Capacitance

Question 1

State practical uses of capacitors in circuits.

Answer 1

• provide time-delay
• block DC
• in oscillator/tuning circuits
• power smoothing in rectified AC
• protection against power spikes/surges

Question 2

Define capacitance.

State it’s unit.

Answer 2

Ratio of charge “stored” by a capacitor to the p.d. across it. (NB: Capacitors store energy, not charge.)

Unit of C = Farad (coulombs per volt)

Question 3

Define capacitance of a parallel plate capacitor.

Answer 3

Ratio of charge stored on one plate to the p.d. between the plates. (N.B. 2nd plate is charged via induction)

C is prop. to area of plates.
C is inv. prop. to distance between plates.