AST Lec 9: Light

The transmission of energy as light.

Emission

Light bouncing off a reflective surface, going from one direction to another at a specific angle

Reflection

The reflection of light in all directions.

Scattering

When a certain colour of light from a light source hits an object and is not reflected or scattered.

Absorption

When light travels though a transparent object.

Transmission

Explain the effect that a quartz glass prism has on light.

The glass changes the direction of the light coming in. Violet light is bent the most, while red light is bent the least. Tells us that white light is actually made up of these colours combined.

How do screens produce different colours? Why do they use the 3 colours that they do?

Screens emit different combinations of red, blue, and green lights to create different colours. Different cones in the retina detect those 3 colours, signalling to the brain an in-between colour when diff combinations are used.

Why does a leaf appear green?

It scatters green light and absorbs other colours.

A piece of semi-transparent red plastic is placed in front of a spotlight. The light spot on a white stage appears red because the filter:

Transmits red light, and absorbs other colours

The distance between electromagnetic wave peaks.

Wavelength

The height of electromagnetic wave peaks.

Amplitude

How often the electromagnetic wave peaks arrive per unit of time.

Frequency

Red light has a longer wavelength than blue light. In a vacuum, red light…

…has a lower frequency, but the same speed

What is Thermal Radiation?

When a source of energy as heat also emits energy as light.

How does the temperature of an object affect its colour?

Hotter objects are brighter and have cooler colours, cooler warm objects have wrmer colours.

Explain how an ear thermometer determines your temperature.

The thermometer measures the infra-red light given off by your ear drum.

What unit of temperature is used, and what is its relative measurement? What is room temp at this measurement?

Degrees Kelvin tells you how many decrees above Absolute Zero (where atoms stop moving) the temp is. Room temp is 300*K.

Consider 2 stars equally far away, and which have the same radius. One is hotter than the other. Which is true?

The hotter star will appear bluer and brighter