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### Generation Alzheimer’s: The Defining Disease of the Baby Boomers

This year, the first of the Boomer Generation turns 65 and with increased age comes increased risk of developing Alzheimer's disease. To bring urgently-needed attention to the risk facing the Boomers, the Alzheimer's Association recently released a groundbreaking study titled, Generation Alzheimer's: The Defining Disease of the Baby Boomers.

"Alzheimer’s is a tragic epidemic that has no survivors. Not a single one," said Harry Johns, president and CEO of the Alzheimer’s Association. "It is as much a thief as a killer. Starting this year, more than 10,000 baby boomers a day will turn 65. As these baby boomers age, one of out of eight of them will develop Alzheimer’s – a devastating, costly, heartbreaking disease. Increasingly for these baby boomers, it will no longer be their grandparents and parents who have Alzheimer’s – it will be them. It is estimated that 10 million baby boomers will end up developing Alzheimer's Disease.

In addition to the human toll, over the next 40 years Alzheimer’s will cost the nation $20 trillion, enough to pay off the national debt and still send a$20,000 check to every man, woman and child in America. And while every 69 seconds someone in America develops Alzheimer’s disease today, by 2050 someone will develop the disease every 33 seconds - unless the federal government commits to changing the Alzheimer’s trajectory.

Generation Alzheimer's: The Defining Disease of the Baby Boomers, sheds light on a crisis that is no longer emerging – but here. If you’d like to view a full copy of this report please visit

The Alzheimer's Association is the world’s leading voluntary health organization in Alzheimer’s care, support and research. Our mission is to eliminate Alzheimer’s disease through the advancement of research; to provide and enhance care and support for all affected; and to reduce the risk of dementia through the promotion of brain heal

Hi all,
All of us have problems in a subject like physics . So I invite you all to send me your queries at any of my mail address mailmephysics12@rediffmail.com or at physicsexpert12@gmail.com . I would try my best to solve your queries and would post them on my blog. If you have anything you want to share (related to physics, mathematics, chemistry, managing competitions etc.) with visitors of my blog feel free to mail me your article along with your link.
thanks
physics expert

### Magnetic force on charged particle in a magnetic field

Question: Describe the magnetic force on the particle if it is at rest; it moves along  the direction of the magnetic field; it moves opposite the direction of the magnetic field; and if its at right angle with the direction of the magnetic field.

1. In a magnetic field B, a particle of charge q and velocit v experiences a force,
F = q(v X B)
If v = 0, the F = 0 and hence the particle experiences no force.
(Here, bold letters represent vectors)
2. if the particle moves in the direction of the field then F=qvBsin(0) = 0 again particle does not experience any force when it move parallel to the magnetic field.
3. Again F=0 for the case when particle moves in a direction opposite to the field as
F=qvBsin(180) = 0 since the angle between and is 180 degree.
4. In case and are both perpendicular to each other then charged particle will follow the circular path .

### Rigid Body Rotation Question 1

Question:
A rigid body of radius of gyration k, mass m and radius R rolls without slipping down a plane inclined at an angle θ  with the horizontal. (a) Find its acceleration and frictional force acting on it . (b) If the body were in the form of a disc and θ=30º , what will be the acceleration and the frictional force acting on it.

Solution:

### conceptual physics Centripital force

Hi all
I came across this video while browsing you tube and i like the way it explains about what is the concept of centripetal force.

### How to calculate the direction of induced emf : Lenz's law

• The direction of induced current and emf is given by lenz's law.
• Due to change in magnetic flux through a closed loop an induced  current is established in the loop.
• Lenz's law states that
'The induced current due to the induced emf always flow in such a direction as to oppose the change causing it'
• Now we can combine faraday's law  to find the direction of emf.
• Thus we can say that "The emf induced in a coil is equal to the negative rate of the change of the magnetic flux linked with it "

