Electric charge is a physical property of matter which causes it to experience a forcewhen near other electrically charged matter. Electric charge comes in two types, calledpositive and negative. Two positively charged substances, or objects, experience a mutual repulsive force, as do two negatively charged objects. Positively charged objects and negatively charged objects experience an attractive force. The SI unit of electric charge is the coulomb (C)
Charge is the fundamental property of a matter that exhibit electrostatic attraction or repulsion over other matter. Electric charge is a characteristic property of many subatomic particles. The charges of free-standing particles are integer multiples of the elementary chargee; we say that electric charge isquantized. Michael Faraday, in his electrolysis experiments, was the first to note the discrete nature of electric charge. Robert Millikan's oil-drop experiment demonstrated this fact directly, and measured the elementary charge.
positive electric charge
negative electric charge
Charge is the fundamental property of a matter that exhibit electrostatic attraction or repulsion over other .
In the classical electrodynamics, light is considered as electromagnetic wave, which is governed by the Maxwell Equations. When light falls on the material, the electrons in the material oscillate with the electric fields and emit electromagnetic waves. The reflected light is the combination of the incident wave and the remitted waves.
In case of dielectric (glass), the electric field of the light acts on the electrons in the glass, the moving electrons generate a field and become a new radiator. The refraction light in the glass is the combined of the forward radiation of the electrons and the incident light and; the backward radiation is the one we see reflected from the surface of transparent materials, this radiation comes from everywhere in the glass, but it turns out that the total effect is equivalent to a reflection from the surface.
In metals, the electrons with no binding energy are called free electrons. The density number of the free electrons is very large. When these electrons oscillate with the incident light, the phase differences between the radiation field of these electrons and the incident field are π, so the forward radiation will compensate the incident light at a skin depth, and backward radiation is just the reflected light.
In the quantum-mechanical interpretation, light waves incident on a material induce small oscillations of polarisation in the individual atoms, causing each atom to radiate a weak secondary wave (in all directions like a dipole antenna). All these waves add up to specular reflection and refraction. Light–matter interaction in terms of photons is a topic of quantum electrodynamics, and is described in detail by Richard Feynman in his popular book QED: The Strange Theory of Light and Matter.
Total internal reflection can occur when light travels between two media from the medium with the higher refractive index into the medium with the lower index of refraction. There is a critical incident angle at which Snell's law predicts the refracted angle will be 90 degrees. At incident angles greater than this critical angle, light can not be refracted into the medium with the lower refractive index. Hence all the light striking the surface must be reflected. We have total internal reflection. The critical angle is given by the formula: sin(theta critical)=(n2/n1), where n1 is the larger refractive index and n2 is the smaller.
Total internal reflection can only occur when light is trying to travel from a material with a high refractive index into one with a lower refractive index. It will not occur when traveling from a low refractive index to a higher refractive index. For example, light traveling from glass to air might experience total internal reflection, but light traveling from air to glass never will. The greater the difference in refractive index between the two materials, the more likely there will be total internal reflection.
Fiber optic cables use total internal reflection inside the optical fiber. The light enters the optical fiber, and every time it strikes the edge of the fiber it experiences total internal reflection. This way the light travels down the length of the optical fiber.
Binoculars and other optical instruments often use prisms to reflect light. The light enters the prism in such a way that it will strike the other side of the prism and be totally internally reflected. The prism can in this way act as a mirror.
Rainbows form when light enters raindrops. The light is totally internally reflected inside the raindrop before leaving. In addition the light of different colors is refracted at different angles to separate the colors in an effect called dispersion.
The brilliance of diamonds results from light entering the diamond and being totally internally reflected from the opposite side before exiting in approximately the original direction.
Human beings living on Earth are affected by gravity because about two-thirds of our daily activities are standing or sitting. Because of this great amounts of body fluids such as blood pool in the lower part of the body. The human body is equipped with various mechanisms to oppose gravity to maintain sufficient blood flow to the brain.
In micro gravity environment, the quantity and the distribution of body fluid alters since it is free of the gravitational effect. This is the known as "fluid shift." Symptoms caused by fluid shift are stuffy nose, headache, and puffy face.
