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Free ebook Download (Electric Current, Resistance and Resistivity revision notes pdf)

2012-01-30T00:11:00.000-08:00

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Electric Current, Resistance and Resistivity revision notes pdf is now available for free download from physicscatalyst.com
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Time management tips for students

2012-01-29T04:11:00.000-08:00

1) Prepare a Schedule/Calendar for the studies.You only have 24 hours a day, 168 hours a week . Effective study time management means that you use your given time in the most efficient way. Therefore it is important to prepare a regularly updated schedule/calendar, where you:

a) write down all your scheduled tests

b) write down all tasks, assignments and duties,

c) record your planned leisure-activities, such as gym, etc.

d) Write an ordered list of what you need to get done.Prioritize the items on your list.

2) Study time management: Take yourself some minutes after coming home from school and evaluate the amount of time you can invest for your studies. This is where you start to manage your study time, so I would recommend you to take up to 15 minutes for this! Make sure to include time for studying, completing tasks and assignments, projects, etc.

3)One of the best things you can do to manage your time (then be managed by it) is to learn to say “no.” Say “no” to people asking you to play pool when you should study or when someone wants help with something at an inconvenient time for you. Suggest a different time to help when it’s more convenient for you.

Remember that there’s a time for everything. Sure, studying for a long time is good, but take breaks. Take power naps when your brain starts frying. If the weather’s nice, a good game of ultimate Frisbee also refreshes the tired mind.

4) Another every important study time management technique is to schedule your time dependent on your personal energy level. Your energy level reaches its peak at approximately 7am, but is very low during the time from 3pm to 5pm.A lot of students are very productive in the morning, so it could be very useful to rise up early . Others prefer the evening hours as their most productive part of the day. The only important thing is that you know for yourself on which time-period you can work most efficient and adapt your schedule accordingly to your high-energy periods.

5) Procrastination: One of the biggest obstacles you might face while applying effective study time management is procrastination, which is correlated to discipline. Every student is affected by procrastination once in a while or continuously. The desire to avoid specific tasks comes within boredom, fear or similar concerns. Not getting started will lead to stress and anxiety, which are very negative emotions during your studies. Luckily you can overcome procrastination by applying the following study time management technique: create smaller sub goals and sub tasks. You will notice that a sub task will help you to get started with your studies and will get you motivated to do the next tasks as well.

6) Get the most out of class. Go to class and be on time. Be well-prepared and ready for discussion.

FREE Physics study material (notes and questions)

2012-01-28T01:54:00.000-08:00

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2012-01-17T21:35:00.001-08:00

Our New Free physics ebooks (pdfs) are available at this link . Hope you lile them.

Electric and Magnetic Fields

2012-01-13T03:32:00.000-08:00

We will now discuss electric and magnetic field vectors (E and B)at a point in the absence of charge.
Now let us place a charge q at point (x,y,z) in space. If this charge experiences a force as given by Lorentz force equation then we can associate vectors E and B with this point (x,y,z) in space.
Thus at any time t vectors E(x,y,z,t) and B(x,y,z,t) gives forces experienced by any charge q at point (x,y,z) with a condition that placing this charge at point (x,y,z) in space does not disturb the position or motion of all other charges responsible for the generation of the field.
So, every point in space is associated with vector E and B which are functions of x,y,z and t.
Since E(or B) can be specified at every point in space , we call it a field.
A field is that physicsl quantity which takes on different values at different points in space for example velocity field of a flowing liquid.
Electromagnetic fields as we know are produced by complex formulas but the relationships between values of the fields at one point and the values of the feld at neighbour points are vary simple and can form differential equations which can completely describe the field.
To understand and visualize the behaviour of field we can consider the field as a function of position and
time. We can also create a mental picture of field by drawing the vectors at many points in space each of which gives strength and direction of field at that point.
Flux is one property of field and flux of a vector field through a surface is defined as the average value of normal component of the vector times the area of the surface.
Another property is the circulation of the vector field and for any vector field circulation around any imagined closed curve is defined as the average tangential component of the vector multiplied by the circumfrance of the loop.
With just the idea of flux and circulation we can define all the laws of electricity and magnetism.

