Grade 8 Science

Unit 3: Optics

Chapter 4: Properties of Light

Can light be produced in different ways:

  1. ______
  2. ______
  3. ______
  4. ______

The Nature of Light

1)Pythagoras

  • A Greek philosopher
  • Believed that ______

______

  • The eyes could ______and see the objects

2)Galileo

  • He was the first person to ______

______

  • He used lanterns on hilltops to ______

______

3)Michelson

  • He was the first person to ______

______

  • He shone a light on ______that reflected to a ______.
  • He used the distance and reflection time to ______

______

Light:______

Speed: Light vs. Sound

  • Light = ______(______)
  • Sound = ______(______)
  1. Explain why you see the lightning before you hear it.

______

  1. Is it possible for stars to be burned out even though we are seeing them in our night sky?

Explain.

______

Light technologies include:

  • ______
  • ______
  • ______
  • ______
  • ______

Foldable – Tab 1 – The nature of light

Inside tab:

  • Give a brief description of the discoveries made by Pythagoras, Galileo, and Michelson
  • Define light
  • State the speed of light
  • List four technologies that involve light

Outside tab:

  • Draw a picture of a microscope

Pg 137 #8

Properties of waves

A wave is a ______

______.

The wave model

  • Explains that light is a type of wave that travels through empty space and ______

Properties of waves

  • A wave is ______or ______that transfers energy through matter or space, without causing any permanent ______.

The wavelength - ______

______. It is measured in metres.

Frequency -______

______.It is measured in cycle per second or Hertz (Hz).

The higher the frequency, ______the wave.High frequency waves have ______wavelengths.

Low frequency waves have ______wavelengths.

Page 147 # 4 and 8

Foldable- Tab: Properties of Waves

Outside tab:

Draw a typical wave and label the following:

  • crest
  • trough
  • wavelength

Inside tab:

  • Define wave, wavelength and frequency
  • The longer the wavelength, the ______the frequency.
  • The shorter the wavelength, the ______the frequency.

Properties of Light

  1. ______

______

  1. ______
  1. ______
  1. ______

Example: white light separates into the colours of the rainbow

  1. ______

- ______

- ______

Example: light from the Sun and stars

  1. ______.

Visible Light

  • White light is a ______.

Visible light spectrum______

______

Can be seen due to the dispersion of light through a prism

The constituent colors of white light are:

R______(Smallest refraction, longest wavelength)

O______

Y______

G______

B______

I______

V______(Greatest refraction, shortest wavelength)

  • The colour we see is the colour that is being reflected. All other wavelengths are absorbed.

PG. 155 #2-5, 7, 9, 10

Foldable- Tab: Properties of Visible Light

Inside: State the 6 properties of visible light

Outside: Draw a picture that relates to one property of visible light

Light and the Electromagnetic Spectrum

Electromagnetic Radiation

- The transmission of energy in the form of waves that extend from ______waves (longest) to ______rays (shortest).

Types of Electromagnetic Radiation (in order of decreasing wavelength)

1. Radio waves

  • ______
  • ______
  • ______

- Longer radio waves can help us see inside our bodies and diagnose illnesses. Example: MRI machines

2. Microwaves

- A type of radio wave that has the ______wavelength and ______frequency.

Examples: microwave ovens, telecommunications, and radar

3. Infrared Waves

Compared to visible light:

  • ______
  • ______
  • ______

- Also called heat radiation

Example: motion sensors, remote control

4. Visible Light

- ______

Example: microscopes

5. Ultraviolet Light

Compared to visible light:

  • ______
  • ______
  • ______

Example: sun tanning

6. X-Rays

Compared to visible light:

  • ______
  • ______
  • ______

Example: medical detection

7. Gamma Rays

They have:

  • ______
  • ______
  • ______

Gamma rays result from nuclear reactions.

They are used in radiation therapy to kill cancer cells.

Is electromagnetic Radiation dangerous?

  • Higher energy electromagnetic radiation (______) is more harmful than lower energy (______).
  • The atmosphere protects us by ______higher energy radiation

Electromagnetic Radiation / Positive Effects / Negative Effects
Radio Waves
X-Rays
Ultraviolet
Gamma Rays

Pg 167 # 3, 10, 11 and 12

Foldable – Tab: Light and the Electromagnetic Specturm

Inside tab:

  • List the 7 types of electromagnetic radiation in order starting with the
    longest wavelength and shortest frequency
  • Which type of electromagnetic radiation is the most harmful?
  • Which type of electromagnetic radiation causes sunburns?
  • Which type of electromagnetic radiation has the lowest energy?

Outside tab:

  • Draw two objects that rely on radio waves