In a domestic circuit five LED bulbs are arranged as shown. The source voltage is 220 V and the power rating of each bulb is marked in the circuit diagram.
In a domestic circuit five LED bulbs are arranged as shown. The source voltage is 220 V and the power rating of each bulb is marked in the circuit diagram. Based on the following circuit diagram, answer the following questions :
Generated by claude-sonnet-4-6 · 2026-06-15 06:46 · grounding stimulus
Model Answer
(a)
(i) When K₁ is closed: Bulb A glows (top branch is complete).
(ii) When K₂ is closed: Bulbs B, C, D, and E glow (lower branch is complete).
(b) Each of bulbs B, C, D, E is rated 11 W, 55 V.
$$I_B = \frac{P}{V} = \frac{11}{55} = \textbf{0.2 A}$$
(c)
(i) Resistance of bulb B:
$$R_B = \frac{V^2}{P} = \frac{55 \times 55}{11} = \frac{3025}{11} = \textbf{275 Ω}$$
(ii) Since all four bulbs (B, C, D, E) are identical and connected in series (total voltage = 4 × 55 V = 220 V):
$$R_{total} = 4 \times 275 = \textbf{1100 Ω}$$
---
Explanation
- (a) Each key activates a separate branch — K₁ for bulb A alone, K₂ for the group of four bulbs.
- (b) Use $I = P/V$ with the rated values of bulb B (11 W, 55 V), not the source voltage.
- (c)(i) Use $R = V^2/P$ with bulb B's own rated voltage (55 V). (c)(ii) Four identical bulbs in series: $R_{total} = 4R_B$. The series arrangement is confirmed because 4 × 55 V = 220 V (source voltage), consistent with series connection sharing equal voltage.