Do now:

A very keen student wants to make a 1.0F capacitor,

using parallel metal plates 1.0mm apart in air.

What size plates are needed?

Wednesday, April 19, 2023

Last week we covered:

LO2 - 4) Kirchoff’s laws and internal resistance

This week we are learning:

LO5 - 9) Capacitors

- in series and parallel - time constant for charging and discharging

Learning Outcomes:

Homework:

1) NZQA Kirchoff (Q1-5): please mark

2) NZQA Capacitor (Q1-7): due 19 Aug

Practical 1:

Practical 2:Connect two capacitors is parallel and verify:

Connect two capacitors in series and verify:

Measure capacitanceChange area then

plate separationAdd a dielectric

(e.g. wooden rulers) and calculate

woodwood

air

C

C

1 2 ...PC C C

1 2

1 1 1...

SC C C

2.0 6.0wood

Be aware:

Electrolytic capacitors:

- two rolled aluminium sheets

- when charged, a very thin layer of Al2O3 forms on the positive plate which acts as the dielectric.

- called “polar” because you must connect the terminals the right way round

- high capacitance > 5μF

Wednesday, April 19, 2023

“Non-polar” capacitors:

- two rolled aluminium sheets

- with plastic or ceramic in between as the dielectric

- smaller capacitance < 5μF

- if you connect an electrolytic capacitor with the wrong polarity, the dielectric layer becomes a conductor!