Chapter 5: Geometrical Optics Flashcards
What is a light ray?
A light ray is a line, straight or curved, that is perpendicular to the wavefront; it’s tangent is collinear with the wave vector
When light interacts with an object or medium, what can happen?
Light can be reflected, absorbed or transmitted
Are light rays real?
No, light rays are not real. Light rays are used to indicate the direction in which light travels. In geometrical optics, we represent light rays as arrows, depicting the direction of propagation of wavefronts.
How does reflection occur?
Reflection occurs when an incident ray (incoming light ray) bounces off a surface.
What is a reflected ray?
A reflected ray is a light ray moving away from the surface
How are the angles that light rays move at measured and explain?
These angles are measured with respect to the normal surface. The normal is an imaginary line perpendicular to the surface. The angle of incidence, Theta i, is measured between the incident ray and the surface normal. The angle of reflection, theta r, is measured the reflected ray and the surface normal.
What is the plane of incidence?
The plane of incidence is the plane including the incident ray and the normal to the surface. The reflected ray also lies in the plane of incidence.
What is the law of reflection?
The angle of incidence is equal to the angle of reflection. Theta i = theta r. And the incident ray, reflected ray, and the normal, all lie in the same plane.
What is the simplest example in which the law of reflection would be depicted?
The simplest example of the law of reflection is if the angle of incidence is 0. In this case, the angle of reflection is also 0. You see this when you look straight into a mirror.
What is a parabolic reflector?
A parabolic reflector is a mirror or dish which has a parabolic shape
How do parabolic reflectors work?
There are two ways in which a parabolic reflector may be used. One way is to emit light and the other is to absorb light. An example of the former would be a car headlight in which a light bulb emits light that is reflected off the parabolic reflector into collimated beams. An example of the latter would be a telescope in which collimated incident rays are reflected into a focus to gather information and form an image of galaxies.
Why do you get hotter wearing a black t-shirt outside than if you had to wear a white one?
The hue, black, absorbs almost all light (vanta black is the blackest colour and yet it still doesn’t absorb all colour as you’re able to see it)and through absorbing this light, it heats up through the heat energy it has gained. On the contrary, white light reflects almost all light and, therefore, heat energy and will ergo keep you cooler than if you had to wear a black t-shirt
Define transparent objects
Transparent objects are objects through which light can be transmitted
Define opaque objects
Opaque objects are objects/items through which light cannot be transmitted.
What does the transmission of light depend on?
The transmission of light through an object depends on the wavelength of the light
What is the maximum speed at which light can travel through a vacuum?
299 792 485 m/s
What is a vacuum?
A vacuum is a region with no matter in it, not even air
What symbol do we use to represent the speed of light in a vacuum and what do we approximate it to?
We use C to represent the speed of light in a vacuum. We approximate it to 3x10^8 m/s
What is the speed of light?
The speed of light, C, is constant in a given medium and has a maximum speed in a vacuum of 2.99792485x10^8 m/s, but we approximate it to 3x10^8 m/s
What happens when light travels from one medium into another?
The speed of the light changes depending on which medium it is traveling into, but its frequency remains the same
What is refraction?
Refraction is the change in direction of a wave, usually light as light is, both, a particle and a wave, passing from one medium to another
How does refraction occur?
Refraction occurs when light travels from one medium into another and changes speed, but its frequency remains constant. Light will also change direction if it does travel into the new medium perpendicularly
Why does a straw in a glass filled halfway with water look bent when observed?
The light rays leaving the straw changes direction when moving from air to water. Your eyes trace the light rays backwards as straight lines as if it had not changed direction. As a result of this, you see the straw shallower than it actually is.
What is the refractive index?
The refractive index(symbol n) of a material is the ratio of the speed of light in a vaccine to its speed in the material and gives an indication of how difficult it is for light to get through a material.
n = c/v
Where n= refractive index(no unit)
C= the speed of light in a vacuum (3x10^8m/s)
v= the speed of light in a given medium (m/s)
Can the refractive index ever be less than 1?
No. Since the refractive index of a material is the ratio of the speed of light in a vacuum to its speed in a given material, for the refractive index to be less than one, the speed of light in a given material (v) would have to be faster than the speed of light in a vacuum, which is impossible as the maximum speed that light can travel at is the speed of light in a vacuum
What is optical density?
Optical density is a measure of the refracting power of a medium. In other words, the higher the optical density, the more light will be refracted or slowed down as it moves through a medium.
What is the relationship between optical density and the refractive density of a material?
There is a positive relationship between optical density and the refractive index of a material. If a material has a high refractive index, then it would have a high optical density
