Comment No. 772089094570334543

Sorry po pala kung ngayon lang ako nakapagpost ulit, sorry po sir!!!

Comment No. 7360029347238650954

Hhhhhhhaaaaaaaaaaiiiiiiii!!!! at last, the periodic exams were already done, especially in Physics test. Oh my God I'm so irritated when I am about to struggle my test in Physics because of too much heat thats why I got a low score. But then I did all my best just to make my exam. Hhhhhmmmmm!!! for sir Mendoza: "hai naku sir tatagalugin ko na lang po ito, lahat po ng mga items sa test ay puro solving, alam nyo po ba? lampas na ng kalahating oras eh number eight pa lang ako. hehehe.

Comment No. 8600283654998034354

Hi there again. Well I got a bad score last time when we had our second long test in Physics III. It is a hard one because it like an entrance exam in UP even though I didn't try to take the test there. Atleast I have tried already how hard is that coming test in my life"huhu" even though it is too hard. I think Sir Mendoza should know that we are giving much attention to our Physics class even though Chemistry is our main science subject in this year because Physics is the hardest field of Science and our teacher make us suffer if I know "hhmmmmmmm". So I must take care of my grades for me to pass his subject, and I think I can handle this subject by focusing on the lessons first before I proceed to advanced lessons. And I must make my scores high especially this coming Periodic exam in Physics "Oh My God, I am afraid,,,shivering". To sir Mendoza, "hhhhmmmm, hi there and take care".

Cases of Lenses

If the lens is biconvex or plano-convex, a collimated or parallel beam of light travelling parallel to the lens axis and passing through the lens will be converged (or focused) to a spot on the axis, at a certain distance behind the lens (known as the focal length). In this case, the lens is called a positive or converging lens.

If the lens is biconcave or plano-concave, a collimated beam of light passing through the lens is diverged (spread); the lens is thus called a negative or diverging lens. The beam after passing through the lens appears to be emanating from a particular point on the axis in front of the lens; the distance from this point to the lens is also known as the focal length, although it is negative with respect to the focal length of a converging lens.

If the lens is convex-concave (a meniscus lens), whether it is converging or diverging depends on the relative curvatures of the two surfaces. If the curvatures are equal, then the beam is neither converged nor diverged.

Lens
A curved piece of ground and polished or molded material, usually glass, used for the refraction of light. Its two surfaces have the same axis. Usually this is an axis of rotation symmetry for both surfaces; however, one or both of the surfaces can be toric, cylindrical, or a general surface with double symmetry (see illustration). The intersection points of the symmetry axis with the two surfaces are called the front and back vertices and their separation is called the thickness of the lens. There are three lens types, namely, compound, single, and cemented. A group of lenses used together is a lens system. Such systems may be divided into four classes: telescopes, oculars (eyepieces), photographic objectives, and enlarging lenses.
a) Biconvex. (b) Plano-convex. (c) Positive meniscus. (d) Biconcave. (e) Plano-concave. (f) Negative meniscus. (After F. A. Jenkins and H. E. White, Fundamentals of Optics, 4th ed., McGraw-Hill, 1976)" src="http://content.answers.com/main/content/img/McGrawHill/Encyclopedia/images/CE377000FG0010.gif">Common lenses. (a) Biconvex. (b) Plano-convex. (c) Positive meniscus. (d) Biconcave. (e) Plano-concave. (f) Negative meniscus. (After F. A. Jenkins and H. E. White, Fundamentals of Optics, 4th ed., McGraw-Hill, 1976)
Lens types
A compound lens is a combination of two or more lenses in which the second surface of one lens has the same radius as the first surface of the following lens and the two lenses are cemented together. Compound lenses are used instead of single lenses for color correction, or to introduce a surface which has no effect on the aperture rays but large effects on the principal rays, or vice versa. Sometimes the term compound lens is applied to any optical system consisting of more than one element, even when they are not in contact.
The diameter of a simple lens is called the linear aperture, and the ratio of this aperture to the focal length is called the relative aperture. This latter quantity is more often specified by its reciprocal, called the f-number. Thus, if the focal length is 50 mm and the linear aperture 25 mm, the relative aperture is 0.5 and the f-number is f/2. See also Focal length.
A compound lens made of two or more simple thin lenses cemented together is called a cemented lens.
Lens systems
A lens system consisting of two systems combined so that the back focal point of the first (the objective) coincides with the front focal point of the second (the ocular) is called a telescope. Parallel entering rays leave the system as parallel rays. The magnification is equal to the ratio of the focal length of the first system to that of the second.
A photographic objective images a distant object onto a photographic plate or film. The amount of light reaching the light-sensitive layer depends on the aperture of the optical system, which is equivalent to the ratio of the lens diameter to the focal length. The larger the aperture (the smaller the f-number), the less adequate may be the scene luminance required to expose the film. Therefore, if pictures of objects in dim light are desired, the f-number must be small. On the other hand, for a lens of given focal length, the depth of field isinversely proportional to the aperture.
In general, photographic objectives with large fields have small apertures; those with larg apertures have small fields.
The basic type of enlarger lens is a holosymmetric system consisting of two systems of which one is symmetrical with the first system except that all the data are multiplied by the enlarging factor m. When the object is in the focus of the first system, the combination is free from all lateral errors even before correction. A magnifier in optics is a lens that enables an object to be viewed so that it appears larger than its natural size. The magnifying power is usually given as equal to one-quarter of the power of the lens expressed in diopters.

