Thursday, January 31

Right Angle Mirror

Introduction to right angle mirror:

Any smooth polished surface, which can return the rays of light into the same medium, is called mirror. Looking glass is the best example of mirror. Any highly polished metal surface also acts as a mirror. Still water or oil have a smooth surface and hence acts like a mirror. Even highly polished furniture or the utensils acts like a mirror. Here we discuss the right angle mirror. I like to share this equation for converting celsius to fahrenheit with you all through my article.

Right Angle Mirror

If the two mirrors are arranged so that they inclined at an angle of 90° to each other are called the right angle mirrors. Mirrors are based on the optical phenomenon called reflection. When a ray of light traveling from one optical medium to another optical medium it bounces back from the interface with the change of the angle is called reflection. We can see our image in the looking glass due to the phenomenon of reflection of the light falling on us. Now let us consider that the two plane mirrors M and N are placed at right angle to each other as shown in the diagram.

Let them intersects at point O. Now an object is placed between the mirrors. We get three images of this object. As we know that the number of images formed by the mirrors which are inclined at an angle `theta`° is given by 360 / `theta` - 1 (if 360 / `theta`  is an even number). So, we get the three images formed by this system of the mirrors.

Conclusion for the Right Angle Mirrors

Here we conclude that the images formed by the system of the right angle mirrors is virtual that means we cannot get these images on the screen. The size of the images is same as that the object. The image formed is laterally inverted. The system of the right angle mirrors are used in the solar cookers, kaleidoscopes, periscopes etc. Generally, we use two plane mirrors to make the right angle mirror system but in the different condition and for the several purposes we use the combination of the plane and spherical mirrors.

Speed Practice Problems

Speed of an object is defined as the distance covered by it in per unit time interval. It is obtained by dividing the distance covered by the object by the time it takes to cover that distance.

Therefore ,                                    Speed = Distance covered / Time taken

The speed practice problems can be solved by using the above formula.

Here are some of the speed practice problems:

Speed Problems

Problem:  A train crosses a pole in 15 seconds. If the length of the train is 300 meters, find the speed of the train. (Answer: 20 m/ sec).

Solution : Speed = Distance / time

Speed =  300 / 15

Speed = 20 m / sec is the answer.

Practice Problems on Speed.

Problem: Brittany walking at a speed of 20 km/h reaches her college 10 minutes late. Next time she increases her speed by 5 km/h, but finds that she is still late by 4 minutes. What the distance of the college from her house?(Answer: 10 km).

Problem: The average speed of Ryan for a 6 hrs journey is 45 km/h. If he travels with the speed of 40 km/h for the first four hours , find the average speed for the last two hrs.

Problem: X and Y are two stations 600 km apart. A train starts from X and moves towards Y at the rate of 25 km/hr. Another train starts from Y at the rate of 35 km/hr. How from X they will cross each other? (Answer: 250km)

Problem: The boat goes 15 km upstream in 80 minutes. The speed of the stream is 5 km/h. What is the speed of the boat in still water? (Answer: 16.25 km/hr)

Problem: A motorboat whose speed in still water is 15 kmph goes 30 km downstream and coves back in a total 4 hours and 30 minutes. Determine the speed of the stream. (Answer : 5 kmph)

Problem:  Alex average speed for the 5 hours is 10 miles per second. His average of the next three hours is 15 miles per hour. Find the average speed for the total 8 hours. (Answer: 11.87 miles per hour).

Thursday, January 17


Introduction to demagnetization:

The reverse process of magnetization in which a magnet loses part or whole of its magnetism is called demagnetization. Not only magnets or magnetized pieces of iron, but also the unmagnetised pieces of iron are constituted of molecules that themselves are magnetic character. Each molecular magnet possesses a north pole and a south pole. The reason why an unmagnetised pieces of iron does not exhibit magnetic properties although it itself is made up of magnets is that different molecular magnets form closed group so that the effect of the north pole of one of the molecular magnets on a neighbouring molecular magnet is exactly counterbalanced by the opposite pole of the other molecular magnet situated very closed to it.

Methods of Demagnetization

1.Rough handling: it is observed that if a magnet is subjected to rough treatment such as dropping from a height or hammering then it gradually loses part or whole of its magnetism.

The rough handling disturbs the alignment of some of molecular magnets so that the magnetization would become weak.

