ch23 - capacitance

Question 1

capacitors used to

Answer 1

store energy in electrical and electronic circuits

Question 2

parts of capacitor

Answer 2

. two metal plates
. two leads/wires
. insulating material called dielectric between plates

Question 3

dielectric

Answer 3

name of insulating material

Question 4

to charge capacitor

Answer 4

. connect to voltmeter
. ammeters give identical readings

Question 5

when is capactor fully charged

Answer 5

. current stops
. when pd across capacitor = emf of supply

Question 6

positive metal plate terminal

Answer 6

. same side as positive battery terminal
. electrons flow from that to positive battery terminal

Question 7

electron flow and conventional current

Answer 7

opposite directions

Question 8

both metal capacitor plates stored

Answer 8

. equal and opposite charges

Question 9

Q for capacitor

Answer 9

magnitude of charge on each plate

Question 10

to make capacitor plates store more charge

Answer 10

higher emf supply

Question 11

capacitance

Answer 11

the capacitance of a capacitor is the charge on the plates of the capacitor per unit potential difference across the plates

symbol C

Question 12

C = Q/V

Question 13

farad

Answer 13

the unit of capacitance
1F = 1C V^-1

usually measured in pico, nano and microfarads

Question 14

capacitor markings

Answer 14

. positive terminal
. highest safe voltage

Question 15

to charge capacitor

Answer 15

work must be done in moving electrons from one plate to another

Question 16

more charge

Answer 16

. more repulsion
. more repulsion between electrons
. more work done

Question 17

W = QV

Question 18

energy stored

Answer 18

area under V Q graph
W = 0.5 QV

Question 19

work done by capacitor

Answer 19

W = 0.5 Q²/C

derived from
W = 0.5 QV
W = 0.5 CV²
W = 0.5 Q²/C

Question 20

capacitors in parallel

Answer 20

C total = C1 + C2

Question 21

C total = C1 + C2 deviation (parallel)

Answer 21

Q = Q1 + Q2
Q = VC1 + VC2
Q = V(C1 + C2)
C total = C1 + C2

Question 22

capacitors in series

Answer 22

1/C total = 1/C1 + 1/C2

Question 23

1/C total = 1/C1 + 1/C2 derive (series)

Answer 23

V = Q/C total
V = V1 + V2

Q/C total = Q/C1 + Q/C2
1/C total = 1/C1 + 1/C2

Question 24

capacitors vs resistors

Answer 24

reciprocal is:
. parallel resistors
. series capacitors

Question 25

when two capacitors are connected

Answer 25

charge is shared between them

Question 26

when sharing charge between capacitors

Answer 26

energy is lost as heat

Question 27

to calculate total energy when sharing charge between capacitors

Answer 27

Q = VC E initial = 0.5CV² C total V = Q/C total energy = 0.5 Ctotal V²

Question 28

capacitance of spherical bodies

Answer 28

V = Q/ 4* pi *Epsilon0* r C = Q/V

Question 29

to discharge capacitor

Answer 29

connect to resistor current time graph curves down, exponential decay

Question 30

exponential decay

Answer 30

the decrease of a quantity where the rate of decrease is proportional to the value of the quantity

Question 31

exponential decay formula

Answer 31

x = x0 * e^-ky . y is independent variable . k and x0 are constants . e is exponential function (randomly occurinf number with value)

Question 32

less resistance

Answer 32

faster discharge of capacitor

Question 33

time constant

Answer 33

. equal to RC . equal to the time it takes fkr the currenr in a circuit to fall to 1/e of the initial current, where e is exponential function

Question 34

T = RC

Answer 34

time constant for capacitor discharging

Question 35

exponential decay of charge on a capacitor

Answer 35

I = I0 exp (-t/RC) Q = Q0 exp (-t/RC) V = V0 exp (-t/RC)