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!
