How can you tell if a circuit containing a conductor is closed without using an ammeter?

You can check the closed circuit without using an ammeter in the following ways:
* Through the presence of a magnetic field.
* Using other electrical appliances.
* Through heating.

Checking the closed circuit through a magnetic field
According to the laws of physics, any closed circuit has a magnetic field.
In order to check if it is closed, you can take a compass.
In the event that we attach the compass to the circuit, the arrow pointing north will deviate from the usual direction.
In addition, the magnetic field can be checked with a needle hanging from a thread.
In this case, if a current flows through the conductor, it will deviate from the conductor and rotate in different directions.

Checking with other electrical devices
To check the closed circuit and the presence of current in it, you can use a voltmeter.
In the event that a current flows through the circuit, it will cause resistance.
The product of resistance and current will show the voltage value on the voltmeter, which will differ from 0, because:
U = I * R.
To check that the circuit is closed, you can ring the circuit using a two-conductor incandescent lamp.
If current passes through the circuit, the lamp will light up.
You can also check the presence of current using an ohmmeter connected to a conductor or using a special screwdriver.

Check through heating
Since resistance occurs in the circuit through which the current flows, it causes heating of the conductor.
If you take a sufficiently sensitive thermometer or pyrometer, then the temperature readings on it when directed or applied to the conductor will differ from the value of the ambient temperature.