Showing posts from April, 2014

Electromagnetic Induction:C.R.Q's /Questions

15.1 Does the induced emf in a circuit depend on the resistance of the circuit?does the induced current depend on the resistance of the circuit?
Ans. The Induced emf in a coil depends upon the rate of change of flux through it (E=-Nt) .Hence its value does not depend upon the resistance of the coil.But the induced current that flows through a coil is equal to I=E/R and it’s value depends on the resistance of the coil.If , resistance increases then the current flowing through the coil decreases.Because the product of I and R must remains constant.i.e. I x R = Constant.
15.2 A square loop of wire i moving through a uniform magnetic field.The normal to the loop is oriented parallel to the magnetic field.Is emf induced in th loop?Give a reason for your answer.
Ans.No, induced emf will not be produced because there is no change of flux linking to the loop.i.e.t=0 .So according to the relation (E=-Nt) ,E=0.If the square loop is being rotated in magnetic field in such a way that the loop is cut…

What is Non Newtonian Fluid?

Many people have heard of Sir Isaac Newton. He is famous for developing many scientific theories in mathematics and physics. Newton described how ‘normal’ liquids or fluids behave, and he observed that they have a constant viscosity (flow). This means that their flow behaviour or viscosity only changes with changes in temperature or pressure. For example, water freezes and turns into a solid at 0˚C and turns into a gas at 100˚C. Within this temperature range, water behaves like a ‘normal’ liquid with constant viscosity.

Typically, liquids take on the shape of the container they are poured into. We call these ‘normal liquids’ Newtonian fluids. But some fluids don’t follow this rule. We call these ‘strange liquids’ non-Newtonian fluids.

Stress and strain

In science, stress means that a force is applied to a body. The result of that stress is described as strain.

Imagine hitting a metal with a hammer. The force that is applied on the metal causes stress to that particular area. The result…

The ratio of the dimensions of G to those of g is..... ?

The dimension of G can be found by the formula F=Gm1m2/r2 i.e. G=F r2/ m1m2       Dimensions: [F]=MLT-2         [r]=L               [m]=M So [G] = MLT-2 L2M-2=M-1L3T-2 Now, the dimension of g is given by [g]=LT-1 Now, finding the ratio of G to g; ðM-1L3T-2/ LT-1 ðM-1 L2 T-1 
Hence it is the ratio of dimensions of G to the dimensions of g.

Types Of Galaxies

Many different types of galaxies exist. The different types of galaxies not only appear different, but have different evolutionary histories as well. The three fundamental classes of galaxies are elliptical, spiral, and irregular. These categories are further broken down into subclasses, often illustrated using a Hubble tuning fork diagram. Originally, scientists thought this diagram may have represented an evolutionary sequence for galaxies, but today we know that this is not true. The formation and evolution of galaxies is a complex process that is poorly understood.

Elliptical galaxies are so named because they have elliptical shapes: they look like fat, fuzzy eggs or footballs. Stars in ellipticals do not spread out into a thin disk, as they do in spiral galaxies; instead, they wrap evenly around the galaxy's center in all directions. Ellipticals have smoothly varying brightnesses, with the degree of brightness steadily decreasing outward from the center. If you l…

How lightning rod works?

The lightning rod, which Benjamin Franklin invented in 1749, is a metal pole mounted atop a building that draws lightning's electrical charge away from the structure.The rod is attached to an aluminium or copper cable that's connected to an underground conductive grid. This allows the electricity to dissipate harmlessly.
Because lightning tends to strike the tallest object in the vicinity, lightning rods must be taller than any buildings or other objects in the area.If installed properly, a lightning rod will carry a lightning bolt's electrical charge through the path of least resistance along the cable into the ground, reducing the risk of fire or heat damage from the strike.

Lightning looks for the easiest path to travel and lightning rods are good conductors of electrical current. If lightning strikes the rod, the electrical current is moved away from the house and is safely gotten rid of underground. Sometimes lightning strikes and then jumps around a bit, looking for…


Geiger counter is a portable device which is used for the detection and counting of ionized particles and radiation

It consists of a hollow metallic cylinder, one end of which is closed by an insulating cap. At the center of the cap is fixed a stiff straight wire along the axis of cylinder .A thin mica or glass disc closes the other end which also serves as the entrance window for ionizing particles. The tube contains a special mixture of air, argon, alcohol at a pressure of 50-100 mmHg.


A potential difference of the range of 1000V is maintained between the metal cylinder and the axial wire through a suitable series resistor of 109 ohms. When an ionizing particle enters the tube through the window, it ionizes some gas molecules in it. These ions are accelerated by the strong radial electric field producing more ions by collision which produces ionization current so a momentary current flows between the wire and the cylinder and also through the resistor …


It is an instrument used for the detection and identification of the path of subatomic particles.
In Wilson Cloud Chamber, paths of subatomic particles or ionized particles can be photographed.