Explaination of lenz's law

• To explain this law again consider faradays experiment 1 in which north pole of the magnet  moves towards a closed coil.
• This movement of north pole of magnetic induces current in the coil in such a direction so that end of the coil ,facing and approaching north pole becomes a magnetic north pole.
• The repulsion between two poles opposes the motion of the magnet towards the coil.
• Thus work has to be done to push the magnet against  the coil.
• It is this mechanical work which causes the current to flow in the coil against its resistance R and supply
the energy for the heat loss.
• The mechanical workdone is converted to electrical energy which produces the heat energy.
• If the direction of the induced current were such as not to oppsose the motion ,then we would be obtaining electrical energy continuously without doing any work ,which is impossible.
• So ,every things seems to be all right if we accept lenz's law otherwise the principle of conservation of the
energy would be violated.
• Direction of the induced current can be found using Fleming right hand rule.
" If we stretch thumb ,index  and middle finger  perpendicular to one another then index fingers points in direction of the magnetic field ,middle finger in direction of induced current and thum points in direction of the motion of the conductor"

### Optics subjective question 1

Question
A narrow monochromatic beam of light of intensity I is incident on a glass plate A as shown below in the figure

Another identical glass plate B is kept close to A  and parallel to it. Each glass plate reflects 25% of the light intensity incident on it and transmits the remaining.Find the ratio of maximum and minimum intensities in the interference pattern formed by the two beams obtained after reflection from each plate.

Solution:
Hi First try to solve the question on your own it's an easy one . The answer is ratio of intensities is 49. I will provide the solution to this question.

### PN junction

• P-N junction is the basic building block of many semiconductor devices like diodes transistors etc.
• An P-N junction is formed when a P-type semiconductor is joined to a N-type semiconductor in such a way that the crystal structure remains continuous at the boundary.
• Three basic processes used for preparation of an P-N junction are alloying , growing and diffusion out of which diffusion is generally used for the preparation of an P-N junction.
• One very important characteristic of an P-N junction is its ability to conduct current only in one direction and the very high resistance it offers in another (or reverse direction).
• Consider the figure given below which shows a simple P-N junction having P type material towards left hand hand side and N-type material towards right hand side.

• P-type material have high concentration of holes and N-type material has high concentration of electrons. Along with these majority charge carriers both type of materials also consists of few minority charge carriers.
• As soon as P-N junction is formed holes begin to diffuse from P region to N region and electrons begin to diffuse from N region to P region and electron and holes begin to recombine in pairs.
• Due to diffusion and recombination of electrons and holes there remain no charge carriers near junction and this region known as depletion region is formed on both sides of the junction as shown in the figure.
• The thickness of this depletion region is of the order of one-tenth of micrometer.
• In depletion region there are stationary negative ions towards P side and positive ions towards N side.
• This creates a potential difference between two parts of the junction where N region is at higher potential with respect to P region .
• An electric field thus develops in this depletion region  which is directed from positive charged ions in N region towards negative charged ions in P region.
• Under the influence of this field electrons which are minority charged carriers in P side of the junction moves to N side and holes on N side of the junction moves to the P side.
• The motion of charged carriers due to this electric field is called drift.
• This internal electric field helping the movement of minority charged carriers adjust itself in such a way that drift of minority charged carriers across the junction is counterbalanced by the diffusion of same number of majority charged carriers across the junction thereby creating a state of equilibrium.

### Phasor digrams

• Phasor diagrams are the diagrams representing alternating current and voltage of same frequency as vectors or phasors with phase angle between them.
• Phasors are the arrows rotating in the anti-clockwise direction i.e., they are rotating vectors but they represent scalar quantities.
• Thus alternatinc current and voltage varying sinusoidally can be represented by anticlockwise rotating vectors if they satisfy following conditions
(i) length of the vector must be equal to the peak value of alternating voltage or current.
(ii) vector representing alternating current and voltage would be at horizontal position at the instant when alternating quantity is zero.
• In certain circuits when current reaches its maximum value after emf becomes maximum then current is said to lag behind emf.
• When current reaches its maximum value before emf reaches its maximum value then current is said ti lead the emf.
• Figure given below shows the current lagging behind the emf by 90 degree.

### Numerical for class 12 on electric field and potential

Question:
A thin stationary ring of 1 m has a positive charge of 1 x 10-5C uniformly distributed over it. A particle of mass 0.9 gm and having a negative charge of 1 x 10-6 C is placed on the axis at a distance 1 cm from the center of the ring. Show that the motion of the negatively charged particle is approximately simple harmonic. Calculate the time period of oscillation.

