Physics – Light and Geometric Optics

Incandescence: Light given off when an object is very hot. Luminescence: Light given off when an object is not heated. There are several types of luminescence:  Chemiluminescence – some chemical reactions emit light, but no heat.  Electric Discharge – gases in a tube absorb electrical energy and emit light.  Fluorescence - gases in a tube absorb electrical energy and emit ultraviolet light.

Wavelength - the distance from one place in a wave to the next similar place on the wave; for example, the distance from crest to crest.

The Electromagnetic Spectrum

Light is a form of energy. Visible light is only a tiny fraction of the energy that surrounds us every day. We are also surrounded by invisible light-like waves, which together with visible light are called electromagnetic radiation.

Electromagnetic radiation is a wave pattern made of electric and magnetic fields that can travel through empty space. The different types of electromagnetic waves make up what is called the electromagnetic spectrum

Radio Waves - Uses AM/FM radio signals Television signals Radar Satellite communications Magnetic resonance imaging machines (MRI).

Microwave ovens Satellites Cell phone signals Microwave - Uses

Security systems (burglar alarms, motion sensors) Lasers Night vision goggles Provides heat to keep food warm in restaurants. Infrared Light - Uses

Causes skin to tan Increases risk of skin cancer Stimulates the production of Vitamin D Kills bacteria in food / water Used in detective work to reveal the presence of substances that cannot be seen under visible light. Ultraviolet Light - Uses

Able to go through most things except bone and lead. Security equipment (i.e. At airports) Medical imaging (X-ray machine) X-Rays- Uses

Used to sterilize medical equipment. Cancer treatment (radiation therapy) Product of nuclear decay. Gamma Rays - Uses

White light separates into the colours of the rainbow, including red, orange, yellow, green, blue, and violet (ROY G BV). The range of different colours of light is called the visible spectrum. The difference between colours of light is that each colour has a different wavelength and frequency.

ColourFrequency (Hz)Wavelength (nm) Red4.3 x Orange5.0 x Yellow5.2 x Green5.7 x Blue6.4 x Violet7.5 x  Longer  Shorter

ACTIVITY: What Is White Light Made Of?

Reflection, Absorption, Transmission Transmission: Light passes through an object and continues travelling. Example: Clear glass. Absorption: Light is absorbed by (remains in) the object and turned into heat. Reflection: Light bounces off the object and travels in another direction.

Reflection — Light Changes Direction In A the person sees the object because light travels to their eyes. B shows that light must travel from a source (the lamp) and then reflect off the object toward the eye.

Absorption – Light Is Converted to Heat The “E” in the image above appears black because the ink absorbs all of the light that hits it. No light reaches your eyes from the printed “E”.

Transparent, Translucent, and Opaque Objects Transparent materials absorb and reflect very little light. Example: a clear window. Translucent materials allow light to pass through but scatters it in different directions. Opaque objects absorb and reflect light, but they do not transmit it.

Objects can absorb some colours and reflect or transmit others. Opaque objects either absorb or reflect light. The colour an object is determined by: the colours (or wavelengths) of light that are reflected by its surface and the colours that are absorbed by the object. Under white light, the tomato appears to be red because only the red wavelength is reflected. Under blue light, the tomato appears to be blue.

Objects can absorb some colours and reflect or transmit others. The colour of an object is determined by: which colours (or wavelengths) of light are reflected by its surface, and which colours are absorbed by the object. The apple reflects only red light. The pepper reflects only green light.

ACTIVITY: Exploring the properties of light (Pin hole camera) Rays of light travel in a straight line. As a result, the rays investigated in this activity will cross at the pinhole. Q1. What did you find out? -Light from higher points on the object would travel in a straight line through the pinhole, and end up low on the image. - Light from lower points on the object would travel in a straight line through the pinhole and end up high on the image.

CLASSWORK Textbook: - Read and make notes (p.277 to 283) (p.288 to 291) - P. 283 “Check Learning” # 1-3 Complete handouts: - Incandescence and Luminescence - Light - Reflect, Absorb, Transmit QUIZ on WEDNESDAY