Reflection

Change in the direction of propagation of a wave that strikes a boundary between different media through which it cannot pass. When a wave strikes such a boundary it bounces back, or is reflected, just as a ball bounces off the floor. The angle of incidence is the angle between the path of the wave and a line perpendicular to the boundary. The angle of reflection is the angle between the same line and the path of the reflected wave. All reflected waves obey the law of reflection, which states that the angle of reflection is equal to the angle of incidence. The reflectivity of a material is the fraction of energy of the oncoming wave that is reflected by it.

Refraction

Change in direction of a wave as it leaves one medium and enters another. Waves, such as sound and light waves, travel at different speeds in different media. When a wave enters a new medium at an angle of less than 90°, the change in speed occurs sooner on one side of the wave than on the other, causing the wave to bend, or refract. When water waves approach shallower water at an angle, they bend and become parallel to the shore. Refraction explains the apparent bending of a pencil when it is partly immersed in water and viewed from above the surface. It also causes the optical illusion of the mirage.

Diffraction

The bending of light, or other waves, into the region of the geometrical shadow of an obstacle. More exactly, diffraction refers to any redistribution in space of the intensity of waves that results from the presence of an object that causes variations of either the amplitude or phase of the waves. Most diffraction gratings cause a periodic modulation of the phase across the wavefront rather than a modulation of the amplitude. Although diffraction is an effect exhibited by all types of wave motion, this article will deal only with electromagnetic waves, especially those of visible light. For discussion of the phenomenon as encountered in other types of waves.

Rectilinear Propagation

Rectilinear propagation is a wave property which states that waves propagate (move or spread out) in straight lines. This property applies to both transverse and longitudinal waves. Even though a wave front may be bent (the waves created by a rock hitting a pond) the individual waves are moving in straight lines.

Interference

When two or more waves interact and combine, they interfere with one another. But interference is not necessarily bad: waves may interfere constructively, resulting in a wave larger than the original waves. Or, they may interfere destructively, combining in such a way that they form a wave smaller than the original ones. Even so, destructive interference may have positive effects: without the application of destructive interference to the muffler on an automobile exhaust system, for instance, noise pollution from cars would be far worse than it is. Other examples of interference, both constructive and destructive, can be found wherever there are waves: in water, in sound, in light.

