Physics clicker question: internal energy of different mass samples

Physics 205A, Spring Semester 2009
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Conceptual Question 14.20 (extended)

Students were asked the following clicker question (Classroom Performance System, einstruction.com) at the start of their learning cycle:

A 50 g iron sample and a 10 g iron sample are both at room temperature (25 degrees C). Which sample has more internal energy?
(A) 50 g iron sample.
(B) 10 g iron sample.
(C) (There is a tie.)
(D) (I'm lost, and don't know how to answer this.)

Sections 30880, 30881
(A) : 14 students
(B) : 9 students
(C) : 4 students
(D) : 1 student

This question was asked again after displaying the tallied results with the lack of consensus, with the following results. No comments were made by the instructor, in order to see if students were going to be able to discuss and determine the correct answer among themselves.

Sections 30880, 30881
(A) : 27 students
(B) : 0 students
(C) : 1 student
(D) : 0 students

Correct answer: (A)

Adding heat (Q) to an object increases its internal energy, resulting in increasing its temperature. If both samples could be at absolute zero, then they would possess the same (zero) internal energy. The larger sample would require more heat to be added in order to raise its temperature up to room temperature, as expressed as:

Q = delta(internal energy) = m*c*delta(T),

where c is the (mass) specific heat (same for both samples), and delta(T) is the same for both samples.

Pre- to post- peer-interaction gains:
pre-interaction correct =50%
post-interaction correct = 96%
Hake, or normalized gain = 93%