Physics 8 Notes

Question 1

What is absorption?

Answer 1

Absorption is the process in which light is absorbed and trapped in an object as heat.

Question 2

What is reflection?

Answer 2

Reflection is the process in which light rays bounce off a surface.

Question 3

What are the Laws of Reflection?

Answer 3

1) The Angle of Reflection (r) equals the Angle of Incidence (i)
2) The incident ray and the reflected ray are on opposite sides of the normal.
3) The incident ray, the normal, and the reflected ray all lie on the same plane.

Question 4

The Law of Reflection

Answer 4

1. The incidence ray: The incoming ray; the light ray travelling towards the reflecting surface
2. The angle of incidence: The angle between the incident ray and the normal
3. The reflected ray: The outcoming ray - the light ray that has bounced off the reflecting surface
4. The angle of reflection: The angle between the reflected ray and the normal
5. The Normal: a line perpendicular to a surface (ex. a mirror)

Question 5

What is transmission?

Answer 5

Transmission is the process in which light rays pass through an object. Some materials allow different amounts of light to pass through. Most light rays pass through, and the rest are scattered in different directions.

Question 6

Plane and Curved Mirrors - General Facts

Answer 6

Plane mirror: an extremely smooth, flat reflective surface.
When light shines on an object, it reflects off all points of the object in every direction.
Some light rays reach your eyes if you are looking at the mirror and your brain assumes that light has travelled in a straight line and thinks the image is behind the mirror.
You can find out where the image appears to be by extending the reflected rays backwards until they meet.
A mirror plane produces an image that is nearly identical to the object: The image is reversed!

Question 7

Four Characteristics of Images in a Mirror Plane

Answer 7

A. Location: The image may be closer to, farther from, or the same distance from the mirror as the object
B. Size: The image may be the same size as, larger than, or smaller than the object.
C. Orientation: An image may be upright or inverted (upside down)
D: Type:
Real (it is formed when reflected rays meet. It is located in front of the mirror.)
Virtual (it is formed when extended rays meet. It is behind the mirror.)

Question 8

Images in Concave Mirrors

Answer 8

Focal point: the point where the reflected light rays come together
When light rays reflect off a concave mirror, they converge at the focal point.
The characteristics (location, size, orientation, type) of the image formed by concave mirrors depend on where it is located compared to the surface of the mirror and the focal point.

Question 9

Images in Convex Mirrors

Answer 9

When light rays reflect off a convex mirror, they diverge (they spread out in different directions)
The characteristics (location, size, orientation, type) of the image formed by convex mirrors DO NOT depend on where it is located compared to the surface of the mirror and the focal point.

Question 10

What is EMR (Electromagnetic Radiation)?

Answer 10

EMR is a kind of radiation including visible light, radio waves, microwaves, gamma rays, infrared radiation, UV radiation, and X-rays. It is a kind of radiation that has both electric and magnetic fields and travels in waves.

Question 11

EMR Facts

Answer 11

• Electromagnetic radiation consists of energy traveling in the form of waves through space that radiate from energy sources.
• Einstein proposed that energy can behave as a particle or a wave.
• These energy particles are called Photons. These are a type of elementary particle that have energy and movement but do NOT have a mass or an electrical charge.
• All photons travel at the speed of light.

Question 12

The forms of EMR in the Electromagnetic Spectrum (in order)

Answer 12

1. Radio waves
2. Microwaves
3. Infrared radiation
4. Visible light
5. UV radiation
6. X-ray
7. Gamma ray

Question 13

Visible Light

Answer 13

Visible light can be used to model all types of electromagnetic radiation.

• It is invisible as it travels (visible light must interact with matter to become visible)
• It involves the transfer of energy from one place to another.
• It travels through empty space at the speed of light (3.00 x 10*8 m/s)
• It can travel through empty space.
• It has both electrical and magnetic properties.

Question 14

The Wave Model of Light

Answer 14

The wave model of light is part of a theory that explains that light has wave-like properties. In the 1800s, Thomas Young’s experiment showed that light spreads out into a series of lines when it passes through two marrow slits. This pattern of lines could only be explained if light has wave-like properties.

Question 15

The Ray Model of Light

Answer 15

The ray model of light is the idea that light travels in a straight line.
Light moves in a straight line and cannot bend around objects.
It is used to model and describe how light behaves.
Ray diagrams can be used to predict size, location, and shape of shadows.

Question 16

The Particle Model of Light

Answer 16

The particle model of light explains that light has particle-like properties.
The photoelectric effect cannot be explained by the models we mentioned before.
The photoelectric effect:
- Different colors of light shine onto a certain metal.
- Electrons are never given off when energy from red light hits the metal. (Violet light has the most energy, and red has the least)
- Electrons are always given off when energy from blue light hits the metal.
- If light is only a wave, any wavelength of light could carry enough energy to cause the release of electrons.
- Einstein suggested that light interatcs with matter as packets or distinct particles of energy (photons)
- Each photon must carry an exact amount of energy that is enough to make the metal give off electrons. They must carry more energy as the frequency of electromagnetic radiation increases and the wavelength decreases.

Question 17

Refraction General Facts

Answer 17

Refraction occurs because light travels at different speeds in different media (plural of medium)
Angle of refraction: The angle measure between the incident light ray and the normal.
The degree of the angle of refraction is related to the density of the medium.
Light slows down as it travels from less dense to more dense medium, and bends toward the normal.
Light speeds up as it travels from more dense to less dense medium, and bends away from the normal.

Question 18

Reflection vs. Refraction

Answer 18

Definition of reflection: Light bounces off a surface.
Definition of angle: The angle of reflection is equal to the angle of incidence. It is the angle between the reflected ray and the normal.
Definition of refraction: Light bends.
Definition of angle: The degree of angle of refraction is related to the density of the medium. It is the angle between the incident light ray and the normal.

Question 19

Rainbows & Mirages

Answer 19

Rainbows: When sunlight hits a rain droplet, some of the light is reflected. The electromagnetic spectrum is made of light with many different wavelengths, and each is reflected at a different angle. Thus, spectrum is separated, producing a rainbow. Red has the longest wavelength of visible light, about 650 nanometers.
Mirages: Mirages happen when the ground is very hot and the air is cool. The hot ground warms a layer of air just above the ground. When the light moves through the cold air and into the layer of hot air it is refracted (bent). A layer of very warm air near the ground refracts the light from the sky nearly into a U-shaped bend.