Sound

This article is about acoustic waves. For other uses, see Sound (disambiguation).
Sound is a disturbance of mechanical energy that propagates through matter as a wave. Sound is characterized by the properties of waves, which are frequency, wavelength, period, amplitude, and speed.

Humans perceive sound by the sense of hearing. By sound, we commonly mean the vibrations that travel through air and can be heard by humans. However, scientists and engineers use a wider definition of sound that includes low and high frequency vibrations in air that cannot be heard by humans, and vibrations that travel through all forms of matter, gases, liquids, solids, and plasmas.

The matter that supports the sound is called the medium. Sound propagates as waves of alternating pressure, causing local regions of compression and rarefaction. Particles in the medium are displaced by the wave and oscillate. The scientific study of sound is called acoustics.

Noise is often used to refer to an unwanted sound. In science and engineering, noise is an undesirable component that obscures a wanted signal.


Perception of Sound

A schematic representation of hearing. (Blue: sound waves. Red: eardrum. Yellow: cochlea. Green: auditory receptor cells. Purple: frequency spectrum of hearing response. Orange: nerve impulse)Sound is perceived through the sense of hearing. Humans and many animals use their ears to hear sound, but loud sounds and low-frequency sounds can be perceived by other parts of the body through the sense of touch as vibrations. Sounds are used in several ways, notably for communication through speech and music. They can also be used to acquire information about properties of the surrounding environment such as spatial characteristics and presence of other animals or objects. For example, bats use echolocation, ships and submarines use sonar and humans can determine spatial information by the way in which they perceive sounds.

Humans can generally hear sounds with frequencies between 20 Hz and 20 kHz (the audio range) although this range varies significantly with age, occupational hearing damage, and gender; the majority of people can no longer hear 20,000 Hz by the time they are teenagers, and progressively lose the ability to hear higher frequencies as they get older. Most human speech communication takes place between 200 and 8,000 Hz and the human ear is most sensitive to frequencies around 1000-3,500 Hz. Sound above the hearing range is known as ultrasound, and that below the hearing range as infrasound.

The amplitude of a sound wave is specified in terms of its pressure. The human ear can detect sounds with a very wide range of amplitudes and so a logarithmic decibel amplitude scale is used. The quietest sounds that humans can hear have an amplitude of approximately 20 µPa (micropascals) or a sound pressure level (SPL) of 0 dB re 20 µPa (often incorrectly abbreviated as 0 dB SPL). Prolonged exposure to a sound pressure level exceeding 85 dB can permanently damage the ear, resulting in tinnitus and hearing impairment. Sound levels in excess of 130 dB are more than the human ear can safely withstand and can result in serious pain and permanent damage. At very high amplitudes, sound waves exhibit nonlinear effects, including shock.

The way in which sound travels or propagates is difficult to imagine, as sound appears to humans as invisible. Imagine a long tube exposed to air whereby sound travels longitudinally through it. The air acts like a Slinky spring in this tube. As sound is generated at one end, the wave will begin to travel down through the air in the tube, (watching an earth worm move by pulsating its long body on the top of the ground helps to visualize this same phenomenon). The length of pulse cycle will determine the sound wave length. Low bass sounds will have large pulse lengths, in the order of 10-50 feet long, where high treble sounds will have pulse lengths as small as 1/2 an inch.


Speed of Sound

Main article: Speed of sound
The speed at which sound travels depends on the medium through which the waves are passing, and is often quoted as a fundamental property of the material. In general, the speed of sound is proportional to the square root of the ratio of the elastic modulus (stiffness) of the medium and its density. Those physical properties and the speed of sound change with ambient conditions. For example, the speed of sound in air and other gases depends on temperature. In air, the speed of sound is approximately 344 m/s, in water 1500 m/s and in a bar of steel 5000 m/s. The speed of sound is also slightly sensitive (to second order) to the sound amplitude, resulting in nonlinear propagation effects, such as the weak production of harmonics and the mixing of tones. (see parametric array).


