Chapter 8 of 8

All 8 chapters
  1. 1What magnets pull, readunderstood
  2. 2North and south poles, readunderstood
  3. 3Magnetic force through things, readunderstood
  4. 4Making a compass, readunderstood
  5. 5Electricity: safe and unsafe, readunderstood
  6. 6A simple circuit, readunderstood
  7. 7Conductors, insulators and switches, readunderstood
  8. 8Circuit drawings, readunderstood

S2.8.8 Chapter 8

Circuit drawings

How can I draw a circuit so anyone can read it?

Your guess

Pick one before you read on. It is fine to be wrong.

Your guess

  • You picked A. Read on. At the end, the chapter comes back to your guess.

  • You picked B. Read on. At the end, the chapter comes back to your guess.

  • You picked C. Read on. At the end, the chapter comes back to your guess.

By the end you can

  • Draw a circuit using symbols for a cell, bulb, wire and switch
  • Predict from a drawing whether a bulb will light

Drawing a real cell and bulb takes time. So people draw circuits with short marks. Each mark is called a symbol.

Draw it first

Draw the four circuit symbols

  1. Four circuit symbols in a row. The first is a long line and a short thick line, labelled cell. The second is a circle with a cross inside, labelled bulb. The third is a lever between two dots, lifted up, labelled switch. The fourth is one straight line, labelled wire.cell

    1 Draw a long line and a short thick line. Write cell.

  2. Four circuit symbols in a row. The first is a long line and a short thick line, labelled cell. The second is a circle with a cross inside, labelled bulb. The third is a lever between two dots, lifted up, labelled switch. The fourth is one straight line, labelled wire.cellbulb

    2 Draw a circle with a cross inside. Write bulb.

  3. Four circuit symbols in a row. The first is a long line and a short thick line, labelled cell. The second is a circle with a cross inside, labelled bulb. The third is a lever between two dots, lifted up, labelled switch. The fourth is one straight line, labelled wire.cellbulbswitch

    3 Draw two dots with a lifted lever. Write switch.

  4. Four circuit symbols in a row. The first is a long line and a short thick line, labelled cell. The second is a circle with a cross inside, labelled bulb. The third is a lever between two dots, lifted up, labelled switch. The fourth is one straight line, labelled wire.cellbulbswitchwire

    4 Draw one straight line. Write wire.

A switch can be open or closed. An open switch has its lever lifted. A closed switch has its lever lying flat.

Two switch symbols side by side. The first has its lever lifted between two dots, labelled switch open. The second has its lever lying flat between two dots, labelled switch closed. Labels: switch open, switch closed.switch openswitch closed
An open switch leaves a gap. A closed switch has no gap.

One cell is one long line and one short line. The long line is the plus end, +. On a real cell, that is the knob end. In drawings we say cell, not battery. Two or more cells joined make a battery.

A drawing of a whole circuit is a circuit diagram. Wires are straight lines with square corners.

See it three ways

As a picture

A circuit diagram. A cell, labelled cell, and a bulb, labelled bulb, are joined by wires along the top. A closed switch, labelled switch, is on the bottom wire. The wires make a complete loop.cellbulbswitch

In words

The switch is closed. The wires make a complete loop with a cell in it. The bulb lights.

You can tell if a bulb will light. Trace the loop with your finger. Start at one end of the cell.

Follow the wire round. If you meet an open switch, stop. There is a gap. The bulb stays dark.

If you get back to the start, the loop is complete. Check there is a cell. Then the bulb lights.

A circuit diagram. A cell, labelled cell, and a bulb, labelled bulb, are joined by wires along the top. An open switch, labelled switch, is on the bottom wire. Its lever is lifted, so there is a gap.cellbulbswitch
The switch is open. There is a gap. The bulb stays dark.

A circuit with no cell stays dark too. Nothing pushes the electricity round.

Try it

Draw a circuit and predict

You need: paper and a pencil, a ruler or a straight edge, if you have one, if you can, your cell, bulb, foil and paper clip.

Be safe: Use only a torch cell. Never let the foil from the two cell ends touch. It gets hot fast.

  1. Draw a cell, a bulb and a switch in a loop. Use symbols.
  2. Draw the switch closed. Trace the loop with your finger.
  3. Will the bulb light? Write yes or no.
  4. Draw it again with the switch open. Write yes or no.
  5. If you can, build both. Use a paper clip as the switch. Check your answers.

What you will see: With the switch closed, the loop is complete. The bulb lights. With the switch open, there is a gap. The bulb stays dark. A drawing can predict what the real circuit does. No parts? The drawings are the whole activity.

