Suggested practical

Investigate the brightness of bulbs in series and parallel

This experiment will investigate how the brightness of bulbs changes depending on whether they are arranged in series or parallel.

Aim of the experiment

To see how the brightness of bulbs change as they are connected in series and parallel, and to measure the potential difference across the bulbs and the current through the bulbs in series and parallel.

Method

  1. Build a simple series circuit with one bulb and a battery. Add an ammeter in the loop and a voltmeter in parallel with the bulb, as shown in the first diagram.
  2. Take notes about the brightness of the bulb, for example whether it is bright or dim. Record the readings from the ammeter in amps (A) and the voltmeter in volts (V).
  3. Add another bulb into the loop, as shown in the second diagram. Record the bulb's brightness, current and potential difference.

Circuit containg a cell, ammeter and a lamp with a voltmeter in parallel.
This is a circuit showing two bulbs connected to a voltmeter each. There is one ammeter and one cell on the top row.

Repeat this method for each of the following circuits:

Description

Diagram

Circuit 3. Ammeter on each branch, voltmeter across each bulb

A circuit with two lamps in parallel to each other and both connected to a voltmeter each. There is an ammeter on both of the lamp’s rows.

Circuit 4. Ammeter on each branch, voltmeter across each bulb

A circuit with three lamps on three rows which are each connected to a voltmeter. There are three ammeters also on each row.

Circuit 5. Ammeter next to each bulb, voltmeter across each bulb

A circuit with three lamps and three voltmeters connected to the lamps, and two ammeters at the end of both rows.

Circuit 6. Ammeter next to each bulb, voltmeter across each bulb

A circuit with four lamps, four voltmeters, and two ammeters all in parallel across two rows.

Results

A suitable results table for each circuit might be:

BulbBrightnessCurrent (A)Potential difference (V)
1
2
3
4

These are example results for Circuit 5 (parallel circuit, two bulbs on one branch, single bulb on the other branch).

BulbBrightnessCurrent (A)Potential difference (V)
1Dim0.403.00
2Dim0.403.00
3Bright as single series bulb0.806.00

Analysis

  • Describe what you notice about the brightness of the bulbs in series and in parallel
  • Explain why some bulbs are brighter than others
  • Explain what the current and potential difference readings tell you about series and parallel circuits

Evaluation

When in series, bulbs become dimmer as the potential difference is shared equally across the bulbs. The current reads the same for each component.

In parallel, each branch shows the same potential difference, so the bulbs on one branch will have the same relative brightness. The current for each bulb will add up to the current near the battery.

Hazards and control measures

HazardConsequenceControl measures
Overheating components - hot bulbBurned fingers, scorched desk Use a heatproof mat. Switch off between readings to ensure components don't get too hot.
Blown bulbShattered glassNever exceed the maximum supply voltage.
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