Optics
Simple magnifier (angular)
At the focal plane, a converging lens sends parallel rays to a relaxed eye; M = N/f (N = 25 cm).
Simple magnifier (angular) — interactive Optics simulation. A single converging lens held near the eye gives angular magnification M = N/f (N = 25 cm). Free browser-based virtual physics lab with live SI measurements and a guided tutorial.
Angular magnification
With the object at the focal plane, a converging lens sends parallel rays to a relaxed eye; M = N/f (N = 25 cm).
For relaxed-eye viewing, place the object at the focal plane of a short-focal-length lens. The emerging rays are parallel, the virtual image is at infinity, and the angular magnification is M = N/f for N = 25 cm.
- M = N/f
- N = 25 cm
Investigation brief
Plan the question before you open the lab
The brief mirrors the prerendered page: driving question, competing predictions, variable roles, governing laws, setup, analysis and extension prompts remain visible and in this order.
Driving question
A simple magnifying glass, used with a relaxed eye, has its object placed exactly at the lens's focal point. Does a shorter-focal-length lens give a higher or lower angular magnification?
Predictions to weigh
- A shorter focal length gives lower magnification.
- Magnification doesn't depend on the lens's focal length.
- Higher — a shorter focal length lets you get much closer to the object than the eye's unaided near point would allow, producing a larger apparent angular size.
Variable roles
What you set:
- Lens focal length f (cm)
What you measure:
- Angular magnification M
How the investigation runs
- Open the simple-magnifier preset and press Reset. The object sits exactly at the lens's focal point (relaxed-eye viewing, virtual image at infinity).
- Enable the angular-magnification readout.
- Set the lens's focal length for each trial and record the resulting angular magnification.
Governing equation
Simple Magnifier Angular Magnification — M = N/f
A magnifying glass used with a relaxed eye and its object at the focal point achieves angular magnification M = N/f, where N = 25 cm is the standard near-point distance. Shorter focal length means higher magnification.
What the printable worksheet asks students to work out
- For one trial, compute M = N/f using the standard near-point distance N = 25 cm. Compare to the table.
- Explain why a shorter focal length gives higher magnification: it lets the relaxed eye view the object from much closer than its own unaided near point would ever allow, making the object subtend a much larger angle.
Where this shows up beyond the lab
- Very short focal length magnifiers (giving high M) also have very short working distances (the object nearly touches the lens), which becomes impractical past a certain magnification. Explain why jeweler's loupes and simple hand magnifiers rarely exceed about 10×–20×.
- For much higher magnification than a simple lens can practically achieve, optical designers switch to compound systems (like the compound-microscope experiment). Explain why chaining two moderate-magnification stages together, rather than using one extremely short-focal-length lens, is the practical solution.
- AP Physics 2 — Unit 13: Geometric Optics
- General High School Physics — Light & optics
- NGSS High School Physics — Wave properties
- Welcome to Simple Magnifier
- Select the object
- Press Play
- Near-point magnification
- Open the Properties panel
- You did it!
Open the interactive simulation to build the scene, press Play, and explore with live measurements and a guided tutorial.