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# Monthly Archives: September 2012

## Problems from Electricity

1. The parallel plates of an air filled capacitor with area of area 1.1 x 10^8 m^2 . What must be the width of the plate be if the Capacitance is 1 Farad?
2. Four capacitor each of 2microfarad are connected in such a way that total capacitance is also 2microfarad. Show what combination gives this value. Also try to illustrate the diagram.

(Fari posted these)

1.Using the formula: $C=&space;A\varepsilon&space;/d$

and substituting , C= 1 F, A = 1.1 x 108, $\varepsilon$ = 8.8 x 10-12,

we get  , d =9.68×10-4 metres

2.

## Laws of motion – The problem of descending balloon.

A balloon is descending with a constant acceleration ‘a’ less than acceleration due to gravity. The mass of the balloon, with its basket and contents, is M. What mass m, of ballast(sand bags) should be released so that the balloon will begin to accelerate upward with constant acceleration ‘a’?

Posted by  Anisha Banerjee

## How do the protons fly almost at a speed of light in LHC at CERN?

How do the prortons fly almost at a speed of light in LHC at CERn.What gives them so much acceleration?please clarify…If i want to study Particle physics in future what qualifications I would need.I want to be a scientist at CERN?Please clarify.

Posted by Nabasindhu DAs

Hi! First of all we would like to congratulate you on your wish and dream to join CERN.

The acceleration of protons are done by huge particle accelerators.

The Currently active machines are:
Two linear accelerators generate low energy particles. Linac2 accelerates protons to 50 MeV for injection into the Proton Synchrotron Booster (PSB), and Linac3 provides heavy ions at 4.2 MeV/u for injection into the Low Energy Ion Ring (LEIR).[16]
The Proton Synchrotron Booster increases the energy of particles generated by the proton linear accelerator before they are transferred to the other accelerators.
The Low Energy Ion Ring (LEIR) accelerates the ions from the ion linear accelerator, before transferring them to the Proton Synchrotron (PS). This accelerator was commissioned in 2005, after having been reconfigured from the previous Low Energy Antiproton Ring (LEAR).
The 28 GeV Proton Synchrotron (PS), built in 1959 and still operating as a feeder to the more powerful SPS.
The Super Proton Synchrotron (SPS), a circular accelerator with a diameter of 2 kilometres built in a tunnel, which started operation in 1976. It was designed to deliver an energy of 300 GeV and was gradually upgraded to 450 GeV. As well as having its own beamlines for fixed-target experiments (currently COMPASS and NA62), it has been operated as a proton–antiproton collider (the SppS collider), and for accelerating high energy electrons and positrons which were injected into the Large Electron–Positron Collider (LEP). Since 2008, it has been used to inject protons and heavy ions into the Large Hadron Collider (LHC).
The On-Line Isotope Mass Separator (ISOLDE), which is used to study unstable nuclei. The radioactive ions are produced by the impact of protons at an energy of 1.0–1.4 GeV from the Proton Synchrotron Booster. It was first commissioned in 1967 and was rebuilt with major upgrades in 1974 and 1992.
REX-ISOLDE increases the charge states of ions coming from the ISOLDE targets, and accelerates them to a maximum energy of 3 MeV/u.
The Antiproton Decelerator (AD), which reduces the velocity of antiprotons to about 10% of the speed of light for research into antimatter.
The Compact Linear Collider Test Facility, which studies feasibility issues for the future normal conducting linear collider project.

The LHC is the world’s largest and highest-energy particle accelerator

The collider is contained in a circular tunnel, with a circumference of 27 kilometres (17 mi), at a depth ranging from 50 to 175 metres (160 to 574 ft) underground.

Prior to being injected into the main accelerator, the particles are prepared by a series of systems that successively increase their energy. The first system is the linear particle accelerator LINAC 2 generating 50-MeV protons, which feeds the Proton Synchrotron Booster (PSB). There the protons are accelerated to 1.4 GeV and injected into the Proton Synchrotron (PS), where they are accelerated to 26 GeV. Finally the Super Proton Synchrotron (SPS) is used to further increase their energy to 450 GeV before they are at last injected (over a period of 20 minutes) into the main ring. Here the proton bunches are accumulated, accelerated (over a period of 20 minutes) to their peak 7-TeV energy, and finally circulated for 10 to 24 hours while collisions occur at the four intersection points.

More technical details can be had at the following links, including the ways to join CERN

## Rotational Equilibrium – A Numerical Problem

A father and his son are supposed to carry a load of 500 N. They decided to use a uniform pole that is 4.0 m long and weighs 60 N. The father and his son support the pole at the ends. Where should the load be placed so that the father supports three times as much as his son?

Posted by Daniel

Let’s represent the situation be the folowing diagram

Let the force exerted by son be f

Then the force exerted by father = 3f

Therefore the total force exerted =Total weight = 560N = 4f

Which gives f = 140 N, the force exerted by son

3f=420 N, the force exerted by father

Applying the principle of moments about the point where father holds the rod,

420 x 0 – 500 x x – 60 x 2 + 140 x 4 = 0

==> x = 440/500 = 0.88 m from the end where father holds the load

(If there is any problem you find in the solution given, please post as comment to this post.)

## How to do questions of mechanics efficiently?

How to do questions of mechanics efficiently???????????????????????
although hcv done but unable to solve new problems ………….hcv done with the help of solutions..help me

Sarthak  posted

We cannot just state all the tactics in a go, as the individual problems differ from each other and the techniques and tactics required are different.

However, these are some suggestions which will help you to solve the problems in Mechanics (and Physics in general)

• Visualize the problem.  You should be able to imagine and visualize the situation given in the problem. Draw diagrams to illustrate. Write in all the necessary details along with
• Write the physical quantities given, assumed and to be found using accepted notations. This will help you to zero in on the correct formula
• … To be continued

## Why there are Sine functions in Physics?

Why are sine functions used in some of the equations in physics?
For example,in the expression for instantaneous emf induced in a rotating conductor placed in an uniform magnetic field which is given by
E=B*L*V*sin(theta)
where,
B is the strength of the magnetic field,L is the length of the conductor and (theta) is the angle between the direction of motion of the conductor and the magnetic field,and here,my question is why do we use sine function in this expression?what is its need?

The function sin (theta) in a right angled triangle = opp. side /Hypotenuse

When we have to take a component perpendicular to another, we take the sine function.

## Force on a moving charge problem

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