Year 9 Science · Unit 3 · Lesson 18
Apply Worksheet
Learning Goals
1. A car’s two headlights are wired in parallel. What happens to the second headlight when one bulb blows, and why?
Cause and effect: adding a lamp in series
Complete the chain. Each box is caused by the one before it.
2. The same three lamps are now connected in parallel to the same battery instead. Predict how brightly each lamp glows, compared with one lamp connected on its own, and explain why.
Real-world context: wiring a rooftop solar array
A house has 16 solar panels. In full sunshine, each panel produces 40 V and a current of 10 A. The installer wires the panels in two strings: in each string, 8 panels are connected in series. The two strings are then connected in parallel to the inverter, which changes the electricity into the kind used in the house.
Source: sample values for this worksheet.
3. Calculate (a) the voltage of one string, (b) the current from one string, (c) the total current from the two strings together, and (d) the total power of the array, using P = V × I.
(a) One string V
(b) One string A
(c) Both strings A
(d) Array power W
Investigation: adding lamps in parallel
Kai’s group modelled the lighting in a house: identical lamps side by side on a 6.0 V power pack, switching on one more lamp each time. They recorded the current from the power pack.
| Lamps switched on | Current from the power pack (A) | Total resistance (Ω) |
|---|---|---|
| 1 | 0.50 | 12 |
| 2 | 1.00 | |
| 3 | 1.50 | |
| 4 | 2.00 |
Source: sample class results.
4. Graph the results in Table 1, with the number of lamps on the horizontal axis.
5. Use R = V ÷ I to complete the last column of Table 1. Describe the trend in that column, and explain it.
6. Explain why solar installers combine series and parallel wiring in one array. Describe what series wiring does for the array, what parallel wiring adds, and why two parallel strings cope better when a tree shades one panel than all 16 panels in one long series string would.