Refrence:- The Feynman lectures on physics Vol 2

Galilean Transformation

2012-01-13T03:26:00.001-08:00

Motion is a relative concept . You are sitting on a train. A object on trains seems to be at rest from your perspective but it is in motion from the person standing on the ground.So it is tied to particular frame of refrence choosen by observer.

Now Different observer may use different frame of refrence , And velocity ,acceleration may be different from these different frame of refrence

It is important to know how these measurement in different frame of refrence are related.

For two observer S₁ and S₂ who move relative to each other with rectilinear motion, The velocity,displacement and acceleration of an object measured from these two observer are related as

r₂=r₁ -R

Where r₁ is the position vector of object from observer S₁ and r₂ is the position vector of object from observer S₂. R is the position of observer S₂ from S₁

v₂=v₁ -v

Where v₁ is the velocity of object relative to observer S₁ and v₂ is the velocity of object relative to observer S₂. v is the velocity S₂ relative to S₁

a₂=a₁ -a

Where a₁ is the acceleration of object relative to observer S₁ and a₂ is the acceleration of object relative to observer S₂. a is the acceleration S₂relative to S₁

When the two observer are moving in uniform relative translation motion with velocity v and t=0 when the observer were coincident,these equation becomes

r₂=r₁ -vt

v₂=v₁ -v

a₂=a₁

t₁=t₂

The above equation are called Galilean transformation of coordinates ,velocities and accelerations

So acceleration of the object remains same for all observer in uniform relative translational motion

Law of Radioactive decay

2012-01-13T03:20:00.001-08:00

Radioactivity is a nuclear phenomenon
When a nucleus disintegrates by emitting a particle ( α and β) or by capturing an electron from the atomic shell( K-shell) ,the process is called radioactive decay. This decay process is spontaneous.
Let us take a radioactive sample containing N₀ at time t=0 i.e, at the beginning. We wish to calculate the number N of these nuclei left after time t.
The number of nuclei of a given radioactive sample disintegrating per sec is called the activity of that sample is
dN/dt=rate of decrease of nuclei with time=Activity of sample at time t --(1)
Experimentally it is found that the activity at any instant of time t is directly proportional to the number N of parent type nuclei present at that time

Where λ > 0 is proportionality constant and negative sign indicates that N decreases as t increases
From equation (2) we get

i.e. ,λ is fractional change in N per sec
=> λ is not merely a proportionality constant ,but it gives us the probability of decay per unit interval of time
Hence λ is called the probability constant or decay constant or disintegration constant
dN is the no of parent nuclei that decay between t and t+dt and we have taken N as continuous variable
From (2)

N₀=No of radioactive nuclei at t=0
From (4) we see that law of radioactive decay is exponential in character
From figure it can be noted that only half the amount of radon present initially after 3.83 days and 1/4 after 7.66 days and so on
Plot shows that in a fixed time interval a fixed fraction of the amount of radioactive substance at the beginning of interval decays
This faction is independent of the amount of radioactive substance and depends only on the interval of the time
The decay constant λ is a characteristics of radioactive substance and it depends in no way on the amount of the substance present

What are black holes

2011-12-24T22:52:00.000-08:00

According to special theory of relativity, the maximum velocity that can exist is the velocity of light
c=3X10⁸ m/s
Now we also Know that escape velocity which is the velocity needed for an object to become essentially free of the gravitational effect of another object is given

v = \sqrt{\frac{2 GM}{R}}

v^{2} = \frac{2 GM}{R}

We may speculate on the mass and radius of a steller body that has an escape velocity of c.
Then

c^{2} = \frac{2 GM}{R}

R = \frac{2 GM}{c^{2}}

This quantity R is called the Schwarzschild Radius and is usually designated by R_S
Substituting the values of G and c,we have
R_S=1.485 X10^-2 M
The above equation gives us the relation between M and R_S. It states that A body of Mass M in kg and radius R_S in m or smaller produces such a strong gravtitional at its surface that no particle on its surface can escape.This even applied to electromagnetic radiation ( photons) including light.
So Even light cannot escape from such planet or body. That is the reason such body bodies are termed as Black holes
The most common way for a black hole to form is probably in a supernova, an exploding star. When a star with about 25 times the mass of the Sun ends its life, it explodes. The outer part of the star screams outward at high speed, but the inner part of the star, its core, collapses down. If there is enough mass, the gravity of the collapsing core will compress it so much that it can become a black hole. When it’s all over, the black hole will have a few times the mass of the Sun. This is called a “stellar-mass black hole”, what many astronomers think of as a “regular” black hole.

