Optics
Concave mirror — real image
Object beyond f of a concave mirror: a real, inverted image in front of the mirror.
Concave mirror — real image — interactive Optics simulation. Object beyond f of a concave mirror: a real, inverted image in front of the mirror. Free browser-based virtual physics lab with live SI measurements and a guided tutorial.
Concave mirror
Object beyond f of a concave mirror: a real, inverted image in front of the mirror.
Concave mirrors obey the same sign conventions as lenses. With the object beyond the focal length, reflected rays converge to a real inverted image in front of the mirror—used in shaving mirrors at moderate distance and in reflecting telescopes.
- 1/f = 1/d_o + 1/d_i
- Real inverted image
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 concave mirror focuses light like a converging lens. Does moving the object farther from a concave mirror move its real image closer to the mirror's focal point, the same way it does for a lens?
Predictions to weigh
- No — a farther object moves the image farther from the mirror.
- Mirrors and lenses follow completely different imaging rules.
- Yes — the same 1/f = 1/d_o + 1/d_i relationship applies, so a farther object gives an image closer to the focal length.
Variable roles
What you set:
- Object distance d_o (cm)
What you measure:
- Image distance d_i (cm)
- Magnification m
How the investigation runs
- Open the concave-real preset and press Reset. The mirror's focal length is fixed at 15 cm.
- Enable the image-distance and magnification readouts.
- Set the object distance for each trial and record the image distance and magnification.
Governing equation
Mirror Equation — dᵢ = dₒ·f/(dₒ − f)
A concave (converging) mirror obeys the same imaging law as a converging lens: 1/f = 1/d_o + 1/d_i, with m = −d_i/d_o. The mirror's focal length is positive, matching the lens sign convention.
What the printable worksheet asks students to work out
- For one trial, compute d_i from 1/f = 1/d_o + 1/d_i using f = 15 cm, then m = −d_i/d_o. Compare both to the table.
- Explain why the mirror equation is mathematically identical in form to the thin-lens equation — both use the same 1/f = 1/d_o + 1/d_i relationship, even though a mirror reflects light rather than refracting it.
Where this shows up beyond the lab
- A shaving or makeup mirror is concave, held closer than its focal length to give an enlarged virtual image (like the magnifier experiment). This experiment instead keeps the object beyond f, giving a real, inverted image. Explain when you'd want each configuration.
- Every image in this experiment has negative magnification. Explain, using a concave mirror's actual reflecting geometry, why a real image formed by a concave mirror is inverted, just like a converging lens's real image.
- AP Physics 2 — Unit 13: Geometric Optics
- General High School Physics — Light & optics
- NGSS High School Physics — Wave properties
- Welcome to Concave Real
- Select the object
- Press Play
- Real mirror image
- 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.