Series & Parallel Circuits — A/L Physics

What must I remember about Series & Parallel Circuits?

• Series Resistor Combination: Same current I passes sequentially through each resistor: Equivalent Resistance R_eq = R1 + R2 + R3; Total voltage V_total = V1 + V2 + V3; Voltage Divider Rule: V1 = V * [R1 / (R1 + R2)].
• Parallel Resistor Combination: Same potential difference V across each parallel branch: 1 / R_eq = 1/R1 + 1/R2 + 1/R3; For two resistors: R_eq = (R1 R2) / (R1 + R2); Current Divider Rule: I1 = I * [R2 / (R1 + R2)].
• Grouping of Identical Cells: N cells in Series: E_eq = N E, r_eq = N r; M cells in Parallel: E_eq = E, r_eq = r / M; Mixed combination of m parallel rows of n series cells: E_eq = n E, r_eq = (n r) / m.
• Electrical Power & Heating (Joule's Law): Power dissipated in resistor: P = V * I = I² R = V² / R; Heat energy generated Q = I² R t.

Test yourself (1 minute)

1. Ammeter & Voltmeter Design

   Moving Coil Galvanometer (resistance G, full-scale deflection current Ig): Converted to Ammeter by connecting low-resistance Shunt S in PARALLEL: S = (Ig G) / (I - Ig); Converted to Voltmeter by connecting high-resistance Multiplier R in SERIES: R = (V / Ig) - G.

2. Ideal Meter Characteristics

   Ideal Ammeter has ZERO resistance (zero circuit disturbance); Ideal Voltmeter has INFINITE resistance (draws zero current).

3. Equivalent resistance bounding rules

   Series R_eq is always GREATER than the largest individual resistor; Parallel R_eq is always SMALLER than the smallest individual resistor.

Practise Series & Parallel Circuits questions today

Source: NIE G.C.E. (A/L) Physics Resource Book - Unit 7: Current Electricity

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Where does Series & Parallel Circuits fit in the syllabus?

Unit 7.4 · Year 2 · Term 1