Shadow Power 24

Ultraviolet light produces reactions in the skin then visible light. Some of these reactions are beneficial and some are harmful. One of the major beneficial effects of UV light from the sun is the conversion of molecular products in the skin into vitamin D. Ultraviolet light from the sun affects the melanin in the skin to cause tanning. However, UV light can produce sunburn as well as tan skin. Solar UV light is also the major cause of skin cancer in humans. The eye cannot see ultraviolet light because it is absorbed before it reaches the retina. About half of the energy from the sun is in the IR region. The warmth we fell from the sun is mainly due to the IR component. The IR rays are not usually hazardous-even though the cornea and lens of the eye onto the retina focus them. Our eyes also cannot see IR light.

The walls of the heart consist of layers of muscle, wound several times around the atria and the ventricles in a complicated arrangement. The layers of muscle around the ventricles are thicker than those around the atria. The heart muscle pumps blood by its cyclic contractions and relaxation. The contracted phase of the heart is called systole, and the relaxed phase is called diastole. Each contraction begins in the walls of the atria, and this squeezes the blood from the atria into the ventricles; a moment later, the walls of the ventricle contract. Squeezing the blood out of the heart into the ventricles; a moment later, the walls of the ventricle contract, squeezing the blood out of the heart into the arteries. Since the walls of both atria contract jointly, and the walls of both ventricles also contract jointly, the right and the left pumps in the heart always operate in unison. The layers of muscle around the left ventricle are much thicker than those around the right ventricle. T

Each of the pumps in the heart has two chambers. The upper chamber is called the atrium, and the lower chambers the ventricle (“belly”). The atria accumulate the blood arriving at the heart and then inject it into the ventricles. The ventricles eject the blood from the heart into the arteries; they perform most of the work required for the pumping. Each pump has two flap valves. The right pump has the tricuspid valve (between the atrium and the ventricle) and the pulmonary valve (at the beginning of the pulmonary artery). The left pump has the mistral valve (between the atrium and the ventricle) and the aortic valve (at the beginning of the aorta). These flap valves operate passively; their leaflets bend open to permit the flow of blood in the forward direction; but they flip shut when there is an incipient flow in the backward direction. We can best understand the operation of the chambers and the valves of the heart by tracing the flow of a parcel of blood through the heart and aroun

An open-tube manometer is a device for the measurement of the the pressure of a fluid, such as that contained in the tank shown on the left. The tube contains mercury, or water, or oil. One side of the tube is in contact with the fluid in the tank; the other is in contact with the air. The fluid in the tank, therefore, presses down on one end of the mercury column and the air presses down on the other end. The difference h in the heights of the levels of mercury at the two ends gives the difference in the pressure at the two ends, P - Po = Pgh Hence, this kind of manometer indicates the amount of pressure in the tank in excess of the atmospheric pressure. This excess is called the overpressure, or gauge pressure. It is well to keep in mind that much of the pressure is over pressure. For instance, the pressure gauges used for automobile tires read overpressure.

Several simple instruments for the measurement of pressure make use of a column of liquid. A mercury barometer consisting of a tube of glass, about 1m long, closed at the upper end and open at the lower end. The tube is filled with mercury, except for a small empty space at the top. The bottom of the tube is immersed in an open bowl filled with mercury. The atmospheric pressure action on the exposed airfare of mercury in the bowl prevents the mercury from flowing out of the tube. At the level of the exposed surface, the pressure exerted by the column of mercury is ρgh where ρ = 1.36 × 104 kg/m3 is the density of mercury and h the height of the mercury column. For equilibrium, this pressure must match the atmospheric pressure - P0= ρhg This equation permits a simple determination of the atmospheric pressure from a measurement of the height of the mercury column. In view of the direct correspondence of the atmospheric pressure and the height of the mercury column, the pressure is often q

When a force is applied on a body, rather than moving in uniform velocity, its velocity might increase or decrease with time and in this case, either the value or direction can change or both can change. Again, acceleration is the rate of change of velocity with time. Because if a body moves in uniform velocity, then it won't have any acceleration without the change of velocity. Therefore, active force is the main reason for acceleration.

The human heart beats about 70 times per minute. Each beat begins with a contraction of the atria which is followed a moment later by the contraction of the muscle. The contractions of the heart muscle, like the contractions of other muscles, are triggered by electric signals. But in contrast to other muscles, where the electric signals travel along nerve fibers, the electric signals in heart muscle travel along the muscle fibers. These electric signals involve changes of the electric potential in and around the muscle fibers. The changes of the electric potential associated with the heartbeats are strongest in the immediate vicinity of the muscle fibers; but, with a sensitive detector, the changes in the potential can be measured at some distance from the heart, on the surface of the skin. The detector used to measure such changes of potential is called electrocardiograph; it is widely used by physicians to monitor the operation of the heart and to discover defects in the heart muscle

Let us have two metallic balls. One of them is strongly charged and the other one is electrically neutral. If we now join them with iron wire or by metallic substance, then the neutral metallic ball will gain charge. Now if we touch them all with a wooden stick or rubber, then the neutral ball still remains neutral or chargeless. So, a substance like iron or metallic balls are called electrical conductors and wooden stick or rubbers is called nonconductor or insulator . All metals are well electrical conductor s. Silicon and Carbons are called semiconductors . Semiconductors are in the middle category in sense of conductors and insulators. All conductors are used to make electrical instruments, medical equipments. In the medical and nursing practice, their applications are wide and common.

