electrical circuits 4.3

Question 1

potential divider equation

Answer 1

V(out) = V(in)(r/R+r)

Question 2

sensing circuit

Answer 2

resistance of the varying resistor decreases
potential difference over that part of the circuit decreases

Question 3

derivation of resistors in series

Answer 3

Ɛ=V+V+V+…
V=IR =>IR_t = IR+IR+…
R_t = R+R+R+…

Question 3

derivation of resistors in parallel

Answer 3

I_t = I+I+I+… (KCHF 1st law)
V/R=I - V is the same everywhere
V/(R_t)=V/R+V/R+…
1/(R_t)=1/R+1/R+…

Question 3

Internal resistance

Answer 3

resistance of an EMF source due to its construction (materials/chemicals)

Question 4

terminal pd

Answer 4

P.D. measured from external terminals of a cell
Ɛ = V(t) + V(l)

Question 4

what happens to V(t) under high current

Answer 4

Ɛ = V(t) + V(l)
Ɛ-Ir= V(t)
Ɛ - bigger => V(t) decreases

Question 4

when is Ɛ = V(t)

Answer 4

when there is no current
Ir -> 0

Question 4

derive equation relating {Ɛ, I, r}

Answer 4

V(t) = Ɛ - V(L)
R = component resistance
IR = Ɛ - Ir
Ɛ = I(R+r)

Question 4

Thermistor//LED

Answer 4

Low temperatures/LI, higher sensitivity
looks like 1/x graph (Temp/Res)
I = f(V) looks like v^3 - therm

Question 5

Potentiometer
(Very compact)
(linear/logarithmic)

Answer 5

variable res in low pd circuits (au lieu de P div)
3 terminals and sliding contact

Question 6

alternate Potential divider equation

Answer 6

R2 = R1((V_out)/(V_in-V_out))