Fictitous Force and Free falling Elevator

2011-12-24T22:49:00.001-08:00

A non inertial Frame of Refrence is the frame of refrence which is having acceleration(a₀) Example Free Falling elevator

Newtons law are valid in inertial frame of refrence only. We cannot apply them as it is in non inertial frame of refrence as it left out the acceleration of the object because of the frame of refrence.

Let me provide simple example to illustrate this.

You are moving in car which is accelerating. From your frame of refrence,a block on the road would be accelerating in opposite direction.

Now if we apply newton's law, we will find acceleration to be zero as no net force is acting. But the block has acceleration from car frame of refrence.

So to fix this issue,we will add one fictitous quantity in the Newton law equation like

F+F₀=Ma

Where F₀ is the fictitous force and it is in opposite direction of accleration frame

F₀=-Ma₀

Where a₀is the acceleration of Non inertial frame of refrence

Now let me further illustrate this with example of free falling elevator

A free falling elevator is an non inertial frame of refrence.The acceleration of the elevator as defined from the observer on the ground will be

g=-gk

Where k is the unit vector along vertical axis in the upward direction

Let us take an unattached object of mass M in the elevator.

From the frame of refrence of free falling elevator,Two forces are acting on the mass

Fictitous Force due to non inertail frame of refrence

F_fic=Mgk It is opposite to the acceleration of the elevator

Gravitional Force on the Mass

F_G=-Mgk

So the total Force on the body from elevator frame of refrence

F_T=F_fic+F_G=0

Which mean body is unacclerated in the elevator frame of refrence. The body will appear to be suspended in the air ,if it has no initial relative velocity to the elevator

Few more important things about Fictitous force

Fictitous force are called pseudo force.
It simple represent the effect of the acceleration of the non inertial frame of refrence
They dont have any physical significance
Whenever we work the problem in non inertial frame of refrence,always make sure to include fictitous force in the newton law

Different type of Force and their origin

2011-12-07T21:58:00.000-08:00

A) Normal Force: When we put a book on a table ,the molecules of the book exert downward forces on the molecules of the table.The molecules composing the upper layer of the tabletop move downward until the repulsion of the molecules below balances the forces applied by the book.
This compression always occur but it is too slight to notice
The following things are good to notice about normal force
a) For a body resting on a surface,Normal force is equal and opposite to the resultant of all the other forces which acts on the body in the direction perpendicular to surface
b) Weight and Normal force are not action reaction pair as they act on same body whereas action -reaction acts on different body

B) Tension: Tension usually comes under picture for string and rope. The string can be think of small short sections interacting by contact forces
Each section pulls the section to either side of it and by Newton third law,it is pulled by the adjacent section. The magnitude of the forces acting between the section is called Tension
The Following things are good to notice about tension
a) If the tension is uniform,the net string force on each small section is zero and section remains at rest
b) if the string is accelerating ,the tension generally varies along the string
c) If there is external force on the string then also tension varies along the string

C) Friction Force: Friction force generally comes into picture when one body moves or tries to move along the surface of the second body
Friction always opposes the motion which would occur in its absence. Friction occurs becuase of interatomic forces at the actual area of contact on atomic scale.
a) When we try to push a box on the table, if we push the box gently ,the box remains at rest. Force of friction assumes a value equal to the force applied by us. The force of friction cannot increase indefinately. If we push the box hard,the box start to slide

