Experiment - Constructing electric circuits

In this experiment you will construct circuits by interpreting circuit diagams and then test the circuits by collecting the readings on the meters when the circuit is switched on.


To become familiar with interpreting circuit diagrams and reading electric meters. 


Apparatus (Equipment)

1 x DC variable power supply, with a nominal range from 2 to 12 V.

2 x 12V 21W lightglobe

2 x fixed resistors (2 ohm or 5 ohm)

6 x conducting leads with suitable attachments

2 x tapping key switches

1 x ammeter

1 x voltmeter

Or alternatively use two multimeters, one on ammeter setting and one on voltage setting.


Starting with circuit 1, construct the circuit and carry out the trial as shown below:


Circuit 1.


Circuit 2.


Circuit 3.

The variable power supply was set to 2 V. The circuit was turned on briefly by closing the switch to complete the circuit and observations of the meter reading made. This was repeated for each further setting on the variable power supply until 12 V was reached or till one of the meters deflected full scale.

For circuit 2 move the voltmeter so that you take readings across both light globes. Careful observations on the appearance of the light globe(s) and any reading on the ammeter were made and recorded. Design a table that would enable easy communication of your observations to someone else not doing this investigation.

The observations were recorded.

This was repeated for each of the other circuits, i.e. 2 . Consider whether this is the best design for the circuit.

Both circuits 1 and 2 are called series circuits. Design a parallel circuit using two light globes. Check the paper circuit design with your teacher, build the circuit have it checked for safety with your teacher and operate it.

How does the voltage dropped across each light globe compare to the same setting range on the power supply? The results were recorded, analysed, and then a conclusion written. 



  1. For each of the circuits, what did you notice as the voltage from the power supply was increased?
  2. Based on your results, which of the three circuits had the highest resistance? Explain your answer.
  3. Considering the globes used in the experiment were all the same, can you see any relationship evident for the number of globes compared to the total resistance of the circuit?
  4. Describe any obvious differences you observed for circuit 2 compared to circuit 3 when the voltage from the power supply was at the highest settings. Can you explain why these differences occurred in relation to whether the globes are set in series or parallel?
Electrical cord