50 lamps, each of resistance 8.0 Ω8.0\ \Omega8.0 Ω, are connected in series to a 200 V200\text{ V}200 V supply in order to decorate a tree.
Calculate:
(i) the current in each lamp,
(ii) the power dissipated in each lamp.
The lamps are designed to "fail-short". If a filament fails, the lamp shorts so that it has no resistance. The other lamps continue to light and the current increases.
The lamps are connected through a fuse that blows when the current rises above 0.65 A0.65\text{ A}0.65 A. At this current, the resistance of each lamp is 10%10\%10% greater than its normal working resistance.
Calculate the maximum number of lamps that can fail before the fuse blows.
136 exam-style questions on CIE IGCSE Physics 4.3 Electric circuits, covering 4.3.1a Circuit diagrams and circuit components, 4.3.2a Series circuits, 4.3.2b Parallel circuits, 4.3.2c Current and potential difference in circuits, 4.3.2d Combined resistance of resistors in parallel, and 4.3.3 Action and use of circuit components. Each one has a worked solution and a mark scheme showing where the marks go.