Explain the significance of the thermometer, the electric heater, and the power

This question appear incomplete

Explanation:

This question appear incomplete. However, the significance/functions of the "instruments" mentioned (in the completed question) can be predicted since these "instruments" generally have specialized function.

A thermometer is used to determine the temperature of a substance or an object. The electric heater uses electricity to produce heat (which can be utilized for different purposes). The power supply is used to supply electricity for instruments/appliances that may require electricity to function.

The answer is direct current.

Explanation:

There are two types of currents: Direct Current (DC) and Alternate Current (AC)

Direct current flows in one direction all the time and batteries are the best example for direct current supply. If you look at a typical flashlight battery, you will see the marked poles "+" and "-". When you connect the battery, current flows from the positive pole, through the circuit of the flashlight and back to the negative pole, ALWAYS IN THE SAME DIRECTION.

On the other hand, alternate current reverses direction periodically and typically in a sine wave form. But it´s not always the case, you could have square waves, triangular and other types. They type of current you get at home is AC.