If you cannot try it, this is what happens.
Two circuit drawings, one above the other. The top drawing has a cell, a bulb and a closed switch. Under it are the words bulb lights. The bottom drawing has a cell, a bulb and an open switch. Under it are the words bulb dark.bulb lightsbulb dark
Two circuit diagrams, one above the other. Each has a cell, a bulb and an open switch. In the top one the switch comes before the bulb, labelled switch before the bulb. In the bottom one the switch comes after the bulb, labelled switch after the bulb.switch before the bulbswitch after the bulb
The switch is open in both. In both, the bulb stays dark.

A wrong idea many people have

A switch only stops the bulb if it comes before the bulb.

Why it feels right: Electricity leaves the cell and meets the switch first. It seems to stop only what comes next.

The test that breaks it: Look at the two drawings. Open the switch in each. Trace each loop with your finger. Both have a gap. Or build it. Move the paper clip switch to the other side of the bulb. The bulb is dark both times.

What is true: All the parts are in one loop. A gap anywhere stops the whole loop.

Key words

symbol
a short mark that stands for a part, such as a cell.
circuit diagram
a drawing of a circuit made with symbols.

Back to your guess

The answer is A: Use a short mark for each part.

People use symbols. These are short marks for each part. Anyone can read them.

Check yourself

Try each one before you look. A wrong answer tells you where to go next.

  1. Look at the picture. Which one is a cell?

    Three symbols in a row, labelled A, B and C. A is a circle with a cross inside. B is a long line and a short thick line. C is a lifted lever between two dots. Labels: A, B, C.ABC
    Tap your answer.

    1. Not this one. A circle with a cross is a bulb. Try another.

    2. Yes, that is right. One cell is a long line and a short thick line.

    3. Not this one. A lever between two dots is a switch. Try another.

    See the answer

    B

    One cell is a long line and a short thick line.

    • If you chose A: A circle with a cross is a bulb.
    • If you chose C: A lever between two dots is a switch.

  2. Look at the drawing. Will the bulb light?

    A circuit diagram with a cell, labelled cell, a bulb, labelled bulb, and an open switch, labelled switch. The lever of the switch is lifted.cellbulbswitch
    Tap your answer.

    1. Not this one. A cell and a bulb are not enough. The loop must be complete. Go to S2.8.6. Try another.

    2. Not this one. The open switch is a gap. A gap stops the whole loop. Go to S2.8.6. Try another.

    3. Yes, that is right. An open switch breaks the loop. Nothing goes round, so the bulb stays dark.

    See the answer

    No. The open switch leaves a gap.

    An open switch breaks the loop. Nothing goes round, so the bulb stays dark.

    • If you chose A: A cell and a bulb are not enough. The loop must be complete. Go to S2.8.6.
    • If you chose B: The open switch is a gap. A gap stops the whole loop. Go to S2.8.6.

  3. Look at the drawing. Will the bulb light?

    A circuit diagram with a cell, labelled cell, a bulb, labelled bulb, and a closed switch, labelled switch. The lever of the switch lies flat.cellbulbswitch
    Tap your answer.

    1. Not this one. Only an open switch stops a bulb. A closed switch joins the loop. Try another.

    2. Not this one. A cell is the part that pushes. This drawing has one. Try another.

    3. Not this one. One cell can light a bulb. The loop is complete, so it lights. Try another.

    4. Yes, that is right. The switch is closed and there is a cell. So the loop is complete and the bulb lights.

    See the answer

    Yes. The loop is complete.

    The switch is closed and there is a cell. So the loop is complete and the bulb lights.

    • If you chose A: Only an open switch stops a bulb. A closed switch joins the loop.
    • If you chose B: A cell is the part that pushes. This drawing has one.
    • If you chose C: One cell can light a bulb. The loop is complete, so it lights.

  4. A drawing has a bulb and a closed switch, but no cell. Will the bulb light?

    Tap your answer.

    1. Not this one. A closed switch is not enough. A loop needs a cell to push. Go to S2.8.6. Try another.

    2. Yes, that is right. A cell pushes the electricity round the loop. Without one, the bulb stays dark.

    3. Not this one. A loop with no cell has nothing to push. The bulb stays dark. Go to S2.8.6. Try another.

    See the answer

    No. Nothing pushes the electricity round.

    A cell pushes the electricity round the loop. Without one, the bulb stays dark.

    • If you chose A: A closed switch is not enough. A loop needs a cell to push. Go to S2.8.6.
    • If you chose C: A loop with no cell has nothing to push. The bulb stays dark. Go to S2.8.6.

