Ray Optics
Ray Optics is a free interactive simulation from StudyFi Lab. It runs right in your browser, with no sign-up and nothing to install.
Lenses, mirrors, refraction and a prism
Experiments
Converging lens
A converging lens bends parallel rays through its focal point F′. Three principal rays find the image: the ray parallel to the axis passes through F′, the ray through the centre goes straight on, and the ray through F leaves parallel to the axis. The lens equation is 1/f = 1/dₒ + 1/dᵢ and the magnification is m = −dᵢ/dₒ.
Try this: Move the object to 2f — the image is the same size and upside down. Then bring it inside the focal length.
Diverging lens
A diverging lens spreads rays out as if they came from the focal point F′ on the object’s side. Their backward extensions (dashed) meet on that side, so the image is always virtual, upright and smaller. The focal length is negative and 1/f = 1/dₒ + 1/dᵢ still holds.
Try this: Drag the object far away and right up to the lens — the image stays between the lens and F′ and never turns over.
Concave mirror
A concave mirror reflects parallel rays through its focal point F, halfway to the centre of curvature (f = R/2). The ray to the vertex reflects at the same angle, and the ray through F returns parallel to the axis. The lens equation holds here too, 1/f = 1/dₒ + 1/dᵢ; a real image forms in front of the mirror.
Try this: Bring the object between F and the mirror — you get a magnified upright image behind it, like in a make-up mirror.
Convex mirror
A convex mirror reflects rays apart, as if they came from a focal point behind the mirror. Their extensions meet behind it, so the image is always virtual, upright and smaller. The focal length is negative and 1/f = 1/dₒ + 1/dᵢ holds — that is why these mirrors are used at road junctions and on cars, where they show a wide view.
Try this: Shorten the focal length (a more curved mirror) — the image shrinks, so more of the surroundings fits in.
Refraction and total internal reflection
At the boundary between two media a ray is partly reflected and partly refracted by Snell’s law, n₁ · sin θ₁ = n₂ · sin θ₂. Entering a denser medium it bends towards the normal, entering a less dense one it bends away. Going into the less dense medium beyond the critical angle θc = arcsin(n₂/n₁), the refracted ray disappears and total internal reflection takes over.
Try this: Set water on top and air below and increase the angle — beyond 48.8° all the light is reflected back.
Dispersion in a prism
The refractive index of glass depends on the wavelength: by Cauchy’s formula n(λ) = A + B/λ², violet light has a higher index than red. A prism therefore bends each colour by a different amount and white light fans out into a spectrum. The deviation δ = θ₁ + θ₂ − A is largest for violet.
Try this: Rotate the prism and look for the smallest deviation — then the beam inside runs parallel to the base.
Frequently asked questions
What is Ray Optics?
Ray Optics is a free interactive simulation from StudyFi Lab. It runs right in your browser, with no sign-up and nothing to install. Lenses, mirrors, refraction and a prism
Is Ray Optics free?
Yes. Ray Optics is completely free. It works in the browser on computers, tablets and phones, and you do not need an account.
What can I explore in Ray Optics?
Converging lens, Diverging lens, Concave mirror, Convex mirror, Refraction and total internal reflection, Dispersion in a prism.
What does the “Converging lens” experiment show?
A converging lens bends parallel rays through its focal point F′. Three principal rays find the image: the ray parallel to the axis passes through F′, the ray through the centre goes straight on, and the ray through F leaves parallel to the axis. The lens equation is 1/f = 1/dₒ + 1/dᵢ and the magnification is m = −dᵢ/dₒ.
What does the “Diverging lens” experiment show?
A diverging lens spreads rays out as if they came from the focal point F′ on the object’s side. Their backward extensions (dashed) meet on that side, so the image is always virtual, upright and smaller. The focal length is negative and 1/f = 1/dₒ + 1/dᵢ still holds.
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