Final answer:
To measure current, the Vernier current probe or an ammeter must be connected in series with the component or circuit to be tested, ensuring that it is placed between the positive terminal of the voltage source and the component, and the circuit is then completed by connecting to the negative terminal.
Step-by-step explanation:
To measure electrical current in an experiment, a Vernier current probe or an ammeter must be placed in series with the component or the part of the circuit you are investigating. For example, if you are testing the conductivity of solid crystals or solutions, you will complete the circuit by attaching crocodile clips to each end of the crystal, or by placing two carbon rods into the solution with clips attached to them. Then, to accurately obtain a current reading, connect the positive terminal of the voltage source to the input of the ammeter and the output of the ammeter to the component or one of the rods in the solution, and finally complete the circuit by connecting it back to the negative terminal of the voltage source.
When confirming Kirchhoff's junction rule, you would measure the current at three points in the circuit where currents divide or combine. This is to ensure that the total current entering a junction equals the total current leaving that junction, which is the essence of Kirchhoff's junction rule. Lastly, remember that a voltmeter, unlike an ammeter, is always connected in parallel to the component whose voltage you wish to measure, due to its high resistance.