D) Viscous Forces: A body moving through liquid or gas is retarted by the force of viscosity exerted on it by fluid. It arised because a body moving through the medium exerts forces which set the nearby fluid into motion.By newton third law,the fluid exerts a reaction force on the body
The Following things are good to notice about viscosity
a)Viscous forces are proportional to velocity
b) It always retard the motion

Polarization by reflection

2011-11-29T22:08:00.001-08:00

This simple method of obtaining plane polarized light by reflection was discovered by malus in 1808
We found that when a beam of light is reflected from the surface of a transparent medium like glass or water, the reflected light is partially polarized and degree of the polarization varies with angle of incidence
The percentage of polarized light is greatest in reflected beam when light beam is incident on the transparent medium with an incident angle equal to the angle of polarization
For ordinary glass with refractive index =1.52 ,angle of polarization is 57.5⁰
Figure below shows the polarization of light by reflection
we can use a Polaroid as an analyzer to show that reflected light is plane polarized . we rather say that reflected light is partially plane polarized
the examination of transmitted light shows the variation in intensity indicating that the light is partially polarized
The vibrations of this plane polarized reflected light are found to be perpendicular to the plane of incidence and therefore ,the reflected light is said to be plane polarized in the plane of incidence

Kinematics Question

2011-11-26T22:15:00.001-08:00

Question:

A ball of mass 100 g is projected vertically upward from the ground with avelocity of 49m/s. At the same time another identical ball is dropped from aheight of 98 m to fall freely along the same path as followed by the firstball. After some time ,the two balls collide and stick together and finallyfall together .

g=9.8m/s²

i is the unit vector along upward direction

1) Find the time at which balls collide in air

a) 2.1 sec

b) 1.2 sec

c)1 sec

d) 2 sec

2) Find the velocity vector of the combined mass just after collision

a) 4.8i

b) 3i

c)-4.9i

d) 4.9i

3) Find the time of the flight of masses

a) 3sec

b) 4 sec

c) 6.53 sec

d) 7 sec

Solution:

a) We will first find where and when the two balls collide. Let us assumethat the balls collide at time t after they have been set into motion. At thisinstant t when two balls collide they are at the same height h from the groundas shown below in the figure.

The height of the first ball after t seconds = 49t-0.5(9.8t²) =4.9t(20-t)

Height of second ball after t secinds = 98 - downwards distance moved by itin t seconds

=98-0.5t²=4.9(20-t²)

therefore, 4.9t(20-t)=4.9(20-t²)

or, 10t-t²=20-t² or t=2s

b) The ball thus collides 2s after the start of their motion. Theirvelocities at this instance are

ball 1 : v₁= (49-98×2)m/s = 29.4 m/s directed upwards=29.4 i

ball 2 : v₂=(0+9.8×2)m/s = 19.6 m/s directed downwards=-19.6 i

If v is the velocity of the combined mass of two balls after theystick togather due to their collision then from law of conservation of momentum

200×v=100×29.4-100×19.6

v=4.9m/s upward direction =4.9 i

c) The joint mass thus moves upwards , after collision with a velocity of4.9 m/s. Its height above the ground at this instant is (consider the positionof either of the balls)

(98-0.5×9.8×2²)m=78.4m

We can now find the time t' taken by this joined mass of the balls to reachthe ground. For this joined mass we have

u=4.9m/s , s=78.4m , a=-g = -9.8m/s²

-78.4=4.9t'+0.5(-9.8)t²

t'²-t'-16=0

Solving the equation for t' using formula for quadratic equations and leaving out the negative solution we get t'=4.532 s

The joint mass thus takes 4.53 s to fall to the ground. Since the balls collide 2s after they started their motion ,

the total time of flight is (2+4.53) s = 6.53 s

Question on Bolr atom model

2011-11-25T04:19:00.001-08:00

Question :

The ionization energy of a hydrogen like Bohr atom is 4 rydbergs.

(a) What is the wavelength of radiation emitted when the electron jumps from the first excited state to the ground state.

(b) Whet is the radius of the first orbit of this atom ? Given that Bohr radius of hydrogen atom = 5×10^-11m and 1 rydberg = 2.2×10^-18J.

