + 𝑅2+. . . 𝑅𝑛

Learning goals

Be able to use the equations below to determine potential difference, current, power and resistance in series circuits

𝐼 = 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡𝑉𝑡 = 𝑉1 + 𝑉2 +⋯𝑉𝑛𝑅𝑡 = 𝑅1 + 𝑅2+. . . 𝑅𝑛

Apply your knowledge of electrical circuits to everyday situations to explain how they work

Series circuit The flow of charge (current) must flow through

devices sequentially

In a series circuit the current only has one path to follow

Current in a series circuit Current in a series circuit is the same everywhere

𝐼𝑇 = 𝐼1 = 𝐼2 = 𝐼3…

Same number of charges passing each point per second

Charge does not pile up, or get ‘used up’ by resistors

The actual amount of current varies inversely with the amount of overall resistance (higher the total resistance, lower the current)

Resistance in series circuit Total resistance of a series circuit is the sum of the

individual resistances𝑅𝑇 = 𝑅1 + 𝑅2 + 𝑅3…

More resistors = more overall resistance

Potential Difference in a series circuit Total potential difference of a series circuit is the sum of the

individual potential differences𝑉𝑇 = 𝑉1 + 𝑉2 + 𝑉3…

The total potential difference is shared between the components in series (but not shared equally, depending on resistance of components)

Example 1

A series circuit contains a battery with a voltage of 12 V, and three resistors with resistances of 𝑅1 = 1.00 Ω , 𝑅2 = 5.00 Ω and 𝑅3 = 15.0 Ω .

a) What is the total resistance of the circuit?

b) Calculate the current of the circuit

c) Calculate the voltage drop in each resistor, and show these add to equal the voltage output of the source

Example 1

A series circuit contains a battery with a voltage of 12 V, and three resistors with resistances of 𝑅1 =1.00 Ω , 𝑅2 = 5.00 Ω and 𝑅3 = 15.0 Ω .

a) What is the total resistance of the circuit?

Example 1

A series circuit contains a battery with a voltage of 12 V, and three resistors with resistances of 𝑅1 =1.00 Ω , 𝑅2 = 5.00 Ω and 𝑅3 = 15.0 Ω .

b) Calculate the current of the circuit

Example 1A series circuit contains a battery with a voltage of 12 V, and three resistors with resistances of 𝑅1 =1.00 Ω , 𝑅2 = 5.00 Ω and 𝑅3 = 15.0 Ω .

c) Calculate the voltage drop in each resistor, and show these add to equal the voltage output of the source

Example 2For the circuit pictured below calculate the:

a) total resistance

b) current

c) current through each resistor

d) voltage drop across each resistor

e) power dissipated in each resistor.

Example 2For the circuit pictured below calculate the:

a) total resistance

Example 2For the circuit pictured below calculate the:

b) current

c) current through each resistor

Example 2For the circuit pictured below calculate the:

d) voltage drop across each resistor

Example 2For the circuit pictured below calculate the:

e) power dissipated in each resistor.

Context – Christmas lights Christmas tree lights used to be connected in a series

circuit. Why have they changed them to parallel circuits?

Series Circuit – sum up Current = constant, same at all points of circuit

Total resistance = sum of individual resistances𝑅𝑇 = 𝑅1 + 𝑅2+. . .

Potential difference = shared among the components (but not shared equally)

𝑉𝑇 = 𝑉1 + 𝑉2 + 𝑉3…

ResourcesAV

Khan Academy - Circuits (part 1) (11:40)

Khan Academy - Circuits (part 2) (11:08)

Khan Academy - Circuits (part 3) (12:21)

Khan Academy - Circuits (part 4) (7:07)

Simulation

PhET – DC circuit construction kit