Optics
Ø Light usually travels in straight lines. (This is called rectilinear propagation)
Ø The direction that the light is travelling is represented by a ray.
Ø A beam of light can be represented by a number of rays.
Ø The direction that the light is travelling is represented by a ray.
Ø A beam of light can be represented by a number of rays.
Reflection by plane mirrors – Laws of reflection
1. The incident ray, the reflected ray and the normal ray are all in the same plane.
2. The angle of incidence is equal to the angle of reflection.
Real or virtual: A real image is an image that can be touched and can be produced on a screen while a virtual image cannot be touched or produced on a screen.
Properties of images in plane images:
- The image is as far behind as the object is in front of the mirror and the line joining a point from the object to a corresponding point on the image . are at right angles to the mirror.
- The image is the same size as the object.
- The image is virtual.
- The image is laterally inverted (i.e. the left and right are opposite)
- The image is erect.
1. The incident ray, the reflected ray and the normal ray are all in the same plane.
2. The angle of incidence is equal to the angle of reflection.
Real or virtual: A real image is an image that can be touched and can be produced on a screen while a virtual image cannot be touched or produced on a screen.
Properties of images in plane images:
- The image is as far behind as the object is in front of the mirror and the line joining a point from the object to a corresponding point on the image . are at right angles to the mirror.
- The image is the same size as the object.
- The image is virtual.
- The image is laterally inverted (i.e. the left and right are opposite)
- The image is erect.
Refraction of light:
Ø Refraction is the bending of light from one medium to another.
Ø Anything which light can pass through is a medium.
Ø Refraction happens because there is a change in speed.
As the light is passing through medium 1 which is air it is moving at one speed but when the light then passes from air to glass (medium 2) the light is refracted towards the normal.
Note: the greater the refractive index of a medium the more the ray would bend when it enters it from air.
Laws of refraction of light:
1. The incident ray, the refracted ray and the normal lie at the same plane at the point of incidence.
2. The ration of the ‘Sin’ of the angle of incidence is equal to the ‘Sin’ of the angle of reflection.
Ø Refraction is the bending of light from one medium to another.
Ø Anything which light can pass through is a medium.
Ø Refraction happens because there is a change in speed.
As the light is passing through medium 1 which is air it is moving at one speed but when the light then passes from air to glass (medium 2) the light is refracted towards the normal.
Note: the greater the refractive index of a medium the more the ray would bend when it enters it from air.
Laws of refraction of light:
1. The incident ray, the refracted ray and the normal lie at the same plane at the point of incidence.
2. The ration of the ‘Sin’ of the angle of incidence is equal to the ‘Sin’ of the angle of reflection.
Snell’s Law:
Note: The Refractive index is equal to the velocity of light in air divided by the velocity of light in medium.
Real and apparent depth:
Ø If you look at a fish in the water it appears closer to the surface then it actually is.
Ø The refractive index here is equal to the real depth divided by the apparent depth.
Note: The Refractive index is equal to the velocity of light in air divided by the velocity of light in medium.
Real and apparent depth:
Ø If you look at a fish in the water it appears closer to the surface then it actually is.
Ø The refractive index here is equal to the real depth divided by the apparent depth.
Total Internal Reflection:
1. For a small angle of incidence the bright refracted ray is produced and also a weak internally reflected ray.
2. When increasing the angle of incidence and reaching a certain point the critical angle is found and the refracted ray gazes the glass.
3. When the critical angle is exceeded the reflected ray becomes bright and the refracted ray disappears. This is called total internal reflection.
1. For a small angle of incidence the bright refracted ray is produced and also a weak internally reflected ray.
2. When increasing the angle of incidence and reaching a certain point the critical angle is found and the refracted ray gazes the glass.
3. When the critical angle is exceeded the reflected ray becomes bright and the refracted ray disappears. This is called total internal reflection.
Measuring the critical angle of a glass:
Total Internal Reflection
Ø Total internal reflection only takes place when light is in the denser medium and approaching the less dense medium, and the angle of incidence is greater than the critical angle.
Refraction in Prisms
Ø When light passes through a glass prism it undergoes refraction at the face at which it leaves the prism as seen in the diagram. The deflection (D) of the path of the ray of light is referred to as deviation.
Ø Total internal reflection only takes place when light is in the denser medium and approaching the less dense medium, and the angle of incidence is greater than the critical angle.
Refraction in Prisms
Ø When light passes through a glass prism it undergoes refraction at the face at which it leaves the prism as seen in the diagram. The deflection (D) of the path of the ray of light is referred to as deviation.
Totally reflecting Prisms
Lenses
Ø There are two types of lenses, converging and diverging lenses.
Ray diagrams
Ø Information about the images formed by a lens can be obtained by drawing two of the following:
1. A ray parallel to the principle axis which is refracted through the principle focus.
2. A ray through the principle focus which is refracted parallel to the principal axis.
3. A ray through the optical center which is undeviated.
Lenses
Ø There are two types of lenses, converging and diverging lenses.
Ray diagrams
Ø Information about the images formed by a lens can be obtained by drawing two of the following:
1. A ray parallel to the principle axis which is refracted through the principle focus.
2. A ray through the principle focus which is refracted parallel to the principal axis.
3. A ray through the optical center which is undeviated.
References:
- Mr M. Muscat Ordinary Level Physics Notes.
- www.wikipedia.com