## Sunday, October 30, 2011

### Physical World and Measurement

Topic - Physical World and Measurement

### Kinetic Energy - Numerical Problem

a running man has half the kinetic energy that a boy of half his mass has.the man speed up by 1m/s and then has the same kinetic energy as the body. what were the original speeds of man and boy?

### Spherical Mirror Problem

A rear view mirror used in a bus has a radius of curvature 3.5 m. If the driver of the bus locates a car at 10.0m behind the bus, find the position, nature and size of the image of the car.

Ans:

f = r/2=-1.75 m

u=-10m

v=?

$\LARGE \inline f=\frac{uv}{u+v}$

$\LARGE \inline v=\frac{uf}{u-f}$
$\LARGE \inline v=\frac{-10 \times -1.75}{-10-(-1.75))}=\frac{17.5}{8.25}=2.12m$

## Friday, October 28, 2011

### Parallel Universe

Is there really a parallel universe?

As of now, the answer is not final. There are different ideas and explanation given on parallel universes. Some say if parallel universe are far away from us, whereas others say that they are very close to us.

String theorists say that there are actually 11 dimensions. They'd come to the conclusion that our Universe is just one bubble among an infinite number of membranous bubbles which ripple as they wobble through the eleventh dimension.

If we think on probability also, we cannot just be selfish to say that we are alone. There is an equal probability of many such universes with life too.

I feel the space is not sufficient to explain all these thing here. The following links will help you know further.

http://space.mit.edu/home/tegmark/multiverse.pdf

http://www.scientificamerican.com/article.cfm?id=parallel-universes

http://www.bbc.co.uk/science/horizon/2001/paralleluni.shtml

http://en.wikipedia.org/wiki/Parallel_universe_(fiction)

### Dual nature of light and related questions

How light has a dual nature?

A photon has zero rest mass. Explain how ?

(These questions were posted by Shubham SInha  and Ritika Chatak)

The dual nature of light has been established through the various theories in an attempt to find out the real nature of light. The first theory on the nature of light was by Sir Isaac Newton. He said that light consists of tiny spherical an perfectly elastic particles called corpuscles which travel through space with an enormous speed. This theory could explain various phenomena exhibited by light like, reflection, refraction, rectilinear propagation etc. But could not explain color vision, colors in thin films, dispersion etc.

Then came Huygen's wave theory which considered light as mechanical waves. This theory could explain many phenomena but could not explain how light can travel through vacuum, as a mechanical wave requires a medium for propagation.

Then Electromagnetic Wave Theory  by James Clark Maxwell was used to explain the nature of light and it was experimentally established. The velocity of electromagnetic waves predicted theoretically matched closely with the actual velocity of light determined experimentally by different scientists through different methods.

But, the discovery of photoelectric effect made us rethink. Photoelectric effect, in which electrons are emitted out when light strikes the surface of metals, could be explained well only if we consider the particle nature of light.

Max Planck in his Quantum theory considers radiations as packets of energy called quanta (plural of quantum) or photons. These photos can behave like a particle during its interaction with matter and posses wave nature as basicllay light is an electromagnetic wave.

Thus scientists have concluded that light possess both wave nature and particle nature at the same time. In order to explain some phenomena we may consider its wave nature whereas for some other , we have to consider it as particle.

## Sunday, October 23, 2011

### What is Eddy Current?

Eddy currents are circulating currents induced in the body of a solid conductor whenever the magnetic flux linked with it changes. It is called EDDY CURRENT because they are like eddies formed in water.

http://youtu.be/zJ23gmS3KHY

## Saturday, October 22, 2011

### Numerical problem from image formation by spherical mirror - optics

An object is placed 18cm in front of a spherical mirror. if the image formed is 4cm to the right of the mirror calculate the focal length and radius of curvature? what is the nature of the mirror?

(The question was posted by Anisha)

## Friday, October 21, 2011

### Principle, construction and working of AC generator

Describe the Principle construction and working of AC Generator

### Height of Antenna and range of transmission

A TV Tower has a height h. Derive expression for the maximum distance upto which signals can be received on earth.

