ARCH-P-02: Electrical Power Dissipation (P = IV = I^2R = V^2/R), Grid Efficiency & Energy (E = VIt)

Full 15-Q Timed Drill

Step 1 of 6 • The Core Idea

ARCH-P-02: Why the 140s Classroom Method Fails Under the 90s Clock

Standard Classroom Method (Too Slow)~140s (Blows 90s Clock)

First compute total energy input

E_{\text{in}} = P t = 200 \times (5 \times 60) = 60000\text{ J}

. Next compute useful output

E_{\text{useful}} = 15\% \times 60000 = 9000\text{ J}

. Subtracting gives

E_{\text{wasted}} = 60000 - 9000 = 51000\text{ J}

(~120s).

The Fast ShortcutTarget: 40s (Saves 100s)

Line 1 (Wasted Power):

P_{\text{waste}} = (1 - 0.15) \times 200 = 170\text{ W}

.
**Line 2 (Multiply by

60t

):**

E_{\text{waste}} = 170 \times (5\times 60) = 51000\text{ J}

(25s).

Where Students Lose Time: In 11 past UAT-UK questions (4.72% of Physics), candidates lose 100s by substituting supply terminal voltage v_supply instead of cable voltage drop δv into v²/r. Instead, apply P1 with Maths 1 skill M1.2.

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