Cuesta College, San Luis Obispo, CA
Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 23.63
An object can be placed either 16 cm or 14 cm in front of a f = +15 cm converging lens. Decide which object distance will result in the largest image (regardless of being real/virtual, or inverted/upright), or if there will be a tie. Show your work and explain your reasoning using the properties of lenses, thin lens equations and/or ray tracings.
Solution and grading rubric:
Correct. Compares the linear magnification ratios of both object distances using one of two methods:
- determines the image distances produced by these objects, then sets up the ratio m = –di/do to find their respective linear magnification factors;
- a carefully, properly scaled ray tracing diagram.
Nearly correct, but includes minor math errors. May have sign errors or inverse errors.
Nearly correct, but approach has conceptual errors, and/or major/compounded math errors. At least enough steps are shown that would theoretically result in a complete answer, multiple errors (or omission of last step of finding m = –di/do ratio) notwithstanding. May draw a ray tracing diagram that does not have its object distances properly scaled with regards to the focal points, but at least makes a consistent conclusion based on the faulty scaling of object positions.
Implementation of right ideas, but in an inconsistent, incomplete, or unorganized manner. Ray tracings have real images for both cases, etc.
Implementation/application of ideas, but credit given for effort rather than merit.
Irrelevant discussion/effectively blank.
Sections 30882, 30883
Exam code: midterm01p34K
p: 21 students
r: 6 students
t: 13 students
v: 6 students
x: 1 student
y: 0 students
z: 0 student
A sample "p" response (from student 8984):