10 - Electrical circuits

Question 1

What is Kirchoff’s second law?

Answer 1

In any circuit, the sum of electromotive forces is equal to the sum of potential differences around a closed loop.

Σε= Σv

Question 2

How can you calculate the total resistors for resistors connected in series?

Answer 2

Rₜ = R₁ + R₂ + R₃

Question 3

How can you calculate the total resistors for resistors connected in parallel?

Answer 3

1/Rₜ = 1/R₁ + 1/R₂ + 1/R₃

Question 4

What are the 4 key electrical relationships for complex circuit problems?

Answer 4

I = ΔQ/Δt
current = charge flow/time

V = W/Q
voltage = work done / charge

P = VI
power = voltage x current

V = IR
voltage = current x resistance

Question 5

What are the two main formulas involving internal resistance?

Answer 5

r = V/I
internal resistance = voltage/current

ε - Vₗ = r
e.m.f - lost volts = internal resistance

Question 6

What is a potential divider?

Answer 6

A potential divider is a simple circuit that uses resistors to supply a variable output or potential difference.

Vₒᵤₜ = (R₂ / R₁ + R₂)*Vᵢₙ

Question 7

What is loading (potential dividers)?

Answer 7

Loading refers to connecting a component to Vₒᵤₜ (placing a component in parallel with R₂). THis lowers the resistance of this part of the circuit, lowering Vₒᵤₜ.

If the load has a small resistance, Vₒᵤₜ is significantly reduced.
(1/Rₜ = 1/R₁ + 1/R₂ + 1/R₃)

Question 8

What is a potentiometer?

Answer 8

A potentiometer works in the same way as a potential divider, however instead of using two resistors in series it uses a length of resistance wire with a sliding contact.

When the contact is moved towards A,