EE-202
Copy Right ©️ ：Farah Vandrevala
EE202LRA1:Circuit Analysis:220910582

Basic Components and Circuit Variables

Circuit Terminology

  1. Electric: Mathematical model that approximates the behavior of a actual electical system.

  2. Electric Charge(Q): Charge conservation gener governs the working of electrival circuits. Charge(Q),measured in Coulum (C)

  3. Current(I): Rate of flow of change. measured in Ampere(A).
    i = dQ / dt = Q / t
    1A = 1C / 1S

  4. Voltage(V) (Potential difference): Force that causes current to flow from higher potential point to lower potential point.
    Vab = Va - Vb
    Amount of work done (energy expended) to move charge is voltage.
    V = dW / dQ = W / Q

  5. Power(P): Rate at which energy is expended. measured in Watts(W).
    Voltage & Current are mesureable variables.
    P = dW / dt = W / t = dW / dq X dq / dt
    P = V * I
    1W = 1V * 1A

  6. Energy(W): the cost of … , measured in Joules(J).
    W = V * Q

Example

P1

If 5A of constant current passes through a conductor, how many electrons pass through a given point in 1 minute?

Given:

  • i = 5A
  • t = 1min

Find:

  • number of e, e = -1.6 * 10^19 C

Know:

  • Amount of charge on each electron

i = q / t
q = i * t = 5A * 60s = 300C

Verify:

  • Balance the units

e- = q / |e-| = 1.875 * 10^21 electrons = 300C / 1.6 * 10^19 C

P2

In a circuit, 9.25 uJ of energy is needed to move 0.5 uC of charge from point A to point B. What is the voltage between the points?

Given:

  • W = 9.25 uJ
  • q = 0.5 uC

Find:

  • Vab = W / Q = 9.25 * 10^-6 J / 0.5 * 10^-6 C = 18.5 V

Verify:

  • Balance units 1V = 1J / 1C

P3

A 120V battery is connected across a 100W bulb. How many electrons pass through the bulb in 1 hour?

Given:

  • V = 120V
  • P = 100W
  • t = 1h

Find:

  • number of e
    • Need: Total charge
      • Current

Know:

  • P = V * I
  • I = P / V = 100W / 120V = 5/6A
  • I = Q / t = I * t = 5/6 * 60s * 60min = 3000C
  • #of e- = Q / |e-| = 3000C / 1.6 * 10^-19C = 1.875 * 10^22 e

P4

A smartphone has a 3.8V battery whose charge capacity is 1.5mAh. One full cycle of charge will last 12h on talk time, and 10days on stanby. How mauch power is consumed in each case?

q = i * t
1C = 1A * 1S = 1A * 3600s = 1Ah

Given:

  • V = 3.8V
  • Q = 1.5mAh
  • Talk time mode: t = 12h

Find:

  • P

Know:

  • W = V * Q
  • P = W / t
  • P = (V * Q) / t = [3.8V * (1.5 * 10^-3Ah)] / 12h = 475 * 10^-6W = 475 mW