2. Heating: A magnet is found to lose its magnetism when heated. The quantity of magnetism lost would depend on the temperature to which it is heated. On heating a magnet, the internal energy of the molecular magnets increases. This results in more violent vibrations of the molecules, so that their alignment in a given direction is disturbed and the magnetization becomes weak.

Special Cases of Demagnetization

Electrical method: A long coil (solenoid) of insulated copper wire is connected to a source of alternating current. The magnet is placed inside this coil so that the magnet is along east-west direction. The current is switched on and the magnet is pulled out of the coil. When checked the magnet is found to possess no magnetism.

Self-demagnetisation: It is observed that the magnets lose their magnetism of their own accord.

Momentum Vectors

Introduction to momentum vector:

Measurement of motion of a body can be explained by momentum vector.

Definition of momentum vector:

Momentum vector is defined as the total motion contained in the body. Mathematically, momentum vector is equal to the product of mass of the body and its velocity. I like to share this Conservation of Linear Momentum with you all through my article.

P = m × v

Where m is the mass of the body and v be the velocity of the body.

Momentum vector is a vector quantity. The unit of momentum vector is kg m /s in MKS and g cm /s in CGS.

Principle of Conservation of Momentum Vector:

It states that if no external force is applied on a system, then the momentum of the system remains constant. In other words, if there is no external force applied on the system,

the initial momentum of the system will be equal to the final momentum of the system Consider a system of two bodies on which there is no external force acting on it. Because the system is isolated from the surroundings, so it interacts only due to their mutual interactions. Due to the mutual interaction, the momentum of the individual bodies may change but the total momentum of the system remains constant. If q1 and q2 be their individual momentum's, then Please express your views of this topic elastic collision formula by commenting on blog.

q1 + q2 = constant

For a system of n bodies, we can say that, q1 + q2 + q3 +…..+ qn = constant

Practical Application of Principle of Conservation of Momentum Vector:

When a bullet is fired from the gun, the gun recoils or gives a jerk in the shoulder in the backward direction. Let M be the mass of gun and m be the mass of the bullet. Initially both bullet and the gun are at rest. On firing the gun, suppose that the bullet moves with velocity v and the gun moves with velocity V. As we use the principle of conservation of momentum,

Total momentum of the gun and the bullet before firing = total momentum of the

bullet and the gun after firing

0 = MV + mv

V = - mv / M

The negative sign shows that the gun will move in the opposite direction of bullet.

Thursday, January 10

Forms of Heat Transfer

Introduction to forms of heat transfer
The science of heat transfer is concerned with the estimation of the rate at which heat is transferred, the duration of heating or cooling for a certain heat duty and the area required to accomplish that duty.

There are three different forms of heat transfer : 1. conduction 2. convection 3. radiation

Conduction form of heat transfer

It is the  heat transfer between two bodies or two parts of the same body through molecules which are more or less stationary. In liquids and gases conduction results from the transport of energy by molecular motion near the wall and in solids it takes place by a combination of lattice vibrations and electron transport. The law which determines this conduction heat transfer is called as Faraday's Law. This law states that the rate of heat flux is linearly proportional to temperature gradient.

Convection Form of Heat Transfer

It is the heat transfer that occurs because of the motion of a fluid past a heated surface - the faster the motion, the greater the heat transfer.  The convection heat transfer is usually assumed to be proportional to the surface area in contact with the fluid and the difference in temperature of the surface and fluid. This is also called as Newton's law of convection. When a temperature difference produces a density difference which result in mass movement, this process is called as free or natural convection. When the mass motion of fluid is caused by an external device like a pump, compressor, blower or fan, the process is called the forced convention. Here the fluid is made to flow along the hot surface and heat is transferred from the wall to the fluid.

Radiation Form of Heat Transfer

It is the heat transfer which is the result of electromagnetic radiation emitted by a surface because of the temperature of the surface. This differs from other form of electromagnetic radiation such as radio, television, X-rays, Gamma rays which are not related to the temperature.The best example of this is the heat receiving from the sun. The laws which govern this type of heat transfer are:

a. Kirchhoff's law

b. Stefan's law

c. Stefan- Boltzmann's law

Diffraction Limited

An introduction to diffraction limited:

The ability to produce images of an optical system with the angular resolution after overcoming the imperfections of the lenses is called as diffraction Limited. The optical instruments like Telescope, Microscope and camera are said to be Diffraction Limited if they give enough accuracy. Let us discuss more on diffraction limited. I like to share this Define Emp with you all through my article.

