Analysing Circuits

Question 1

Equation for current

Answer 1

I = delta Q divided by delta t

Question 2

Equations for potential difference

Answer 2

V = W/Q (potential difference = work done divided by charge)
V = IR (potential difference = current*resistance)

Question 3

Equations for power

Answer 3

P = VI
P = I^2R
P = V^2/R

Question 4

When analysing a complex circuit, what do you need to keep in mind that will help with the question?

Answer 4

• Kirchhoff’s 1st law (current in a junction = current out of a junction)
• Kirchhoff’s 2nd law (for every closed loop within a circuit, electromotive force = potential difference)
  I = delta Q / delta t (Current = change in charge divided by change in time)
  V = W / Q (Potential difference = work done divided by charge)
  P = VI (Power = potential difference times current)
  Most importantly: V = IR (potential difference = current*resistance)

Question 5

Kirchhoff’s First Law

Answer 5

In any closed system, the total charge in the system is conserved. Conservation of charge states that electric charge can neither be created nor destroyed. The total amount of charge in the universe is constant.

At any junction in a circuit, the total current leaving the junction is equal to the total current entering the junction.

Question 6

Kirchhoff’s Second Law

Answer 6

In any circuit, the sum of the electromotive forces is equal to the sum of the potential differences around a closed loop. (AKA: Kirchhoff’s Voltage Law)

Question 7

What is the purpose of a potential divider?

Answer 7

To provide variable potential difference, or to provide a constant specific potential difference

Question 8

What equation can be used to calculate the voltage out of a potential divider in terms of input voltage and resistances in the circuit?

Answer 8

Vout = (Rout/Rtotal) * Vin

Question 9

Voltage drops

Answer 9

Literally just the potential difference supplied to the components in a working circuit