Sound Pressure

Main article: Sound pressure
Sound pressure is the pressure deviation from the local ambient pressure caused by a sound wave. Sound pressure can be measured using a microphone in air and a hydrophone in water. The SI unit for sound pressure is the pascal (symbol: Pa). The instantaneous sound pressure is the deviation from the local ambient pressure caused by a sound wave at a given location and given instant in time. The effective sound pressure is the root mean square of the instantaneous sound pressure averaged over a given interval of time. In a soundwave, the complementary variable to sound pressure is the acoustic particle velocity. For small amplitudes, sound pressure and particle velocity are linearly related and their ratio is the acoustic impedance. The acoustic impedance depends on both the characteristics of the wave and the medium. The local instantaneous sound intensity is the product of the sound pressure and the acoustic particle velocity and is, therefore, a vector quantity in time.

The loudest sound ever historically reported was the 1883 volcanic eruption of Krakatoa whereby sound levels reached levels of 180 dBSPL 100 miles (160 km) away.

Sound Pressure Level

As the human ear can detect sounds with a very wide range of amplitudes, sound pressure is often measured as a level on a logarithmic decibel scale.

The sound pressure level (SPL) or Lp is defined as


where p is the root-mean-square sound pressure and p0 is a reference sound pressure. (When using sound pressure levels, it may be important to quote the reference sound pressure used.) Commonly used reference sound pressures, defined in the standard ANSI S1.1-1994, are 20 µPa in air and 1 µPa in water.
Since the human ear does not have a flat spectral response, sound pressure levels are often frequency weighted so that the measured level will match perceived levels more closely. The International Electrotechnical Commission (IEC) has defined several weighting schemes. A-weighting attempts to match the response of the human ear to noise and A-weighted sound pressure levels are labeled dBA. C-weighting is used to measure peak levels.


Examples of sound pressure and sound pressure levels


Source of sound sound pressure sound pressure level
pascal dB re 20 µPa
threshold of pain 100 134
hearing damage during short-term effect 20 approx. 120
jet engine, 100 m distant 6–200 110–140
jack hammer, 1 m distant / discotheque 2 approx. 100
hearing damage during long-term effect 0.6 approx. 90
major road, 10 m distant 0.2–0.6 80–90
passenger car, 10 m distant 0.02–0.2 60–80
TV set at home level, 1 m distant 0.02 ca. 60
normal talking, 1 m distant 0.002–0.02 40–60
very calm room 0.0002–0.0006 20–30
leaves noise, calm breathing 0.00006 10
auditory threshold at 2 kHz 0.00002 0


Equipment for dealing with sound
Equipment for generating or using sound includes musical instruments, hearing aids, sonar systems and sound reproduction and broadcasting equipment. Many of these use electro-acoustic transducers such as microphones and loudspeakers.

Intensity

In physics, intensity is a measure of the time-averaged energy flux. To find the intensity, take the energy density (that is, the energy per unit volume) and multiply it by the velocity at which the energy is moving. The resulting vector has the units of power divided by area (i.e. watt/m²). It is possible to define the intensity of the water coming from a garden sprinkler, but intensity is used most frequently with waves (i.e. sound or light).

In physics, the word "intensity" is not synonymous with "strength", "amplitude", or "level", as it sometimes is in colloquial speech. For example, "the intensity of pressure" is meaningless, since the parameters of those variables do not match.

If a point source is radiating energy in three dimensions and there is no energy lost to the medium, then the intensity decreases in proportion to distance from the object squared. This is due to physics and geometry. Physically, conservation of energy applies. The consequence of this is that the net power coming from the source must be constant, thus:


where P is the net power radiated, I is the intensity as a function of position, and dA is a differential element of a closed surface that contains the source. That P is a constant. If the source is radiating uniformly, i.e. the same in all directions, and we take A to be a sphere centered on the source (so that I will be constant on its surface), the equation becomes:


where I is the intensity at the surface of the sphere, and r is the radius of the sphere. (4πr2 is the expression for the surface area of a sphere). Solving for I, we get:


If the medium is damped, then the intensity drops off more quickly than the above equation suggests.

