Chapter Boss: Circuit Master

Why it matters

Six lessons, one boss. Charge, cells, Ohm, wires, circuits, bills — everything on the table at once.

The idea in plain words

The chapter in one breath. Tap each law.

V = I·R · P = V·I · E = P·t

An electric iron is rated 1100 W, 220 V. Find its current and resistance.

I = 5 A, R = 44 Ω

• the circuit law: V = I·R — Ohm's law — voltage drives current against resistance
• watt (W): P = V·I — power — how fast electrical energy is converted
• kWh: E = P·t — energy — what the meter counts and the bill charges
• I = P ÷ V = 1100 ÷ 220 = 5 A
• R = V ÷ I = 220 ÷ 5

Predict first

A 6 V battery drives 4 Ω and 8 Ω connected in PARALLEL. The total current from the battery is…

Parallel: Rp = 8/3 ≈ 2.67 Ω, smaller than either branch — so I = 6 ÷ 2.67 = 2.25 A.

• 2.25 A — correct
• 0.5 A
• 6 A

What you do

Boss circuit: a 2 Ω guard in the main line, then 3 Ω and 6 Ω in parallel, all on 12 V. Collapse it step by step — the meters are hidden until you call them right.

Check yourself

In a series circuit the current after the last bulb, compared to before the first, is…

Charge is conserved: the same current threads the whole loop. Bulbs convert ENERGY, never charge.

120 C of charge passes in one minute. The current is…

I = Q ÷ t = 120 ÷ 60 = 2 A.

Under a heavy load, a battery's terminal voltage…

V = ε − I·r: the bigger the current, the more volts die inside the cell.

A filament bulb is non-ohmic because…

The V–I curve bends because the glowing filament's temperature — and hence R — keeps climbing.

Double a wire's area of cross-section. Its resistance…

R = ρl/A — area sits in the denominator. Wider road, easier traffic.

A 500 W TV runs 4 h daily. At ₹8 per unit, the month costs…

0.5 kW × 4 h = 2 kWh/day → 60 kWh/month → 60 × ₹8 = ₹480.

• the same — correct
• smaller — bulbs consume current
• larger
• 2 A — correct
• 120 A
• 0.5 A
• drops below its e.m.f. by I·r — correct
• equals its e.m.f. exactly
• rises above its e.m.f.
• its resistance rises as the filament heats — correct
• it converts current into light
• glass blocks electrons
• halves — correct
• doubles
• quadruples
• ₹480 — correct
• ₹16,000
• ₹48