Particles that exert electric forces are said to have electric charge particles that do not exert electric forces are said to have no electric charge. Thus, electric charge is thought of as the source of electric force, just as mass is the source of gravitational force. Electrons and protons have an electric charge, but neutrons have no electric charge.  Since the electron-proton force, the electron-electron force, and the proton-proton force all have the same magnitudes (for a given distance), the strengths of the sources on electrons and protons are of equal magnitudes; that is, their electric charges are of equal magnitudes. For the mathematical formulation of the law of electric force, we assign a positive charge to the proton and a negative charge (of equal magnitude) to the electron. We designate these charges of the proton and the electron by +e and -e, respectively Table summarizes these values of the charges. Table: Electric charges Proton, Electron and Neutron

Electric force Our society is dependent on electricity. An electric power failure demonstrates our dependence on electricity. Electricity is an essential ingredient in all the atoms in our bodies and in our environment. The forces that hold the parts of an atom together are electric forces. Furthermore, so are the forces that bind atoms in a molecule and hold these building blocks together in large-scale macroscopic structures, such as a rock, a tree, a human body, a skyscraper. Our immediate environment is dominated by electric forces. In the following chapters, we will study electric forces and their effects. For a start, we will assume that the particles exerting these forces are at rest or moving only very slowly. The electric forces exerted under these conditions are called electrostatic forces. We will consider the electric forces when the particles are moving with uniform velocity or nearly uniform velocity. Besides the electrostatic force there arises a magnetic force, which de

The frictional force that develops when two objects are at rest relative to each other is called static friction.

The effect of the smoothness of the road is observed on the motion of the car. For example, when driving on a rough road, the grooves of a car's type come in contact with the uneven parts of the road. As a result, frictional force occurs. This makes it easier for the car to move on the road and the car can be easily stopped by pushing the brake. But if the road is smooth, the grooves of a car\s type doesn't properly come in contact with the road. As a result, the car may side while moving or stopping. This causes inconvenience. 

According to Newton's second law of motion, the applied force is proportional to the change of momentum means, if a force with larger magnitude is applied on an object for a certain time period then the change of momentum will be greater and if a force with a smaller magnitude is applied on that same time period then change of momentum will be smaller. 

Frictional is the consequence of the surface irregularities of any two surfaces. Though the surface of an object seems to be smooth apparently, there are high and low grooves on it in fact. When an object moves on another object, the grooves of both the surfaces catch onto one another and this is why frictional force is produced. 

Galileo proposed three laws regarding falling bodies. These are laws of falling bodies. First law: All bodies falling from rest and from the same height without any resistance traverse equal distance at the same time. Second law: The velocity (v), acquired by a freely falling body from rest in a given (t) is directly proportional to that time. i.e,  v∞t . Third law: The distance(h) traversed by a freely falling body from rest in a given time(t) is directly proportional to the square of the given time. i.e, h∞t 2 .

 Whether an object is actually in rest or motion depends on the reference object. If the reference object or reference frame is actually at rest, the object at rest will be actually at rest with respect to that frame. This type of rest is called absolute rest. A body is said to be in absolute rest when it is at rest with respect to an absolute rest object. But in this universe, it is not possible to get a reference object which is at absolute rest. Since the earth is moving around the sun while the sun itself is moving along the galaxy with its planets and satellites. So, we can say that in this universe all rest and all motion are relative.  No rest or no motion is absolute.

 The atmosphere for its weight applies force on the earth's surface and the amount of force acting perpendicularly on per unit surface area of the earth is called atmospheric pressure. As the altitude increase, the length of the air column decreases. So, the weight it applies to per unit surface area i.e, pressure decreases with the increase of altitude from the surface. 

 Weight is a force that is a vector. So, it has a magnitude and direction. However, mass is a scalar. Weight and mass are related to one another, but they are not the same quantity. Mass is multiplied by the acceleration due to gravity to calculate the weight of an object. Acceleration due to gravity is directed vertically downward.  So, weight is also vertically downward. 

 If the acceleration of a body 5 ms -2  it means that the body is moving with a uniform velocity of 5 ms -1  each second; that is, its velocity is increasing every second at a rate of 5 ms -1 .

 The rate of change of velocity with the time that is the change of velocity is known as acceleration. It means to be accelerated, the magnitude or direction of the speed of a body must be changed. But if the magnitude of the velocity of a moving body remains unchanged, then the velocity of the body is called uniform or equal velocity.  So, a body moving with uniform velocity doesn't have acceleration.