Do now: NCEA 2006

1) Calculate the total capacitance

2) Calculate the total charge

stored in the capacitors

3) Calculate the total energy

stored in the capacitors

4) Calculate the voltage across the 4.00 μF capacitor

Friday, April 21, 2023

QVE 21

Q CV 21 CCCT

21

111

CCCT

Sketch and explain these graphs for Sketch and explain these graphs for chargingcharging a capacitor a capacitor

It’s easy at first because the It’s easy at first because the plates are empty, but as plates are empty, but as they fill the stored charge they fill the stored charge starts to repel further charge starts to repel further charge and the rate decreasesand the rate decreases

Voltage across capacitor

t

Vmax

Current in circuit

t

Imax

As the rate of charge As the rate of charge movement decreases, movement decreases, the current flow in the the current flow in the circuit decreasescircuit decreases

Sketch and explain these graphs for Sketch and explain these graphs for dischargingdischarging a capacitor a capacitor

The voltage will be at a max to The voltage will be at a max to begin with, drops quickly at first begin with, drops quickly at first (due to maximum repulsion), but (due to maximum repulsion), but then more slowly as fewer then more slowly as fewer charges remain on the capacitor.charges remain on the capacitor.

The current will be large The current will be large at first, but decrease as at first, but decrease as potential left to “push” potential left to “push” decreasesdecreases

Voltage across capacitor

t

Vmax

Current in circuit

t

Imax

Time constant

Is the time it takes for V (or I)

to change by 63% of its value

If C is large, more charge can be stored, so takes longer to fill/empty.

More R in the circuit means smaller current, so longer to fill/empty.

RC

A cap is considered fully

charged or discharged

after 3 time constants

Skim read p229 – 233

Look at Example on p231

*** Do Activity 14C ***