  5. Draw a circuit with a cell, a bulb and a closed switch. Will the bulb light?

    See the answer

    A loop. A long and a short line for the cell. A circle with a cross for the bulb. A lever touching both dots. Yes, the bulb lights.

    The loop is complete and has a cell. So the bulb lights.

  6. From an earlier chapter

    Which would light the bulb if laid across a tester gap?

    Tap your answer.

    1. Not this one. Wood is an insulator. It leaves the gap. Go to S2.8.7. Try another.

    2. Not this one. Plastic is an insulator. It leaves the gap. Go to S2.8.7. Try another.

    3. Yes, that is right. A paper clip is a metal. Metals are conductors, so the loop is complete.

    See the answer

    A metal paper clip

    A paper clip is a metal. Metals are conductors, so the loop is complete.

    • If you chose A: Wood is an insulator. It leaves the gap. Go to S2.8.7.
    • If you chose B: Plastic is an insulator. It leaves the gap. Go to S2.8.7.

  7. Look at the picture. Which one is a closed switch?

    Three symbols in a row, labelled A, B and C. A is a lever lying flat between two dots. B is a lever lifted up between two dots. C is a long line and a short thick line. Labels: A, B, C.ABC
    Tap your answer.

    1. Yes, that is right. A closed switch has its lever lying flat on both dots. There is no gap.

    2. Not this one. In B the lever is lifted. A lifted lever leaves a gap, so B is an open switch. Try another.

    3. Not this one. C is a cell. Its mark is a long line and a short thick line. Try another.

    See the answer

    A

    A closed switch has its lever lying flat on both dots. There is no gap.

    • If you chose B: In B the lever is lifted. A lifted lever leaves a gap, so B is an open switch.
    • If you chose C: C is a cell. Its mark is a long line and a short thick line.

  8. Look at the drawing. It has two switches. Will the bulb light?

    A circuit diagram with a cell, a bulb and two switches. One switch has its lever lying flat. The other has its lever lifted. Labels: cell, bulb, switch, switch.cellbulbswitchswitch
    Tap your answer.

    1. Not this one. Both switches are in the one loop. The open one is a gap, so the whole loop stops. Try another.

    2. Yes, that is right. Every part is in one loop. A gap stops the bulb, even with a closed switch beside it.

    3. Not this one. A cell is needed, but it is not enough. The open switch leaves a gap. Try another.

    See the answer

    No. One open switch leaves a gap.

    Every part is in one loop. A gap stops the bulb, even with a closed switch beside it.

    • If you chose A: Both switches are in the one loop. The open one is a gap, so the whole loop stops.
    • If you chose C: A cell is needed, but it is not enough. The open switch leaves a gap.

  9. Why do people draw circuits with symbols?

    Tap your answer.

    1. Not this one. Symbols do not show looks. They show which part it is and how the parts join. Try another.

    2. Not this one. Real parts can be drawn. A symbol is just faster, and anyone can read it. Try another.

    3. Yes, that is right. A short mark for each part saves time. People who share the same marks can all read the drawing.

    4. Not this one. Anyone can learn the symbols. That is why they are used. Try another.

    See the answer

    Symbols are quick to draw and anyone can read them.

    A short mark for each part saves time. People who share the same marks can all read the drawing.

    • If you chose A: Symbols do not show looks. They show which part it is and how the parts join.
    • If you chose B: Real parts can be drawn. A symbol is just faster, and anyone can read it.
    • If you chose D: Anyone can learn the symbols. That is why they are used.

  10. A circuit has an open switch before the bulb. Ravi moves it to the other side of the bulb. What happens?

    Tap your answer.

    1. Not this one. All the parts are in one loop. A gap anywhere stops the whole loop. Try another.

    2. Not this one. A gap stops the electricity completely. The bulb is fully dark. Try another.

    3. Not this one. Moving a switch does not close it. It is still open, so the gap stays. Try another.

    4. Yes, that is right. The cell, switch and bulb are in one loop. An open switch is a gap, wherever it sits.

    See the answer

    The bulb stays dark, wherever the open switch is.

    The cell, switch and bulb are in one loop. An open switch is a gap, wherever it sits.

    • If you chose A: All the parts are in one loop. A gap anywhere stops the whole loop.
    • If you chose B: A gap stops the electricity completely. The bulb is fully dark.
    • If you chose C: Moving a switch does not close it. It is still open, so the gap stays.

Keep it

Copy this into your exercise book.

A cell is a long line and a short line. A bulb is a circle with a cross. A switch has a lever. A bulb lights only in a complete loop. A gap or an open switch stops it.

Draw: A loop with a cell, a bulb and a switch, as symbols.

Reading with a child? A short page for the adult: what this chapter teaches and three questions to ask.

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