Electrostatics

Question 1

Coulombs constant

Answer 1

9 x 10^9 Nm² / C²

Question 2

£o =

Answer 2

£o = 8.85 x 10^-12 C² / Nm²

Question 3

£r =

Answer 3

£r = £med / £o
£r = Fo /Fmed

Question 4

Electrical field is always from ___ to ___

Answer 4

Positive to negative

Question 5

Zero point field

Answer 5

Similar charges: zero point field between them
Different charges: zero point field away from them
(zero point field is like the field of repellence)

Question 6

Flux

Answer 6

dot product of E and A
ø = EA(cosø)

Question 7

SI Unit of flux

Answer 7

Nm² / C

Question 8

Field due to infinite sheet of charges

Answer 8

E = ∂/2£o
∂ = Q/A so
E = Q/2A£o or
Emed = Q/2A£o£r

Question 9

Field due to oppositely charged plates

Answer 9

E = ∂/£o so
E = Q/A£o or
Emed = Q/A£o£r

Question 10

Capacitance

Answer 10

C = A£o/d
C = A£o£r/d

Question 11

Effect of medium on capacitance

Answer 11

Smaller distance makes it easier to induce charge so instead, a dialectric is added

Question 12

Energy stored in capacitor

Answer 12

U = ½CV²
U = Q²/2C
U = ½E²£o£rAd
and U = ½QV (dont use for relations)

Question 13

Series vs Parallel capacitors

Answer 13

Series = 1/C1 + 1/C2 + 1/C3 …
Parallel = C1 + C2 + C3 …

Question 14

For parallel capacitance

Answer 14

V = same
Q = different
Net capacitance is greater than greatest capacitance

Question 15

Potential difference (∆v)

Answer 15

∆v = w/q

Question 16

Electric potential energy =

Answer 16

∆U = ∆v x q

Question 17

Charging and discharging formulae

Answer 17

Charging: V = Vo (1-e^-t/RC)
Discharging: V = Vo e^-t/RC

Question 18

Time constant

Answer 18

Time constant = RC
It is the time required to deposit 63% of the charge

Question 19

When RC high

Answer 19

Charging/discharging slow

Question 20

How many time constants to almost fully charge

Answer 20

5 cycles (99.9%)