If a piece of aluminum is heated from 30.0°C to 50.0°C, what is the value of ∆T?
The value of ∆T ( change in Temperature), would be 20 degree C.
∆T means the change in Temperature. The final temperature minus the starting temperature gives the change in temperature.
50-30 = 20 degree C.
In this case, we have a positive 20 degree C which means we gained energy. If it was a negative value, you would lose energy.