Solution:

### What are Dielectrics

• A dielectric is an insulating material in which all nuclei are tightly bound to the nuclei of the atom.
• There are no free electrons in a dielectric material so they can not carry current.
• Electric conductivity of a dielectric material is very low and that of an ideal dielectric is zero.
• Some examples of dielectric materials are glass, plastic, mica, oil etc.
• Dielectric constant of a material is the ratio of the capacitance of the capacitor completely filled with the material to the capacitance of the same capacitor in the vacuum i.e. dielectric constant K=C/C0.
• If the space between a capacitor is filled with a dielectric material capacitance of the capacitor increases.
• The value of dielectric constant K is independent of the shape and size of the capacitor and its value is different for different insulating materials.

### Problem solving tricks-Right hand rules (Magnetic fields due to currents)

Right hand rule for cross product:-
Consider that c is the cross product of two vectors a and b i.e.,
c=a x b
If direction of vector a is along the x axis and that of b along z axis then direction of vector c could be find using right hand rule for cross products. With the thumb, index, and middle fingers at right angles to each other the first (index) finger can represent a, the first vector in the product; the second (middle) finger, b, the second vector; and the thumb, c, the product. So direction of vector c is perpendicular to the plane containing vectors a and b. This rule can be used in determining the directions of torque and angular momentum vectors and also to find the direction of the force on current carrying wire in an magnetic field.

Right hand thumb rule:-
This rule is used in situations when rotation is specified by a vector and we need to relate a curled element and a straight element , many such situations arises when you study magnetism. This can be done when you curl your fingers and straighten the thumb of your right hand. As an example you can consider an electric current passes through a straight wire. Here, the thumb points in the direction of the conventional current (from positive to negative), and the fingers point in the direction of the magnetic lines of flux.

### Kinematics problem

Question
A car accelerates from rest at a constant rate p for some time after which it decelerates at a constant rate q to come to rest. If total time lapse is t, find (1) the maximum velocity attained and (2) the total distance traveled.

Solution

### Solved question on Structure of atom and Bohr atom model

Question:
Suppose that the potential energy between an electron and a proton at a distance r is given by -ke2/3r2 . Use Bohr theory to obtain energy level of such a hypothetical hydrogen atom.

Solution:

### CAPACITOR question with solution (Difficulty level : easy one)

Question-1:A Parallel Plate capacitor has following dimensions
Distance between the plates=10 cm
Area of Plate=2 m2
Charge on each plate=8.85 x 10-10 C
Calculate following
1. Electric Field outside the plates
2. Electric Field Between the plates
3. Capacitance of the capacitor
4. Energy stored in the capacitor
ε0=8.854 x 10-12 C2N-1m-2
Solution-1:

As we know that Electric field outside the plates are zero
Electric field Inside the plates is
E=Q/ε0A =50NC-1

Capacitance=ε0A/d =8.854 x 10-12  x 2/.1=17.6 x 10-11 F

Energy stored in capacitor=(1/2)Q2/C=.5 x 8.85 x 10-10 x 8.85 x 10-10/17.6 x 10-11
=22.125 x 10-10 J

### Inertial and non inertial frames

• Both rest and motion are relative terms and there is nothing like absolute rest or absolute motion.
• Position or state of motion of a body may appear different in different frame of reference i.e.,  an object at rest in one frame of reference might appear to be in motion in another frame of reference.
• Newton's first law of motion also known as law if inertia does not always holds for all frame of reference and the frames in which this law holds good are called inertial frames of reference.
• Inertial frames of reference are non-accelerating frames this means that either they are fixed or move with constant velocity.
•  Non-inertial frames are the frames in which newton's law of inertia does not holds true.
• Rotating and acceleration frame of references falls in the category of non inertial frames.
• In this frame acceleration is caused by fictitious or pseudo forces.
For more or full notes on kinematics visit this link

### Hydrostatics question

Question
T what height h should a cylinder vessel of radius r be filled with a homogeneous liquid of density  to make the force , with which the liquid presses on the sides of the vessel equal to the force exerted by the liquid on the bottom of the vessel.

Solution

### A question on Gauss's law

Question : A spherical liquid drop of radius r has charge q. If n number of such drops coalesces to form a single bigger drop , then on the surface of bigger drop what is
(1) charge
(2) charge density
(3) electric field and
(4) potential

This question is quite a easy one try and solve it though I'll provide the solution of this question.

