23 Capacitors

Question 1

capacitance

Answer 1

the charge stored per unit pd of a capacitor. the unit of capacitance is the farad (F), equal to 1 coulomb per volt. for a capacitor of capacitance C at pd V, the charge stored Q=CV

Question 2

time constant

Answer 2

the time taken for a quantity that decrease exponentially to decrease to 0.37 (1/e) of its initial value. for the discharge of a capacitor through a fixed resistor, the time constant = resistance * capacitance

Question 3

Dielectric

Answer 3

material that increase the capacity of a parallel-plate capacitor to store charge when placed between the plate of the capacitor. polythene and waxed paper are examples of dielectrics

C=AEoEr / d

Question 4

polarised

Answer 4

the positive charge and the negative charge of a polarised molecule are displaced in opposite direction

Question 5

equation of capacitance

Answer 5

C = Q/V

Question 6

capacitors are used in

Answer 6

smoothing currents
back-up power supplies
timing circuits
pulse-producing circuits
tuning circuits
filter circuits

Question 7

energy stored in a capacitor

Answer 7

E = 1/2 QV

E= 1/2 Cv^2

E=1/2 Q^2 / C
(area under the graph)

Question 8

thundercloud

Answer 8

1/2 QEd

Question 9

To find the initial current of a capacitor

Answer 9

I = V ./ R

Question 10

relative permittivity

Answer 10

permeability is the measure of the ability of a material to support the formation of a magnetic field within itself

Question 11

Dielectric constant

Answer 11

Dielectric constant, property of an electrical insulating material (a dielectric) equal to the ratio of the capacitance of a capacitor filled with the given material to the capacitance of an identical capacitor in a vacuum without the dielectric material.

Question 12

time constant

Answer 12

RC

Question 13

time to have

Answer 13

T= 0.69 RC

Question 14

capacitor discharge

Answer 14

Q = QoE ^-1/rc

Question 15

capacitor charging

Answer 15

Q = Qo(1-E ^-1/rc)