The method and the results are on the series and parallel circuits lab. Do the analysis yourself first, then check the answers below.
Quick answer: In a series circuit the components are connected in one single loop, so there is only one path for the current and the bulbs share the supply. These answers go with the grade 7 science lab on series and parallel circuits: the graph, the calculations, the uncertainties and the conclusion explained, for all 8 analysis questions.
Model answers based on the sample data. Your own numbers will differ because bulbs and cells vary, but the pattern should be the same: strong dimming in series and almost no dimming in parallel. Also, use the sample percentages to check your method.
Level: Grade 7 science (Year 8 · Class 7) · Curriculum: MS-PS2-3
Question 1 Describe the pattern
In series the brightness of each bulb falls sharply as more bulbs are added (480, 45, 9 lux). In parallel it stays almost the same (480, 472, 466 lux). Series dims, parallel does not.Question 2 Series percentages
Two bulbs: 45 ÷ 480 × 100 = 9.4 %.Three bulbs: 9 ÷ 480 × 100 = 1.9 %.
Question 3 Parallel percentages
Two bulbs: 472 ÷ 480 × 100 = 98.3 %.Three bulbs: 466 ÷ 480 × 100 = 97.1 %.
Question 4 Explaining series
In series the same cells must push charge through every bulb, so the supply voltage is shared. Each bulb gets a smaller share of the energy, so it is dimmer. Energy is shared.Question 5 A small drop in parallel
In addition, the cells must supply more current for more bulbs, and real cells cannot keep their voltage perfectly under a bigger load. The voltage across each bulb is slightly lower.Question 6 Cell life
Series with three bulbs draws the smallest current, so the cells last longest. Moreover, a single bulb is in the middle. Three bulbs in parallel draw about three times the current, so the cells last about one third as long. Parallel drains cells fastest.Question 7 Reliability
Hold the light meter at exactly the same distance each time, use a shield tube and a dim room, and repeat readings to take a mean. Same distance, dim room, repeats.Question 8 Unscrewing a bulb
In series: all the other bulbs go out because the loop is broken.In parallel: the other bulbs stay lit with the same brightness.