[caption id="attachment_8663" align="alignleft" width="300" caption="Height of Antenna and Range of Transmission"][/caption]

### Electric Current and flow of electrons

I have read that the FLOW OF ELECTRONS is called electricity. I wanna know that what is meant by flow of electrons? Pleaz answer me….

Electric current is the flow of charges. (Measured as the rate of flow of charges).

In conductors electric current is caused by the flow of free electrons. When a potential difference is applied across a conductor, the electrons are accelerated towards the positive potential. (But, due to the presence of plenty of electrons, they cannot move with acceleration as they collide with each other during their motion.) There is a net drift of electrons across any cross section and a current is developed.

### Three Indian Students bagged NASA awards

Three Indian students from top Indian educational institutions bagged NASA awards. These students have designed and launched their own satellites and have won the US space agency's student competition (foreign category) challenge. The three institutions are Indian Institute of Technology-Kanpur (IIT-K), Anna University of Chennai, and SRM University, according to National Aeronautics and Space Administration (NASA) website.

hey developed a conceptual aircraft named SERA (SRM Environmentally Responsible) Airliner’.

The team designed an airplane for 200 passengers incorporating efficient technologies in many aspects like fuel efficiency, aerodynamic performance with small take-off and landing distances.

## Wednesday, October 19, 2011

### A Presentation on BiJunction Transisitor

Sajan Shared this presentation on BJT. Please have a look at the slide notes too

Bipolar-Junction-Transistors-BJTs

## Friday, October 14, 2011

### Yarns made of the tiny straws of carbon called nanotubes have an astounding ability to twist as they contract, scientists have found

The team of researchers from Australia, the US, Canada and South Korea demonstrated motors that could spin at nearly 600 revolutions per minute, turning a weight 2,000 times heavier than the yarn itself.

### Work, Power, Energy & Human Powered Aircraft

Human-powered aircraft require a pilot to pedal, as in a bicycle, and produce a
sustained power output of about 0.30 hp.

The Gossamer Albatross flew across the English Channel on June 12, 1979, in 2h 49 min.

(a) How much energy did the pilot expend during the flight?

(b) How many Snickers candy bars (280 Cal per bar) would the pilot have to consume to be “fueled up” for the flight?

[Note: The nutritional calorie, 1Cal, is equivalent to 1000 calories (1000 cal) as defined in physics. In addition, the conversion factor between calories and joules is as follows: 1Cal = 1000 cal = 1 kcal = 4186 J. ]

### Numerical Problems from Light

Madhu sent us the following problems from "Light". Visitors can attempt to solve the problems by quoting the question number.

Most of the questions below are based on mirror formula and lens formula.

Mirror Formula

$\LARGE\frac{1}{u}+\frac{1}{v}=\frac{1}{f}$

Lens Formula

$\Large \frac{1}{v}-\frac{1}{u}=\frac{1}{f}$

Now try solving these questions/problems. If in doubt or not able to solve the problems, just post your problems as comments and we are here to help you out.

1. A rear view mirror used in a bus has a radius of curvature 3.5 m. If the driver of the bus locates a car at 10.0m behind the bus, find the position, nature and size of the image of the car.

2. An object 4cm high is placed at a distance of 6 cm in front of a concave mirror of focal length 12 cm. Find the position, nature and size of the image formed.

3. An object 50 cm tall is placed on the principal axis of a convex lens. Its 20cm tall image is formed on the screen placed at a distance of 10 cm from the lens. Calculate the focal length of the lens.

4.  A concave lens has focal length 20cm. At what distance from the lens a 5 cm tall object should be placed so that it forms an image at 15 cm from the lens? Also calculate the size of the image formed.

5. An object 2.0 cm in size is placed 20.0 cm in front of a concave mirror of focal length 10.0 cm. Find the distance from the mirror at which a screen should be placed in order to obtain a sharp image. What will be the size and nature of the image formed?