Solution :

In terms of rydberg constant R , the energy of electron in the n'th orbit of hydrogen like atom is

$E_{n} = - \frac{R Z^{2}}{n^{2}}$

where R=2.2×10^-18J. The ionization energy of the atom is

${ΔE = E}_{\infty} - E_{1} = - R Z^{2} (\frac{1}{\infty} - \frac{1}{1^{2}}) = R Z^{2}$

Given that ΔE=4R. Therefore , 4R=RZ² or, Z=2

(a) The energy of the radiation emitted when the electron jumps from the first excited state (n=2) to the ground state (n=1) is

${E = E}_{2} - E_{1} = - R Z^{2} (\frac{1}{2^{2}} - \frac{1}{1^{2}}) = \frac{3 R Z^{2}}{4} = 3 R = 3 \times 2.2 \times 10^{- 18} = 6.6 \times 10^{- 18} J$ (since Z=2)

Therefore wavelength of the radiation is given by

$λ = \frac{hc}{E} = \frac{6.63 \times 10^{- 34} \times 3 \times 10^{8}}{6.6 \times 10^{- 18}} = 301 Å$

(b) Radius of the first bohr orbit of the given atom is $= \frac{r_{1}}{Z} = 2.5 \times 10^{- 11} m$

Seeback Effect

2011-11-08T07:58:00.001-08:00

Seeback effect was first discovered by Thomas John seaback
It stated that when two different conductor are joined to form a circuit and the two junctions are held at the different temperature then an emf is developed which results in the flow of the electric current through the circuit.Arrangement is shown as below in figure
Maginitude of thermo-electric emf depends upon the nature of the two metals and on the temperature difference between terminals
Seaback effect is reversible i.e, if the hot and cold junctions are reversed the direction of thermoelectric current is alse reversed
Seaback investigated thermo-electric properties of a large number of metals and arranged them in a series known as thermo-electric series or seaback series and is given as follows
Bi,Ni,Co,Pt,Cu,Mn,Hg,Pb,Sn,Au,Ag,Zn,Cd,Fe,As,Sb,Te
When any two of these metals in the series is used to form a thermocouple ,the thermo emf is greater when two metals used are farther apart in the circuit
Figure 1 shows the thermocouple of Cu and Fe.The current in this couple flows from Cu to Fe through the hot junction
The thermo emf of this couple is only 1.3 milivolt for a temperature difference of 100 C between the hot and cold junction

Relative Velocity

2011-11-06T00:59:00.000-07:00

Question on electric charge

2011-11-05T20:43:00.000-07:00

Question
Two isolated metallic spheres of radii R and 2R are charged such that both these have the same charge densiti σ. The sphares are located far away from each other and connected by a thin conducting wire. Find the new charge density on the bigger wire.
Solution
Initial charges on sphere of radius R and 2R respectively are
Q₁= surface area × charge density = 4πR²σ
and Q₂=4π(2R)²σ = 16πR²σ
therefore Q₁+Q₂=4πR²σ+16πR²σ (1)
As the charges are different, their initial potentials are also different. When the spheres are connected by long thin conducting wire, the charges are redistributed untill their potentials become equal. Let Q'₁ and Q'₂ be the new charges on spheres of radii R and 2R respectively, their common potential is

V = \frac{1}{4 π ε_{0}} . \frac{{Q'}_{1}}{R} = \frac{1}{4 π ε_{0}} . \frac{{Q'}_{2}}{2 R}

which gives

{Q'}_{1} = \frac{{Q'}_{2}}{2}

Therefore,

{Q'}_{1} + {Q'}_{2} = \frac{3 {Q'}_{2}}{2}

From Law of conservation of charge
Q₁+Q₂=Q'₁+Q'₂
Using equation 1 and 2 we have

{Q'}_{2} = \frac{40 π R^{2} σ}{3}

The new charge density on the bigger sphere of radius R is

σ' = \frac{{Q'}_{2}}{4 π {(2 R)}^{2}} = \frac{5 σ}{6}

How to get a job

2011-10-21T11:41:00.000-07:00

Most of us who study hard to become a graduate want to find themselves a job. But there is lots of competition in the job market and you yourself would realize when you start looking for one. Apart from competition in the market you must be aware of the right option and job opening in the market. Before starting to look yourself a job you should first analyze yourself by this I mean that you must decide what you would enjoy the most at work because if you do not enjoy doing your work then you might fail to give the best you could give it.