2) Effects on bone
Bones are systems involved in maintaining posture. The adult human body has 1,000 to 1,200 grams of calcium and 400 to 500 grams of phosphorus. However, once gravitational stress is removed, bone calcium and phosphorus are excessively excreted in urine and faeces. It is seen that 3.2% of average bone loss occurred after nearly 10 days of weightlessness. The loss of calcium in urine may produce urinary stone, which might cause severe pain, the decrease of bone density will lead to bone fracture. Therefore, countermeasures are necessary.
One countermeasure proposed to prevent bone loss is onboard exercise mainly with thetreadmill and ergo meter.
3) Effects on muscle
The human body floats within the orbiting spacecraft. Therefore, astronauts can move around in spacecraft just by softly pushing against its wall. In a micro gravity environment, muscles rapidly weaken due to the lack of use.
4) Space motion sickness
A few minutes or a few hours after entering weightlessness, astronauts experience space motion sickness, which is characterized by headaches, malaise, nausea and vomiting. Sixty to seventy percent of the astronauts experience these symptoms.
5) Effect on hematologic and immunologic system
One significant alteration in the hematologic and immunologic system in micro gravity is the transformation of red blood cells, the main component of blood. Ninety percent of our normal red blood cells have a biconcave discoid shape (i.e.) a doughnut without a hole. In weightlessness, some red blood cells transform into "mulberry" or spherical shape. However, they are readily reversed even after long-term space mission.
6) Effects of space radiation
Space radiation exists in the space environment. On the Earth, the atmosphere and magnetic field provide a shield for humans, and prevent space radiation from penetrating to the Earth's surface. Due to the absence of such shielding in the space environment, astronauts are subjected to greater amounts of space radiation than they would receive on the Earth. Therefore, the space radiation may seriously affect the astronauts.
8th - Problem solving on graphical method of representing motion.
key points - area under the curve of Speed time graph gives you distance.
for finding the gradient of speed time graph should have a big triangle on the curve to find the acceleration from the graph.
9th - Dispersion from the prism
White light enters in the prism and split into 7 colors
where RED deviate least and the VIOLET deviate most
Thats why the red light is used to represent the danger sign.
The elastic collision An elastic collision is an encounter between two bodies in which the total kinetic energy of the two bodies after the encounter is equal to their total kinetic energy before the encounter. Elastic collisions occur only if there is no net conversion of kinetic energy into other forms.
In collisions of macroscopic bodies, some kinetic energy is turned into vibrational energy of the atoms, causing a heating effect, and the bodies are deformed.
The molecules of a gas or liquid rarely experience perfectly elastic collisionsbecause kinetic energy is exchanged between the molecules' translational motion and their internal degrees of freedom with each collision. At any one instant, half the collisions are – to a varying extent – inelastic (the pair possesses less kinetic energy after the collision than before), and half could be described as “super-elastic” (possessing more kinetic energy after the collision than before). Averaged across an entire sample, molecular collisions are elastic.
The amount of refraction of light at a boundary between two media depends on three things:
The nature of the media (embodied in a characteristic quantity called the index of refraction for a medium).
The angle of indidence for the light ray on the boundary.
The wavelength of light.
The dependence of refraction on the wavelength of light is called dispersion. This dependence has both positive and negative implications for astronomy. On the positive side, it is the basis for the prism and its ability to separate light according to wavelength; on the negative side, it is the source of chromatic aberration in optical devices (the failure of different wavelengths to focus at the same point).
FOR 8TH IGCSE
The shapes of the velocity vs. time graphs for these two basic types of motion - constant velocity motion and accelerated motion (i.e., changing velocity) - reveal an important principle. The principle is that the slope of the line on a velocity-time graph reveals useful information about the acceleration of the object. If the acceleration is zero, then the slope is zero (i.e., a horizontal line). If the acceleration is positive, then the slope is positive (i.e., an upward sloping line). If the acceleration is negative, then the slope is negative (i.e., a downward sloping line). This very principle can be extended to any conceivable motion. The slope of a velocity-time graph reveals information about an object's acceleration. But how can one tell whether the object is moving in the positive direction (i.e., positive velocity) or in the negative direction (i.e., negative velocity)? And how can one tell if the object is speeding up or slowing down?