6. A convex lens has a focal length of 30 cm. Calculate at what distance should the object be placed from the lens so that it forms an image at 60 cm on the other side of the lens. Find the magnification produced by the lens in this case.

7. The radius of curvature of a convex mirror used on a moving automobile is 2.0 m. A truck is coming behind it at a constant distance of 3.5 m. Calculate (i) the position and (ii) the size of the image relative to the size of the truck. What will be the nature of the image?

8. Find the position of an object which when placed in front of a concave mirror of focal length 20 cm produces a virtual image, which is twice the size of the object.

9. A concave mirror of focal length 20 cm forms a real, inverted image of same size as that of the object. Where is the object placed with respect to the mirror? Draw a diagram to show the image formation?

10. The radius of curvature of a concave mirror is -46cm.What is its focal length?

11. A convex mirror used on an automobile has radius of curvature of 2 m .If a car is located at 4 m from the mirror, find the position nature and size of the image

12. An object is kept in front of a concave mirror of focal length 20cm.The image formed is three times the size of the object. Calculate the two possible distances of the object from the mirror.

13. An object 4cm high is placed 15cm away from a concave lens of focal length 10cm. Draw a ray diagram and find the position, size and nature of the image formed.

14. An object 0.4m high is placed at a distance of 0.8m from a concave mirror of radius curvature 0.4m. Find the position, nature and size of the image formed?

15. Two thin converging lenses of focal length 15cm and 30cm are held in contact with each other. Calculate the power and focal length of combination.

16. You are required to obtain an erect image of an object placed in front of a concave mirror of focal length 15cm.What should be the approximate distance of the object from the pole of the mirror? What is the nature of the image? Is the image larger of smaller in size than the object? Draw a ray diagram to show the formation of image.

17. An object of size 5cm is placed at a distance of 25cm from the pole of a concave mirror of radius of curvature 30cm.Calculate the distance and size of the image so formed. What will be the nature of the image?

18. An object of size 3cm is placed at a distance of 15cm from a convex lens of focal length 10cm.Calculate the distance and size of the image so formed. What will be the nature of the image?

19. A 1cm high image is obtained on a screen a t a distance of 20cm from a convex lens of focal length 10cm.What is the size the object?

20. The radius of curvature of a convex mirror is used on a moving automobile is 2.0 m. A truck is coming behind it at a constant distance of 3.5 m. Calculate (1) the position, and (2) the size of image relative to the size of the truck. What will be the nature of the image?

21. A concave lens of focal length 15 cm forms an image 10 cm from the lens? How far is the object placed from the lens?

22. An object of size 3 cm is placed at a distance of 15 cm from a convex lens of focal length 10 cm. Calculate the distance and the size of the image so formed. What will be the nature of image formed?

23. A converging mirror forms a real image of height 6 cm of an object of height 2 cm placed 20 cm away from the mirror. Find the image distance and the focal length of the mirror.

24. An object is placed at a distance of 10cm from a convex mirror of focal length 15 cm. Find the position and nature of the image

25. An object 5 cm in length is held 25 cm away from a converging lens of focal length 10cm. Draw the ray diagram and find the position, size and nature of the image formed.

26. An object is placed at 10cm in front of a concave mirror of focal length 15cm. Find the position, nature and size of the image

## Wednesday, October 12, 2011

### A Numerical Problem - Kinamatics

A particle is thrown vertically upward with a velocity of 19.6 m/s. Find (a) the acceleration of the particle at the highest point. (b) How high the particle will rise? (c) Time taken for rising to highest point.

## Monday, October 10, 2011

### Charge moving in a magnetic field

A particle of mass m with charge  q moving with uniform speed v normal to a uniform magnetic field describe a circular path of radius r. Derive expression for (1)time period of revolution and (11) kinetic energy of the particle.?

### Motion in a vertical circle and conservation of energy

A stone  tied to a string of length l is whirled around a vertical circle with the other end of the string at the centre. At a certain instant of time the stone is at the lowest position and has a speed u. What is the magnitude of change in its velocity as it reaches a position where the string is horizontal?