Anything that can carry energy can have an intensity associated with it. For an electromagnetic wave, if E is the complex amplitude of the electric field, then the power carried by the wave is given by

,
and the intensity is obtained multiplying this expression by the velocity of the wave, c / n:

,
where n is the refractive index, c is the speed of light in vacuum and ε0 is the electric permittivity in vacuum.

Photometry and Radiometry

In photometry and radiometry, intensity has a different meaning: it is the luminous or radiant power per unit solid angle. This can cause confusion in optics, where intensity can mean any of radiant intensity, luminous intensity or irradiance, depending on the background of the person using the term. Radiance is also sometimes called intensity, especially by astronomers and astrophysicists.

Comment #83578347956485830

Hi! there, here I am again. Well as of now I am happy coz I passed the tests that we have took in our Physics Class but I am not acting as a person who makes some easy easy matters then I should take care of my scores as I am about to struggle different lessons in Physics. Maybe I should balance my scores, I mean I should not take them for granted.

Steps in Component Method

1. Draw each vector and show its components.
2. Determine the magnitude and direction of the components by using the trigonometric functions.
3. Find the sum of the x-components.
4. Find the sum of the y-components.
5. the answers obtained in steps 3 and 4 are the x and y components of the resultant vector. Use these components to find the magnitude and the direction of the resultant vector, using the Pythagorean Theorem and the Trigonometric Functions.
6. Check your answer by comparing it with the result obtained in Graphical Method (optional).
   

Steps in Graphical Method

1. First, choose an appropriate scale and coordinate system for the given vectors.
2. Draw the first vector starting from the origin of the coordinate system. Draw the second vector starting from the head of the first vector. Proceed to draw the remaining vectors starting from the head of the most recent vector drawn. All vectors must be connected in series, head-to-tail fashion.
3. Draw a new vector connecting the tail of the first to the head of the last vector drawn. the new vector is the resultant of the given vectors.
   

Resultant Vector

Scalar Quantities can be addedand subtracted like ordinary numbers provided the scalars have the same units. For vectors, the sum depends on the direction of the vectors. The sum of two or more vectors is represented by a single vector called the Resultant.

Common Prefixes of the Metric System


Prefix, Symbol, Factor

milli, m, 0.001
centi, c, 0.01
deci, d, 0.1
deka, da, 10
hecto, h, 100
kilo, k, 1000
mega, m, 1000000
giga, g, 1000000000

Comment no. 660398375908374

I'm happy in my Physics class because when we are about to take a test for the second time around, sir Mendoza did help me to answer my test, i asked him about how to solve for the direction of the vector that is needed to that problem and he helped me, im so happy of that because i got a high score in that test because he explained to me how to do it. hehe!

About Me...

I'm Jayvee D. Tabal of III-Ptolemy, Manila Science High School, 14 yrs old

I'm part of the Manila Science High School Chorale coz' my favorite hobby and my talent is singing

Mathematics and Chemistry are my favorite subjects, I also like Physics but it is quite hard

I am more enhanced in Philippine language compare to English so I can say to myself that I am a Great Filipino Citizen and I am proud of it

I like teachers who are friendly to students and considerate like Mr. Mendoza and also with a right outlook in life

Comment No. 3486

When i saw before Mr. Mendoza, i taught he is a simple one but then i finally found out that sir is scary because he is very strict and miticulous. Even if he has that trait, he is a friendly and considerate. I hope it will not last so that me and my classmates will not be scared with him.

Hi!!!

Welcome!!!

This is my Blog in Physics: A Project

UNDER CONSTRUCTION!!!