While looking for a job engineering students might feel that lack of work experience opportunities made it much more difficult for them to get a job interview or offer in their final year even if they have all the qualifications. Most of the employers favoured students who had substantial relevant work experience. So students can go for graduate training that are offered by large number of employers. Graduate schemes enable new recruits to settle quickly into a professional work environment, receive relevant skills development and get hands on experience, either working in a specific role within an established team, or through working on a number of assignments in different areas of the organization over the duration of the program.

You can also search for graduate jobs over various websites available on internet and find the relevant jobs in your country and territory. For that you would have to design your C.V. carefully with true and relevant information about yourself. In your CV includes your abilities that are related to the jobs you are applying for. You can include skills that are relevant to the job field that you are interested in i.e. computer skills, software skills or language skills. You could find a lot of information about how to find graduate jobs on the internet and prepare according for interview and rest of the process. So I would like to say that if you manage to choose the right opportunity, you'll gain the experience which is of immense value and will ultimately make your way towards a really good job and a good pay check.

Root Mean square value of AC

2011-10-20T06:29:00.000-07:00

We know that time average value of AC over one cycle is zero and it can be proved easily

Instantaneous current I and time average of AC over half cycle could be positive for one half cycle and negative for another half cycle but quantity i² would always remain positive

So time average of quantity i² is

This is known as the mean square current

The square root of mean square current is called root mean square current or rms current.
Thus,

thus ,the rms value of AC is .707i₀ of the peak value of alternating current

Similarly rms value of alternating voltage or emf is

If we allow the AC current represented by i=i₀sin(ωt+φ) to pass through a resistor of resistance R,the power dissipated due to flow of current would be
P=i²R

Since magnitude of current changes with time ,the power dissipation in circuit also changes

The average Power dissipated over one complete current cycle would be

If we pass direct current of magnitude i_rms through the resistor ,the power dissipate or rate of production of heat in this case would be
P=(i_rms)²R

Thus rms value of AC is that value of steady current which would dissipate the same amount of power in a given resistance in a given tine as would gave been dissipated by alternating current

This is why rms value of AC is also known as virtual value of current

What is center of mass?

2011-10-20T06:19:00.000-07:00

Consider a body consisting of large number of particles whose mass is equal to the total mass of all the particles. When such a body undergoes a translational motion the displacement is produced in each and every particle of the body with respect to their original position.
If this body is executing motion under the effect of some external forces acting on it then it has been found that there is a point in the system , where if whole mass of the system is supposed to be concentrated and the nature the motion executed by the system remains unaltered when force acting on the system is directly applied to this point. Such a point of the system is called centre of mass of the system.
Hence for any system Centre of mass is the point where whole mass of the system can be supposed to be concentrated and motion of the system can be defined in terms of the centre of mass.
Consider a stationary frame of refrance where a body of mass M is situated. This body is made up of n number of particles. Let m_i be the mass and r_i be the pisition vector of i'th particle of the body.
Let C be any point in the body whose position vector with respect to origin O of the frame of refrance is R_c and position vector of point C w.r.t. i'th particle is r_ci as shown below in the figure.
From triangle OCP
r_i=R_c+r_ci (1)
multiplying both sides of equation 1 bt m_i we get
m_ir_i=m_iR_c+m_ir_ci
taking summation of above equation for n particles we get

If for a body

then point C is known as the centre of mass of the body.
Hence a point in a body w.r.t. which the sum of the product of mass of the particle and their position vector is equal to zero is equal to zero is known as centre of mass of the body.

