Optics and Lens Properties Review

Vocabulary-style flashcards covering Snell's Law, reflection and refraction rules, SALT characteristics for mirrors and lenses, and lens sign conventions.

Snell's Law (Full Law)

The formula used to calculate refraction: $n_1\text{sin}(\theta_1) = n_2\text{sin}(\theta_2)$. It is considered safer for tests than the special case formula used only for air.

Concave Mirror at Principal Focus (F)

When an object is placed at F, reflected rays are parallel and the image forms at infinity; often described as 'no image formed' because it cannot be projected.

Converging Lens at Principal Focus (F)

Refracted rays emerge parallel and the image forms at infinity.

Refraction: Bending Toward the Normal

Occurs when light enters a material with a higher refractive index and slows down.

Refraction: Bending Away from the Normal

Occurs when light enters a material with a lower refractive index and speeds up.

Conditions for Total Internal Reflection (TIR)

1. Light starts in a higher $n$ material. 2. Light moves toward a lower $n$ material. 3. Incident angle > critical angle.

SALT for Plane Mirror

Size: Same size; Attitude: Upright; Location: Same distance behind mirror; Type: Virtual; includes lateral inversion (left-right reversal).

SALT for Convex Mirror

Size: Smaller; Attitude: Upright; Location: Behind mirror; Type: Virtual (Always no exceptions).

SALT for Diverging Lens

Size: Smaller; Attitude: Upright; Location: Same side as object; Type: Virtual (Always no exceptions).

Real Image

An image where rays actually meet, can be projected on a screen, and is usually inverted.

Virtual Image

An image where rays only appear to meet, cannot be projected on a screen, and is usually upright.

Focal Length ($f$) Sign Convention

Positive for a Converging Lens; Negative for a Diverging Lens.

Image Distance ($d_i$) Sign Convention

Positive for a Real Image; Negative for a Virtual Image.

Image Height ($h_i$) and Magnification ($m$) Sign Convention

Positive if the image is Upright; Negative if the image is Inverted.

Converging Lens (Convex Lens) Physical Description

A lens that is thicker in the middle and thinner at the edges; it refracts parallel light rays inward to meet at the Principal Focus (F).

Optical Centre (O)

The centre of the lens; any light ray passing through this point continues in a straight line without refracting.

Converging Lens SALT: Object Beyond 2F

Size: Smaller; Attitude: Inverted; Location: Between F and 2F on the opposite side; Type: Real.

Converging Lens SALT: Object At 2F

Size: Same size; Attitude: Inverted; Location: At 2F on the opposite side; Type: Real.

Converging Lens SALT: Object Between F and 2F

Size: Larger; Attitude: Inverted; Location: Beyond 2F on the opposite side; Type: Real.

Converging Lens SALT: Object Between F and Lens

Size: Larger; Attitude: Upright; Location: Same side as object; Type: Virtual (used as a magnifying glass).

Diverging Lens (Concave Lens) Physical Description

A lens that is thinner in the middle and thicker at the edges; it refracts parallel light rays outward so they appear to originate from a focal point behind the lens.

Common Uses of Diverging Lenses

Glasses for myopia (nearsightedness), door peepholes, and some camera systems.

Common Uses of Converging Lenses

Magnifying glass, camera, human eye, microscope, and projector.