## 20160327

### Physics midterm question: largest possible diverging lens image

Physics 205B Midterm 1, spring semester 2016
Cuesta College, San Luis Obispo, CA

An object is allowed to be placed at any distance in front of a f = –12.0 cm diverging lens. Discuss where the object must be placed in front of the lens in order to obtain the largest image possible. Explain your reasoning by using ray tracings and/or thin lens equations, the properties of lenses, images, and magnification.

• p:
Correct. Proves that the object should be as close to the diverging lens as possible in order to obtain the largest image (largest linear magnification factor) using at least one of these methods:
1. two or more calculations of the image distances produced by different object distances, finds the resulting respective image sizes or linear magnification factors (or one calculation is sufficient, provided discussion on how the calculation would change if the object were brought closer to the lens), and;
2. drawing two or more carefully, properly scaled ray tracing diagrams (or one diagram is sufficient, provided discussion on how the diagram would change if the object were brought closer to the lens).
• r:
As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes.
• t:
Nearly correct, but argument has conceptual errors, or is incomplete.
• v:
Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Some garbled attempt at applying properties of lenses, images, and linear magnification.
• x:
Implementation/application of ideas, but credit given for effort rather than merit. No clear attempt at applying properties of lenses, images, and angular magnification.
• y:
Irrelevant discussion/effectively blank.
• z:
Blank.
Sections 30882, 30883
Exam code: midterm01rx1C
p: 19 students
r: 6 students
t: 9 students
v: 8 students
x: 1 student
y: 0 students
z: 0 students

A sample "p" response (from student 5433):