January 28, 2018

Q. Explain Principle, Purpose and Features of Nuclear Reactors

NUCLEAR REACTOR


DEFINITION:

Nuclear reactor is a device which is used to perform controlled fission reaction and extract the hidden energy from the nucleus.

PURPOSE:

Following are some main purpose of the nuclear reactor.
1- To convert controlled fission reaction to controlled chain reaction.
2- To produce large amount of energy.
3- To produce radioisotopes.

PRINCIPLE:

It is used on the principle of nuclear fission a process in which heavy nucleus breaks in to lighter nuclei with the emission of large amount of energy”.

FEATURES OF NUCLEAR REACTOR:

Following are the general features, which are common or almost nuclear reactor.

1. NUCLEAR FUEL:

A Material consisting of the fissionable isotopes is called reactor fuel that may be used in a reactor. For example (Uranium 92U235).

2. MODERATORS:

In the nuclear fission process at least one or more neutrons are produce per fission. To reduce the energy of neutron some suitable material is required which are known as moderators. The ordinary water (light water) an attractive moderator because of its supply at low cost. Heavy water is the best material. Other moderator is graphite beryllium and its oxides and organic compound.

3. COOLANTS:

Huge amount of heat is generated in reactor core as a result of fission take place in the
unclear fuel. To remove this large amount of heat, material are required which are called coolant. These materials are circulated though the core in order to absorb heat and transfer it to the outside of the core.

4. CONTROL MATERIAL:

In order to control nuclear fission in a reactor, suitable neutron absorbing material is required to be placed in the core region. The control material should be such that it does become radioactive by neutron capture. Cadmium and boron are good control materials.

5. SHIELDING:

During nuclear reactions neutrons and gamma rays emits out and becomes hazardous in the vicinity of the reactor, therefore proper shielding material is always required. A shielding material used for such protection is called the biological shielding because its purpose is to protect health. Generally a layer of concrete about 6 to 8 feet thickness has been found to absorb both neutrons and gamma rays. For rector operating at high power thermal shielding is required. A few cm of iron or steel very close to the core of the reactor provide the required thermal shield.


January 23, 2018

How Hydraulic Brakes work?

      The working of hydraulic brakes is based on the principle of Pascal law. These brakes are used in automobiles. It consists of a tube which contains oil called brake oil. One end of the tube is fitted with a piston working in a master cylinder. There are in all four tubes through which the master cylinder is joined to four small cylinders (each containing a piston of large area) one for each wheel of the automobile. These small cylinders are called brake cylinders. When the brake pedal is pressed by applying a force, the piston in the master cylinder begins to move inside the tube and exerts pressure on the oil. This  pressure is transmitted to the oil in the brake cylinder. The undiminished transmitted pressure pushes the piston in brake cylinder which acts as a brake shoe attached to a caliper. The resulting friction stops the wheel. When the pressure on the pedal is released, the spring which connects the two brake-shoes contracts and pulls them off from the rotor. Thus the wheel is again free to rotate.

Image result for hydraulic brakes

January 19, 2018

WORK-ENERGY RELATION


WORK ENERGY EQUATION

DERIVATION:
            Let us consider a body of mass “m” is placed at point A at a height h from the surface of earth.At this point the body possesses gravitational potential energy equal to mgh w.r.t point C lying on the ground.
            Now consider a point B at a distance x below the point A during downward motion of body.At this stage the height of the body becomes (h-x).

so, potential energy at point B becomes,
                                                P.E=mg(h-x)
As we know that potential energy at point B is less than the potential energy at point A,i.e.
                                                mg(h-x) < mgh
            or                                 mgh – mgx <mgh

            The loss in potential energy at point B is mgx.
           
The Kinetic Energy at point A is equal to zero because the body is at rest.During its downward motion its velocity increases ,so its kinetic energy also increases.If there is no air friction then the loss of P.E is equal to the gain in K.E, means P.E is converted into K.E.

            When the body reaches at point C its P.E becomes zero which means all of its P.E is converted into K.E,so we can write as
Loss in P.E = Gain in K.E

Practically there is always a force of friction which opposes the downward motion of the body.Let if friction f is present in this case then some amount of P.E is lost in work done against friction.Now, the modified equation can be written as,

                        Loss in P.E = Gain in K.E + Work done against friction
                                    mgx= 1/2 mv2 + fx
or                                 1/2 mv2 = mgx – fx

In terms of “h”
                                      1/2 mv2 = mgh – fh

            The above equation is known as “Work Energy Equation”.