Mcat Physics: Optics

Front 1

What is light?

Back 1

Electromagnetic waves with wavelengths that are within or near the visually detectable range (typically 400 to 700nm).

Front 2

1. reflected beam
2. refracted beam
3. transparent

Back 2

1. When a narrow beam of incoming light (the incident beam), angled downward from the left and traveling through air, encounters a plane (flat) glass surface, part of the light seems to bounce off the smooth glass surface forming a smooth glass reflected beam. The rest of the light travels through the surface and into the glass, forming a refracted beam directed downward to the right. Because the surface of the glass is smooth, the refracted light forms a beam rather than being scattered in many directions and this is said to be transparent.

Front 3

What is refraction?

Back 3

The passage of light from one homogeneous surface to another with a smooth surface (for example from air to glass) is called refraction and the light is said to be refracted.

Front 4

What happens if the incident beam of light is perpendicular to the surface?

Back 4

The direction of light remains unchanged.

Front 5

What is "The normal"?

Back 5

Each ray (the incident ray, a reflected ray and a refracted ray) is oriented with respect to a line, called the normal, that is perpendicular to the surface at the point of reflection and refraction.

Front 6

Law of Reflection

Back 6

A reflected ray lies in the plane of incidence and has an angle of reflection equal to the angle of incidence. Θ'=Θ

Front 7

Law of Refraction (or Snell's Law)

Back 7

A refracted ray lies in the plane of incidence and has an angle of refraction Θ2 that is related to the angle of incidence Θ1 by: n2sinΘ2=n1sinΘ1.
n1 and n2 are a dimensionless constant, called the index of refraction, that is associated with a medium involved in the refraction.
For vacuum n=1, for air n is very close to 1.0.
If we know Θ1 we can find Θ2 by rearranging the previous equation sinΘ2=n1/n2sinΘ1

Front 8

What are the three basic rules of the relative values of n2 and n1?

Back 8

1. If n2=n1, then Θ2 is equal to Θ1.(in this case, refraction does not bend the light beam, which continues in the undeflected direction.
2. If n2>n1, then Θ2<Θ1. (In this case, refraction bends the light beam away from the undeflected direction and toward the normal.
3. If n2<n1, then Θ2>Θ1. (In this case, refraction bends the light beam away from the undeflected direction and away from the normal.

Front 9

What is Chromatic Dispersion?

Back 9

The index of refraction n encountered by light in any medium except a vacuum depends on the wavelength of the light. The dependence of n on wavelength implies that when a light beam consists of rays of different wavelengths, the rays will be refracted at different angles by a surface; that is, the light will be spread out by the refraction. This spread of light is called chromatic dispersion.

Front 10

What is Critical Angle and Total Internal Reflection?

Back 10

When the angle of incidence increases then the angle of refraction increases until it becomes 90 degrees, which means that the refracted ray points directly along the interface (surface). The angle of incidence that gives this situation is called the critical angle Θc and we find it as follows:
n1sinΘc=n2sin90 => Θc= sin^-1(n2/n1).
For angles of incidence larger than Θc, there is no refracted ray and all the light is reflected, this effect is called total internal reflection.

Front 11

When total internal reflection cannot occur?

Back 11

Because the sine of an angle cannot exceed unity, n2 cannot exceed n1 in the equation (Θc=sin^-1(n2/n1). This restriction tells us that total internal reflection cannot occur when the incident light is in the medium of lower index of refraction.

Front 12

What is the Brewster's Law/Brewster's angle?

Back 12

When the light is incident at a particular incident angle, called the Brewster angle ΘB, the reflected light has only perpendicular components. Experiementally we can find out that the reflected and refracted rays are perpendicular to each other. Because the refracted ray is reflected at the angle ΘB and the refracted ray is at an angle Θ2=Θr, we have ΘB+Θr=90, so: ΘB= tan^-1 (n2/n1)

Front 13

Virtual Image?

Back 13

If the light rays have been reflected toward you from a standard flat mirror, the object appears to be behind the mirror because the rays you intercept come from that direction. This type of image is virtual image.

Front 14

Real image?

Back 14

A real image can be formed on a surface, such as a card of a movie screen.

Front 15

What is the distance between the image and the object in a plane mirror?

Back 15

i=-o The image is as far behind the mirror as the object is in front of it.