P14: Light

Convex lens

Curves outwards to focus parallel rays of light to a principal focus point.

Concave lens

Curves inwards causing parallel rays of light to diverge away from a focal point.

Focal length

The distance from the center of the lens to the principal focus.

Real image

An image formed where light rays actually cross and can be projected onto a screen.

Virtual image

An image formed where light rays only appear to come from and cannot be projected onto a screen.

Convex image beyond 2F

Produces a real inverted diminished image located between F and 2F.

Convex image between F and 2F

Produces a real inverted enlarged image located beyond 2F.

Convex image closer than F

Produces a virtual upright enlarged image on the same side as the object acting as a magnifying glass.

Concave lens image properties

Always produces a virtual upright diminished image regardless of object position.

Magnification definition

The ratio of image height to object height which has no units.

Specular reflection

Reflection from a smooth surface where parallel light rays reflect together in one direction.

Diffuse scattering

Reflection from a rough surface where light rays scatter in many different directions.

How is the color of an opaque object determined?

Determined by which wavelengths of light are absorbed and which wavelengths are reflected back to the eye.

Transparent material

Allows light rays to pass directly through without scattering so objects behind are clear.

Translucent material

Allows light to pass through but scatters rays in different directions so objects appear blurry.

Color filters

Transmit only specific wavelengths of light matching their color while absorbing all other wavelengths.

Perfect black body

A theoretical object that absorbs all electromagnetic radiation incident on it without reflecting or transmitting any.

Black body emission

A perfect black body is also the best possible emitter of radiation.

Black body radiation curve

As temperature increases the total power emitted increases and the wavelength of peak intensity becomes shorter.

Constant temperature equilibrium

Occurs when an object emits radiation at the exact same rate as it absorbs radiation.

Earth temperature balance

Depends on the balance between absorption of solar radiation and emission of infrared radiation back into space.