Let's assume that the potential energy at the lowest position be zero. So, when the string is horizontal, the stone has risen by a vertical height l, the length of the string which is also the radius of the vertical circle.

If v is the magnitude of velocity at the horizontal position, then according to the law of conservation of energy,

KE+PE at the lowest position = KE+PE at the horizontal position

$\frac{1}{2}mu^{2}=\frac{1}{2}mv^{2}+mgl$

From the equation above, v-u can be calculated.

$v=\sqrt{u^{2}-2gl}$

The following links will help you for deeper understanding and you can browse through some solved problems from the topic too.

### Coherent and incoherent addition of waves

If the waves are coherent, then the resultant intensity is given by

I = I1 + I2 + 2 √(I1 I2 Cos Θ), where Θ is the phase difference between two waves. For the constructive interference the value of Θ = 0°, so that the Cos Θ = 1 and for the destructive interference the value of  Θ = 90°, so that the Cos Θ = 0.

In case of the incoherent sources or waves we can the intensity simply by algebraic method that means I = I1 + I2.

Watch the video below for detailed derivation

### EFFECT OF DIELECTRIC IN A CAPACITOR

The capacitance of a parallel plate capacitor without any medium between its plates is given by $C_{0}=\frac{\varepsilon _{0}A}{d}$

When a dielectric completely fills the space between the plates of the capacitor, the capacitance increases K times, where K is the dielectric constant (relative permitivity) of the dielectric.

$C_{m}=\frac{K\varepsilon _{0}A}{d}$

If a dielectric slab of thickness t (<d) is introduced between the plates, the capacitance becomes $C=\frac{\varepsilon _{0}A}{d-t\left ( 1-\frac{1}{K} \right )}$

OR

$C=\frac{\varepsilon _{0}A}{d\left \{ \frac{t}{d}\left ( 1-\frac{1}{K} \right ) \right \}}$

OR

$C=\frac{C_{0}}{\frac{t}{d}\left ( 1-\frac{1}{K} \right )}$

In each case the capacitance increases with the introduction of a dielectric in between the plates

http://teacher.pas.rochester.edu/phy122/Lecture_Notes/Chapter27/chapter27.html

## Sunday, October 9, 2011

### Friction Problem

Two masses M1 and M2 are connected by a light rod and the system is slipping down a rough incline of angle theta with the horizontal. The frictional coefficiant at both the contacts is u fhnd the accelaration of the system and the force by the rod on one of the blocks.

Friction problem from h.c verma

## Friday, October 7, 2011

### A Numerical Problem from Kinematics

A car starts motion from rest at uniform acceleration of 2m/sec 2 for 3 seconds, and then it maintains a constant speed for 2 seconds.Then the breaks are used to decelerate the car uniformly to rest during a time of 3 seconds.

Draw the graph representing the journey of the car then calculate

1)the maximum speed in km/sec
2)the total displacement covered

(Ahmed sent this problem)

## Monday, October 3, 2011

### HC Verma Solutions

I want H C Verma solution of chapter 3 & 8. I cannot solve  H C Verma problem because it is difficult for me. But i want to it. Please give some idea to solve  H C Verma. My basic concept is not clear. (Komal Posted)

The solutions to HC Verma's Concepts of Physics - all chapters are already available at this site. If you have any specific doubts, you can ask quoting the particular question in full.

## Sunday, October 2, 2011

### CBSE AISSCE AISSE syllabus and text book in pdf for download

Yogeswaran posted: "im searching AISSCE books in CBSE syllabus by Pdf i want to download it"

Dear students, The text books used by CBSE schools are the NCERT Textbooks. They are available for download (FREE) at the ncert website. I am providing the links for easy access.

Please note that the books are in pdf form and the different chapters are zipped. You have to download the zipped file and then extract the zipped files. You can use them for personal use. But copyright prohibits the unauthorized printing for any commercial purpose.