To calculate the change in temperature, subtract the initial temperature from the final temperature. Example: 84.2 degree Fahrenheit - 41 degrees Fahrenheit = 43.2 degrees Fahrenheit. The temperature from morning to afternoon changed by 43.2 degrees Fahrenheit.
It needs 12 volts so it will be the standard modern power supply provides 12 volts of power.
Ideal current sources provide a specified current regardless of the voltage difference across the device. Ideal current sources can, like ideal voltage sources, provide infinite power; all real sources will provide only limited power to the circuit; as with voltage sources, this is a topic for later projects.