AP Labs

Many of you missed some important points in the power and specific heat labs.

1) Power labs: the major reason for the increase in power in shorter times is not the increase in KE which has a relatively small effect since the work is till dominated by delta PE. Rather it is the decrease in the denominator in P =(delta PE+delta KE)/delta t.

2) Purpose was to show how power is affected by change in delta KE, delta PE and most particularly delta t.

2) Specific heat lab

a) Largest source of error is in Tf-Tw since this was between 5 and 10 deg C and error in reading is about 1/2 a deg so errors here alone are between 5 and 20 %.

b) most got it right that purpose was to prove conservation of thermal energy, that Q out of hot = Q into cold and some of you even discussed how the energy was exchanged via collisions.
c) many of you still do not write explicit equations. Every lab should have had an equation such as cblock = (Mw cw delta Tw + Mcan ccan delta T can [same as delta Tw])/(Mblock delta T block)

d) some of you think all silvery metals in room 506 are aluminum. If your block had a mass much more than 88 g it was not aluminum. Zinc or steel would have masses more like 250 g. These metals have cs near 390 and would give you reasonably small errors.