Websink Prep UKKS2 ScienceYear 6 chaptersScience textbooksYear 1Year 2Year 3Year 4Year 5Year 6Year 7Year 8Year 9Browse allPast papersFind a tutorBecome a tutor
Primary Science · Year 6Chapter 10 · Components, switches and circuit symbols
Year 6 Science · Components, switches and circuit symbols · Lesson 10.3

Year 6 Science: More bulbs in a loop

Part of the Year 6 Science components, switches and circuit symbols chapter. Chapter overview · whole chapter on one page

10.3

More bulbs in a loop

Year 6
EL2: compare and give reasons for variations in how components function, including the brightness of bulbs
Story. Mo adds a second bulb to his loop, joined in a row with the first. “Both bulbs look dimmer,” he says. “Why?” Mrs Chen says, “The same voltage now has to share between two bulbs. Each bulb gets less of it, so each one is dimmer.”

Bulbs can be joined one after another in a row, in the same loop. This is called joining them in series.

When two bulbs are in a row with one cell, the voltage is shared between them. Each bulb gets less current, so each one is dimmer than a single bulb with the same cell.

one cell, one bulb
A loop with one cell and one bulb.
one cell, two bulbs in a row
A loop with one cell and two bulbs in a row.

The table compares the brightness of the bulbs, rated out of 5, with two cells.

CircuitBrightness rating (out of 5)
2 cells, one bulb4
2 cells, two bulbs in a row (each bulb)2
012345brightness rating (out of 5)4one bulb2each of two bulbs
Bar chart: one bulb is rated 4 out of 5, and each bulb in a row of two is rated 2 out of 5.

Key ideas

  • Bulbs in a row in one loop share the voltage between them.
  • Each bulb in a row gets less current, so each one is dimmer.
  • One bulb on its own in the same loop is brighter.
  • Adding a bulb to a loop changes how bright all the bulbs in the loop are.
Worked example 10.3.1
Look at the table in section 10.3. How bright is one bulb on its own, with two cells? Write the rating out of 5.

Method. Read the table.

  1. Read the row. One bulb with two cells is rated 4 out of 5.
    4
  2. Write the rating. So the rating is 4 out of 5.
    4 out of 5
  3. Write the answer.
    4 out of 5

Check. The single bulb is brighter. ✓

Worked example 10.3.2
How much dimmer is each bulb in a row of two, compared with one bulb? Write the number of rating points.

Method. Subtract the two-bulb rating from the one-bulb rating.

  1. Read the ratings. One bulb is rated 4, and each of two bulbs is rated 2.
    4 and 2
  2. Subtract. The difference is 4 minus 2.
    4 - 2 = 2
  3. Write the answer.
    2 points

Check. 2 + 2 = 4. ✓

Worked example 10.3.3
Why is each bulb in a row dimmer than a single bulb? Write the reason in one sentence.

Method. Think about the voltage.

  1. Think about the voltage. The voltage is shared between the two bulbs.
    shared
  2. Think about the current. So each bulb gets less current, which makes it dimmer.
    less current
  3. Write the answer.
    the voltage is shared, so each bulb gets less current

Check. Sharing the voltage makes each bulb dimmer. ✓

Watch out

Watch out: two bulbs in a row do not each get the full voltage. The voltage is shared, so each bulb is dimmer than a single bulb.

Exam tip

Exam tip. When you explain a bulb being dimmer, say that the voltage is shared, so less current flows through each bulb.

Try it (with your teacher, or a grown-up at home). With a teacher, make a loop with one cell and one bulb. Note the brightness. Then add a second bulb in a row, and compare the brightness of both bulbs. Discuss why the bulbs are dimmer. Use ratings out of 5, and keep the cell the same.

Exercise 10C  More bulbs in a loop

1
FWhat is the brightness rating of one bulb with two cells? Write the number out of 5.
2
FWhat is the brightness rating of each bulb when two bulbs are in a row? Write the number out of 5.
3
FHow many more rating points is one bulb than each of two bulbs in a row? Write the number.
4
FAre the bulbs in a row dimmer than one bulb on its own? Write yes or no.
5
FWhich circuit has the brighter bulb: one bulb with two cells, or two bulbs in a row with two cells? Write one bulb or two bulbs in a row.
6
FIs the voltage shared between the bulbs in a row? Write yes or no.
7
FWhat do we call bulbs joined one after another in the same loop? Write the words.
8
PSA loop has one cell and one bulb rated 4. A second bulb is added in a row, and both are rated 2. How many points dimmer is each bulb? Write the number.
9
PSRuby says that adding a second bulb in a row makes the first bulb brighter. Is Ruby right? Write yes or no.
10
PSAli adds a bulb to a loop and says the bulbs are now the same brightness as one bulb. Is Ali right? Write yes or no.
11
RExplain why a bulb in a row of two is dimmer than a bulb on its own, in terms of the current. Write one sentence.
12
RExplain why the bulbs in a row are not as bright as a single bulb, even with the same cell. Write one sentence.
13
RChallenge: explain how you could make the two bulbs as bright as one bulb, by changing the cells. Write one sentence.

Websink Prep UK is an independent site. It is not affiliated with, endorsed by or sponsored by AQA, Pearson Edexcel, OCR, WJEC, Eduqas, CCEA, SQA, GL Assessment, CEM or the Department for Education. All exam board names and trademarks belong to their owners. Past papers are linked from the exam boards' own websites and are not hosted here.

About Websink Prep UK · Find a tutor · Privacy · Terms · Cookie settings