Cuesta College, San Luis Obispo, CA
Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 23.63
A Physics 205B student places a object 22 cm in front of (to the left of) a converging lens (f = +11 cm). Discuss why the size of resulting image will be exactly the same size as the original object. Explain your reasoning by using the properties of lenses, thin lens equations and/or ray tracings.
Solution and grading rubric:
Correct. Image will be the same size as the original object because:
- from the thin lens equation, the image distance q will be the same as the object image distance p;
- and from the linear magnification equation, the image height h' will be -h∙q/p, which makes the image the same size as (but inverted from) the original object.
As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes. Typically shows that p = q, but does not explicitly relate this to how the image and object sizes compare.
Nearly correct, but argument has conceptual errors, or is incomplete.
Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner.
Implementation/application of ideas, but credit given for effort rather than merit.
Irrelevant discussion/effectively blank.
Sections 30882, 30883
Exam code: finalLd0c
p: 16 students
r: 18 students
t: 2 students
v: 2 students
x: 1 student
y: 1 student
z: 3 student
A sample "p" response (from student 5425):
A sample "r" response (from student 1675):