SS Two
Physics
Third Term
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Define Wave: A wave can be defined as a disturbance (or oscillation) that travels through a medium, transporting energy from one location (its source) to another location without transporting matter.
More Explanation About Wave
A wave is a physical phenomenon characterised by its frequency (f), wavelength (λ) and amplitude (A).
Production of Mechanical Waves
All objects in motion produce some amount of waves. This is caused by vibration of the particles
of the object when it is set in motion. Examples are (i) Waves on a string (ii) Waves in slinky spring (iii) Water waves in ripple tank.
Types of Waves
Transverse Waves: Transverse waves are waves that travel perpendicularly to the direction of the vibrations producing them (Fig 1, top diagram).
Longitudinal waves: These are waves that travel parallel to the direction of the vibrations producing them (Fig 1, bottom diagram).
Watch this video Wave Speed of Transverse Wave on a Stretched String. Then write out the equations from the video in your note.
Reflection involves a change in direction of waves when they bounce off a barrier. Refraction of waves involves a change in both the direction and speed of waves as they pass from one medium to another. But diffraction involves a change in direction of waves as they pass through an opening or around a barrier in their path. Water waves are common examples because they have the ability to travel around corners, around obstacles and through openings. Watch the video on
Wave Diffraction
In other words, diffraction is the bending of waves as they move around an obstacle or through an opening. The opening is also called a slit.
If the obstacle is much bigger than the wavelength, there is very small diffraction. If we make the obstacle or slit the size of the wavelength or smaller, we get true diffraction. Therefore, wave diffraction occurs when we have either an obstacle or we have some kind of an opening. Light waves, water waves and sound waves all undergo diffraction.
Diffraction of water waves is observed in a harbor as waves bend around small boats and are found to disturb the water behind them.
Questions (1) Define diffraction (2) (i) State two types of diffraction. What size of obstacle or slit that produces each of the diffractions stated in (i)
There are two basic laws of reflection. These are stated as follows
- The light ray, the reflected light ray and the normal at the point of incidence all lie in the same plane.
- The angle of the incident light ray (i) is equal to the angle of the reflected light ray (r). The second law most commonly applied in calculations. Watch the video on What is the Law of Reflection?
The incident rays represent the light that initially strike the object and the reflected rays denote the light that bounces off the object after striking it. The angle of incidence is the angle that the incident ray makes with the normal and the angle of reflection is the angle that the reflected ray makes with the normal
Last week, refraction through glass prison was discussed. Watch the following video to keep memory fresh Refraction of light through a prism.
Define a lens: A lens is any transparent object with two faces, with at least one of the faces curved. There are two broad categories of lenses, concave and convex lenses. The latter is often modeled to have approximately the same shape as the human eye. Each of the broad categories of lenses is further divided into three. The convex lens include biconvex, plano-convex and meniscus convex while the concave lens consists of biconcave, plano-concave and meniscus concave. These are illustrated in the diagram below.
Properties of lenses: The properties of a lens include optical centre, principal axis, principal focus, focal length and power of the lens.
The image formed by a single lens can be located and sized with three principal rays. The three rays usually leave from one point on an “object”. The “three principal rays” which are used for visualizing the image location and size are:
- Light rays from the object that travel parallel to the principal axis (or optical axis) AB, are refracted off the lens through the principal focus (or focal point), F.
- The reverse statement of no. 1 leads to statement 2. Light rays from the object that travel through the principal focus, F, are refracted parallel to the principal axis,
- Light rays that travel through the optical centre, C, are refracted through the same optical centre. That is, they are un-deviated.
Where these three rays converge (or seem to converge), is the corresponding point on the image.
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