When a particle is passed through the supersaturated vapours, droplets are formed on the line due
to ionization along the track and particle is detected.

It is consist of a closed cylinderical chamber with the transparent glass top,a movable piston at the bottom. On the sides near the top, the cylinder is provided with a glass window. inside the cylinder
a liquid of low boiling point is placed. The piston can be moved up or down. The whole system is air tight.A strong light source isused to illuminate the chamber while the photograph is taken by the
camera as shown.


Some volatile liquid having low boiling point (methanol CH3OH or ethanol C2H5OH) is poured on the inner surface of the chamber. The piston first is moved slowly up so that the ai…

Working of SCR - Silicon Controlled Rectifiers

In solid state S/C silicon controlled rectifier , anode terminal is always kept at positive potential w.r.t cathode terminal. The load is connected in the series with the anode .
The working of SCR circuit can be grouped as followings:
When gate is open:In the SCR circuit with no voltage is applied to the gate i.e open gate,junction J2 is reverse biased whereas J1 and J3 is forward biased connection . Therefore , the condition in the junction J1 and J3 is as similar as npn transistor with base open .As a result no current flows via the load resister RL.,at that time the SCR is cut off state.If the applied voltage in the circuit is slightly increased ,a stage is reached when junction J2 breakdown because of reverse biased . Now the SCR conducts rapidely and at that time SCR side to be ON state .The amount of the applied voltage at which SCR conducts rapidely with open gate is called break over voltage.

When gate voltage is applied : When the gate terminal is positive w.r.t cathode , her…

What is Boyle's Law?

Boyle studied the compressibility of gases in 1660. In his experiments he observed "At a fixed temperature, the volume of a gas is inversely proportional to the pressure exerted by the gas." The experiment is simple: (see figure on right)

A cylinder with a piston and a gas is immersed in a bath (e.g. water). The purpose of the bath is to have a ready heat source to maintain the temperature of the gas constant throughout the experiment. A mass is placed on top of the piston which results in a pressure on the gas. The gas volume is measured and 1/V vs P data point plotted. The mass is increased and the new 1/V vs P data point plotted. This is continued over several larger masses. to see what happens place the mouse cursor over the image.

The straight line impliesor

Which is Boyle's law.

Why pair production can not take place in vacuum?

The most basic conservation laws are conservation of energy, conservation of momentum and conservation of angular momentum. These laws are a result of the invariance of the fundamental equations of motion to moving the origin or rotating the axes of our coordinate system. In other words, the fundamental equations should look the same, regardless of how we choose our coordinate system. The mathematical theorem which relates the existence of these conservation laws to the invariance of the equations is called Noether's Theorem. 
The reason why a gamma-ray cannot create electron-positron pairs in a vacuum is that there is no way to do this without violating the conservation laws. Another fundamental invariance of the equations is Lorentz invariance, which means that the fundamental equations should look the same in all coordinate systems which can be related by a Lorentz transformation. A Lorentz transformation relates the equations in one coordinate system with the equations in ano…

What happens to capacitance of parallel plate capacitor when the size of plates increase and distance between them decrease?

There are three basic factors of capacitor construction determining the amount of capacitance created. These factors all dictate capacitance by affecting how much electric field flux (relative difference of electrons between plates) will develop for a given amount of electric field force (voltage between the two plates):

PLATE AREA: All other factors being equal, greater plate area gives greater capacitance; less plate area gives less capacitance.

Explanation: Larger plate area results in more field flux (charge collected on the plates) for a given field force (voltage across the plates).

PLATE SPACING: All other factors being equal, further plate spacing gives less capacitance; closer plate spacing gives greater capacitance.

Explanation: Closer spacing results in a greater field force (voltage across the capacitor divided by the distance between the plates), which results in a greater field flux (charge collected on the plates) for any given voltage applied across the plates.


How do electrons and holes flow in a transistor ?

We will now explain the operation for the transistor, using an NPN type. The same operation applies for the PNP transistors as well, but with currents and voltage sources reversed.

With no power applied to the transistor areas,
there are two depletion zones between the two P-N contacts. Suppose now that we connect a power source between the base and the collector in reverse-bias, with the positive of the source connected to the collector and the negative to the base. The depletion zone of the P-N contact between the base and the collector will be widened. Moreover, a slight current will flow withing this contact (due to impurities). This current is the reverse contact current and we will use the symbol ICBO:

Now suppose that we connect another voltage supply between the emitter and the base in forward bias, with the positive of the source connected to the base and the negative connected to the emitter. The depletion zone between the emitter and the base will be shortened, and curren…