### Subjective Question Archive

Hi all,
I have given the link of most of the subjective questions in this blog under the tab "Subjective Question Archive" please visit the page and i hope you will definitely learn something or the other about solving questions in various topics in physics while going through these questions. Most of the questions given came along with their answers and solutions .
Hope you like the page
With best wishes for your exams
Physics Expert

1. The generation of A.C. is cheaper than that of D.C.
2. A.C. machines are simple , robust and do mot require much attention for their repairs and maintainance during their use.
3. Wide range of voltages are obtained by the use of transformer.
4. The magnitude of current can be reduced by using an inductance or a conductor without any appreciable loss of energy
5. A.C. can easily be converted into D.C. with the help of rectifiers.
6. When A.C. is supplied at higher voltages in long distance transmission , the line losses are small compared to a D.C. transmission

1. Peak value of A.C. is high and it is dangerous to use so better insulation is required.
2. It attracts person who touches it unlike D.C. which gives a repelling shock.
3. An A.C. is transmitted from surface of the conductor and hence need several strands of thin wires insulated from each other.

### Physics for IIT-JEE,AIEEE ,PMT and Board examinations ,IIT-JEE Learning Material, IIT Preparation , IITJEE/AIEEE Test Series,IITJEE Online Study Material, Online Test Series, Online Coaching,Board Examination

For full note on various chapters in physics visit
Physics study material for iitjee, aieee, pmt and board examination

### PMT Focus : Assertion reason type questions

The following questions consists of two statements , Assertion and Reason. While answering these questions choose any of the following four responses
A. If both assertion and reason are true and the reason is correct explanation of assertion.
B. If both assertion and reason are true but reason is not a correct explanation of assertion.
C. If assertion is true and reason is false.
D. If both assertion and reason are false.

1. Assertion : In series LCR circuit , resonance occurs only at one frequency.
Reason :  At this frequency inductive reactance is equal to capacitive reactance.
(a) A
(b) B
(c) C
(d) D

2. Assertion: Insulators do not allow the flow of current through themselves.
Reason: They have no free charge carriers.

(a) A
(b) B
(c) C
(d) D

3. Assertion : When temperature of cold junction of a thermocouple is lowered , the value of neutral temperature of this thermocouple is raised
Reason : When the difference of temperature of two junction is raised , more thermo e.m.f. is produced.

(a) A
(b) B
(c) C
(d) D

4. Assertion : If two parallel wires , hanging freely are connected to a battery in series , they come closer to each other.
Reason : Force of attraction acts between two wires crying charge

(a) A
(b) B
(c) C
(d) D

5. Assertion : If an electron and proton enter an electric field with equal energy , then path of electron is more curved then that of electron.
Reason : electrons has a tendency to form curve.

(a) A
(b) B
(c) C
(d) D

1. a
2. a
3. d  here both assertion and reason are not true
4. d when two long parallel wires are connected to battery in series they carry current in opposite direction and hence repel each other.
5. d

### Surface tension fact file

1. Those factors which increases cohessive forces between liquid molecules increases surface tension and those decreases cohesive forces decreases surface tension.
2. If impurity is completely soluble , then on mixing it in the liquid , its surface tension increases.
3. With the increase in temperature surface tension decreases.
4. Surface tension depands on the medium present on other side of the liquid surface.
5. The surface tension decreases due to electrification.
6. On mixing partial soluble impurities in a liquid , its surface tension decreases like mixing of detergent in water decreases surface tension of water.

### Challenging mechanics problem : Kinematics

Question :
A body of mass m rests on horizontal table which has coefficient of static friction μ . It is desired to move the body by applying minimum possible force F. Find the magnitude and direction of the force F to which it has to be applied.
Solution :

### Problem on Bohr atom model

Question:
A particle of charge equal to that of electron and mass 208 times the mass of electron (-meson)moves in a circular orbit around a nucleus of charge +3e (assume mass of nucleus to be infinite). Assuming that the Bohr atom model is applicable to this system
(a) derive an expression for the radius of the nth Bohr orbit
(b) find the value of n for which the radius of the orbit is approximately the same as that of the first Bohr orbit for the hydrogen atom
(c) find the wavelength of the radiation emitted when  -meson jumps from the third orbit to the first orbit (Rydberg constant = 1.097 x 107 m-1)

Solution: