More batteries, brighter bulb

Science · Energy · ages 10-11

Name ______________________ Date ____________

A working buzzer gets louder after cells are added in series so their voltages add. The new total stays within its rating, and nothing else changes. Why does it get louder?
- They make the connecting wires much shorter
- They send more energy through the buzzer
- They make the open switch gap much wider
A working circuit has two cells and a dim bulb rated for three matching cells. You add a matching third cell in series so its voltage adds to theirs. What happens to the bulb?
- It gets brighter
- It gets dimmer
- It stays the same
Three matching cells power the same working bulb in series, connected so their voltages add. The bulb is rated for their total voltage. True or false: they provide less energy per unit charge than one of these cells.
Circle one: True False
Nadia's working circuit has two cells and a quiet buzzer. She wants it louder without adding a cell. She will keep any new total voltage within the buzzer's rating. What could she try?
- Replace both cells with two higher-voltage cells
- Keep the same cells and use a much longer wire around the case
- Keep the same cells and add another switch
Look at the bar chart showing bulb brightness for different numbers of cells. Which number of cells gives the brightest bulb?
- 1 cell
- 2 cells
- 3 cells
A circuit's brightness score equals the number of cells used, when all cells have the same voltage. With 2 cells the score is 2. What is the score with 4 cells?
Answer: ______________
A buzzer sounds quiet with one low-voltage cell. The buzzer is rated for a higher voltage. A friend swaps in one suitable higher-voltage cell. What is the best prediction?
- Same sound, because the circuit still has one cell in it
- It stops, because the higher voltage damages this small buzzer immediately
- It sounds louder, because higher voltage sends more energy through it
Theo says, 'A circuit with a broken wire and three cells will glow brighter than a circuit with one cell and a complete wire.' What is wrong with his idea?
- Three cells force a wire to break before current can flow
- A broken circuit has no current, even with extra cells
- Broken wires stop buzzers but let bulbs keep glowing

Answer key

For grown-ups. Fold this page away before handing over the rest.

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They send more energy through the buzzer · In this test, the added cells raise the total voltage within the buzzer's rating. More electrical energy is transferred to the buzzer each second, making it louder.
It gets brighter · The matching third cell is connected so the voltages add. The new total is within the bulb's rating, so the larger voltage makes this bulb brighter.
False · The three matching cells have a larger total voltage because their voltages add. Voltage is energy transferred per unit charge, so they provide more energy per unit charge, not less. The statement is false.
Replace both cells with two higher-voltage cells · Suitable higher-voltage replacements can raise the total voltage without changing the number of cells. Nadia must keep that new total within the buzzer's rating.
3 cells · The bar labelled "3 cells" is tallest, so it has the greatest brightness score in this chart.
4 · The question defines the test score as the number of cells, so four cells give a score of 4.
It sounds louder, because higher voltage sends more energy through it · The number of cells stays at one, but the suitable cell has a higher voltage. That can transfer more energy per unit charge and make the buzzer louder.
A broken circuit has no current, even with extra cells · Cells only add energy to a circuit that is complete. A broken circuit has no current, so extra cells make no difference until it is fixed.