Circuits

Question 1

Current equation

Answer 1

I = Q/t

I = current
Q = charge
t = change in time

• SI unit = ampere (1 A = 1 C/s)
  C = coloumb

Question 2

Resistance equation

Answer 2

R = pL/A

R = resistance
p = resistivity (resistivity is the intrinsic resistance to current flow of a given material --> SI unit = ohm-meter)
L = length of resistor
A = cross-sectional area of resister

Question 3

Ohm’s Law equation

Answer 3

V = IR

V = volts
I = current (SI unit = amps)
R = resistance (SI unit = ohms)

Question 4

Power of Resistor equation

Answer 4

P = IV

P = power
I = current
V = voltage

*** NOTE! remember that you can use P=IV and V=IR together to figure out problems.

*** remember, P = W/t (work/time) = deltaE/t (change in energy/time)

Question 5

Capacitance equation

Answer 5

C = Q/V

C = capacitance (SI Unit = farad)
Q = charge (SI unit = coloumb)
V = voltage

Question 6

What does a dielectric material do to capacitance when inserted between a two-plate capacitor?

Answer 6

Capacitance INCREASES by a factor called the dielectric constant.

Equation: C’ = kC
(C’ is the new capacitance; k is the dielectric constant)

(Remember: C = Q/V)

Difference between isolated and circuit capicators:

• Isolated: voltage decreases, resulting in an increase in capacitance.
• Circuit: voltage is constant because it’s a circuit, but charge increases, resulting in increase capacitance.