Discussion on Diffraction Limited

In Physics this Diffraction -Limited of the instrument is independent of imperfection due to other substances. It depends only on the limit of the optical power of the instrument. Like the diffraction of the telescope does not depend on the turbulence of the atmosphere. The resolution of an instrument is proportional to the size of the object and inversely proportional to the wavelength of the observed light. For telescope of circular apertures, size of the smallest feature in an image that is diffraction limited is size of the airy disc. One more important term is there to describe this topic better is Rayleigh’s limit. Rayleigh’s limit is the telescope’s ability to separate closely situated stars. The visual Rayleigh’s limit for a 203mm aperture telescope is 0.69arc seconds. Another limit is Dawes Limit that is 0.57arc second. The accuracy of radio telescope is much higher than normal telescope because they use very long wavelength which minimize the atmospheric distortion. Please express your views of this topic Formula of Density by commenting on blog.

Techniques on Diffraction Limited

The two techniques are there for diffraction limit, they are near field technique and Far field technique.

Near field technique- The Near field technique is applied for light of less than 2 wavelength.This technique gives that information beyond Diffraction –Limit.It is used to construct very high resolution image .It is used in total internal reflectance microscopy and metamaterials.It gives better result by placing objective lens extremely close to the object.As Near field technique cannot give the image more than 1 wavelength, so it can’t use in thicker than 1 wavelength. That’s why the practical uses of this technique are rare.

Far Field Technique-This is the best technique to use for imaging objects having large wavelength. It uses in biological applications like cells. This technique usually exploit optical non-linearity in material’s reflected light to generate resolution beyond the diffraction limit.

Conclusion for Diffraction Limited

A Laser beam is also called Diffraction Limited if its beam quality is ideal. In that case the laser beam focused to a small spots is as high as possible for the given wavelength. For advice on how to measure the beam quality of your laser source, or how to optimize.

Thursday, January 3

Kinetic Theory

Kinetic Theory of Matter Definition : We Define Kinetic Theory as explanation which predicts the behavior of matter or motion of its particles on certain assumptions and observations.  The Kinetic Theory of Matter considers that matter is composed of very small particles or molecules which are always in motion. The Kinetic Theory gives the difference between the three elementary states of matter. This theory assumes that the matter is composed of small particles, particles are in constant or continuous motion.
Solid matter consists of particles which are so closely packed that they can vibrate only but cannot move.  In liquid matter particles are little far from each other but still close enough that the force of attraction that it takes the shape of container. The movement of the particles in liquid is confined in the volume of liquid. In gaseous matter the particles are free to move, they are very far from each other and have large kinetic energy. I like to share this Average Kinetic Energy Formula with you all through my article.

Because of the random movement, particles (liquid and gas) collide with each other and with the walls of container.  The collision between particles takes place without any change in net energy but exchange energy among them. Hence collision is perfectly elastic.
The movement of particles decides their kinetic energy through formula: KE=½mv2, m is mass and v is velocity of particle. This kinetic energy of particles decides the thermal energy or temperature of the matter. Temperature is actually the average kinetic energy of the particles of a matter.
Transfer of heat takes place from a matter of high temperature to low temperature. High temperature particles move or vibrate with high speeds and when they collide with nearby particle of less temperature (less KE), they exchange KE to them (hence increases temperature of neighbor particles). Now these particles start vibrating or moving fast and gives energy to their neighbor particles and so on. Hence thermal energy transfers from high to low temperature. So, kinetc theory explains the flow of heat by conduction which is flow of heat-energy through a matter. I have recently faced lot of problem while learning Activation Energy Formula, But thank to online resources of math which helped me to learn myself easily on net.

Kinetic Theory of Gas says that a gas consist of large number of very small particles of same mass which move continuously and randomly with certain speed. These particles collide perfectly elastically with each other and with the walls of the container.  It explains the properties, temperature, pressure and volume of gas.
Pressure due to particles on walls=(Nm2)/(3V)
Temperature T= (m2)/(3kB)
Kinetic energy=½Nm2
is average velocity of particles, N is no. of gas molecules,V is volume, m is mass of molecules, kB is Boltzmann constant.