July 18, 2018

XI Physics | Dot Product Solved Numericals


Q.15 Find the angle between A=2i + 2j – k and B=6i – 3j +2k. Q.16 Find the projection of the vector A= i – 2j + k on to the direction of vector B=4i – 4j +7k Q. 17 Find the angles alpha, beta and gamma which the vector A=3i – 6j +2k makes with the positive x,y,z axis respectively. Q.18 Find the work done in moving an object along a vector r=3i – 2j +5k is the applied force is F=2i – j – k. Q.19 Find the work done by a force 30,000 N in moving an object through a distance of 45 m when :(a) force is in the direction of motion;(b) force makes an angle of 40 degrees to the direction of motion.Find the rate at which the force is working at a time when the velocity is 2 m/s. Q.20 Two vectors A and B such that |A|=3, |B|=4 and A. B=-5 , find (a) The angle between A and B. (b) The Length |A+B| and |A-B| (c) The angle between (A+B) and (A-B)

July 16, 2018

Definition of Henry

Frequently asked questions about Henry:

1. What is the definition of Henry in Physics?
2. What is the definition of Henry in Electromagnetic induction?
3. Henry is the unit of?
4. What is Henry?
5. One Henry is equal to?

Answer:

Definition of Henry in terms of Self Inductance:-

            Henry is the S.I. Unit of Self Inductance."The self inductance of a coil is 1 Henry if the current varying through it at the rate of 1 ampere per second induces a back emf of 1 volt."

Definition of Henry in terms of Mutual Inductance:-

Henry is also the S.I. Unit of Mutual Inductance."The mutual inductance of a coil is 1 Henry if the current varying through primary coil at the rate of 1 ampere per second induces a back emf in secondary coil of 1 volt."

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July 14, 2018

How To Survive An Elephant Attack








The Concept applied is " Inertia"...

Inertia:

Everybody in this universe has a property that it always offers some resistance to the change of its state. This property is known as Inertia and it is because of the mass of body. Therefore we need force to overcome inertia for the change of its state, either rest or motion.

July 05, 2018

X Lecture No.3 | Physical Quantities




Do you know ?

1. How long is One meter?
2. One Second is how long duration?
3. One kilogram is the mass of which object?
4. Which quantities are measured in Physics and Which are not measured in Physics?

This Lecture Includes:

1. Physical and Non Physical Quantities
2. Basic / Fundamental Quantities
3. Derived Quantities with examples
4. Conversions of length , mass and time.

June 30, 2018

Why The Color Of Sky Is Blue


When the sun's light reaches the Earth's atmosphere it is scattered, or deflected, by the tiny molecules of gas (mostly nitrogen and oxygen) in the air. Because these molecules are much smaller than the wavelength of visible light, the amount of scattering depends on the wavelength.

Shorter wavelengths (violet and blue) are scattered the most strongly, so more of the blue light is scattered towards our eyes than the other colours. You might wonder why the sky doesn't actually look purple, since violet light is scattered even more strongly than blue. This is because there isn't as much violet in sunlight to start with, and our eyes are much more sensitive to blue.

The blue light that gives the sky its color, is sufficiently bright to make all the stars that we see at night disappear since the light they emit is much dimmer.

June 21, 2018

XI Lecture No.3 | Significant Figures

Lecture Includes: XI Chapter No.1 : The Scope of Physics 1. Introduction to Significant Figures 2. Rules for counting Significant Figures 3. Examples of Significant Figures Previous Lectures: XI Lecture No.1|Introduction,History and Muslim Contribution: https://youtu.be/4tmmM3Hg5EU XI Lecture 2| Dimensions : https://youtu.be/svzZ2fUS__8

June 14, 2018

XI Physics | Solved Numericals | Chapter No.1 | The Scope of Physics



XI Physics Chapter No.1 : The Scope of Physics

1. Find the area of rectangular plate having length (21.3 +/- 0.2 ) cm and width (9.80 +/-0.10) cm.

2.Calculate (a) the circumference of circle of radius 3.5 cm. and (b) area of circle of radius 4.65 cm.

3.Prove that S=vit + 1/2 at^2 is correct dimensionally.

4.Suppose displace of a particle is related to a time according to a expression S= ct^3. what are the dimensions of constant c ?

5.Estimate the number of liters of gasoline used by all Pakistan's car each year.

June 08, 2018

XI Lecture 2| Dimensions



Chapter No.1 : The Scope of Physics
Topic :Dimension

Lecture contents:
1. Definition of Dimension
2.Dimension of Physical Quantities
3.Equation verification by using dimensions and Exam Questions

June 07, 2018

XI Lecture No.1 The Scope of Physics






Chapter No.1 : The Scope of Physics
Lecture contains;
1. Introduction and definition of Physics
2. Brief History of Physics
3. Contribution of Islamic World towards Science

May 31, 2018

Interpret velocity-time graph for constant direction and understand significance of area under velocity-time graph.

VELOCITY-TIME GRAPH FOR CONSTANT DIRECTION:
When an object is moving with a constant velocity, the line on the graph is horizontal. When an object is moving with a steadily increasing velocity, or a steadily decreasing velocity, the line on the graph is straight, but sloped. The diagram shows some typical lines on a velocity-time graph.

The steeper the line, the more rapidly the velocity of the object is changing. The blue line is steeper than the red line because it represents an object that is increasing in velocity much more quickly than the one represented by the red line.
Notice that the part of the red line between 7 and 10 seconds is a line sloping downwards (with a negative gradient). This represents an object that is steadily slowing down.
AREA UNDER VELOCITY-TIME GRAPH:
            Study this velocity-time graph.
The area under the line in a velocity-time graph represents the distance travelled. To find the distance travelled in the graph above, we need to find the area of the light-gray triangle and the dark-gray rectangle.
1.    Area of light-gray triangle
o    The width of the triangle is 4 seconds and the height is 8 metres per second. To find the area, you use the equation:
o    area of triangle = 12 × base × height
o    so the area of the light-gray triangle is 12 × 8 × 4 = 16 m.
2.    Area of dark-gray rectangle
o    The width of the rectangle is 6 seconds and the height is 8 metres per second. So the area is 8 × 6 = 48 m.
3.    Area under the whole graph
o    The area of the light-gray triangle plus the area of the dark-gray rectangle is:
o    16 + 48 = 64 m
o    This is the total area under the distance-time graph. This area represents the distance covered.
Summary
·         The gradient of a velocity-time graph represents the acceleration
The area under a velocity-time graph represents the distance covered

May 12, 2018

Derivation of Gravitational Potential Energy (without using Calculus)

The potential energy of a body at height “h” from centre of earth w.r.t. a point at which the gravitational field is zero i.e. a point which has no potential is called absolute gravitational potential energy.




Where RE is the radius of earth.The minus sign indicates that the potential energy is “negative” at any finite distance that is the potential energy is zero at infinity and decreases as the separation distance decreases. This is due to the fact that the gravitational force acting on the particle by earth is attractive. As the particle moves in from infinity the Work is positive which means U is negative.


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”.