Career opportunities in physics and engineering

2011-10-18T09:32:00.000-07:00

Majority of students studying in senior school find physics as a more difficult subject. They find difficult to gasp various theories and formulas of physics. Physics is the most fundamental of all natural sciences and it describes how nature works using the language of mathematics. Now a question arises why should a student opt to study physics when he can choose between number of other branches of science that are much easy to study and understand. I would say before opting for physics a student needs to know why the physics is important and what career options a student may get out of studying physics at senior school.

Physics is the most basic natural science. The name physics comes from the ancient Greek word for nature. And the name fits perfectly: Physics deals with everything that occurs in nature, may it be in atoms, cars, semiconductors or outer space. This all belongs to physics. Physics tries to explain natures by models. These are theoretical constructs, written in the language of logic, mathematics. Models can be falsified by experiments that show different outcome than expected, they cannot be verified.

To know the importance of physics in your daily life look around yourself and see how our daily life relies on technology, for example most of the electronic devices which are now important part of our life use transistors which came into existence due to research on physics of semiconductors and semiconductor devices and you can find lots of examples like this. Physics is an important subject to learn and understand if you are planning to make a career in medical sciences, engineering or technology. For example in case of medical sciences physics supplements a lot when it comes to be about branches like radiology.

In case of engineering studying and understanding physics becomes further more important as every branch of engineering be it electrical, mechanical or mechanical involves application of physics. The basic concepts we learn in physics play an important role in understanding complex scenarios in engineering. There are lots of career opportunities in engineering degree and if you want to opt engineering as an career option you can visit Online Engineering Degree for detailed information about different branches of engineering.

Further if you do not want to go for medical or engineering you can also opt to become a research scientist, teacher, lecturer or professor in physics. For this you would need to physics as a subject to study during graduation then go for post graduation and even have to go for a PhD degree in physics. So you see there are lots of career opportunities for a student interested in physics and there are so many reasons why you should study physics.

Uniformly accelerated motion

2011-10-18T05:40:00.000-07:00

Electric Field

2011-10-16T21:55:00.000-07:00

Student with basic knowledge of electrostatics must have studied about electric field in many books with no proper definition in most of the books. But what exactly is electric field which is only said to be existed in any region in which electric force is said to be existed and this question is not the easiest one to answer. It was Michael Faraday who first referred to an electric ‘‘field of force,’’ and James Clerk Maxwell identified that field as the space around an electrified object – a space in which electric forces act. We all know that electric field and force are closely related and most basic definition of electric field is the electric force per unit area acting on the charged object.
E=F(r)/q
where this charge q is often known as test charge.
Since electric field in general is altered by the presence of test charge

E = lim_{Δq \to 0} \frac{ΔF}{Δq} = \frac{dF}{dq}

So, it is clear from above discussion that

(1) E is a vector quantity with magnitude directly proportional to force and with direction given by the direction of the force on a positive test charge.
(2) E has units of newtons per coulomb (N/C)
While applying Gauss's law it is helpful to visualize electric field near charged object and the most common
approach is to construct a visual representation of an electric field which is to use a either arrows or ‘‘field lines’' that point in the direction of the field at each point in space as shown below

So, electric field line is an imaginary line drawn in such a way that it's direction at any point is same as the direction of field at that point.

An electric field line is, in general a curve drawn in such a way that the tangent to it ateach point is the direction of net field at that point.

Field lines of a single position charge points radially outwards while that of a negative charge are radially inwards as shown below in the figure.

Field lines around the system of two positive charges gives a different picture and describe the mutual repulsion between them.

Field lines around a system of a positive and negative charge clearly shows the mutual attraction between them as shown below in the figure.

Some important general properties of field lines are
1.Field lines start from positive charge and end on a negative charge.
2.Field lines never cross each other if they do so then at the point of intersection there will be two direction of electric field.
3.Electric field lines do not pass through a conductor , this shows that electric field inside a conductor is always zero.
4.Electric field lines are continuous curves in a charge free region.

I would like to say that you can think of electric field as a quantity filling the space in the neighborhood of an electric charge. The electric-field concept helps us understand not only the forces between isolated stationary charged bodies but also what happens when charges move. When charges move, their motion is communicated to neighboring charged bodies in the form of a field disturbance.

instantaneous velocity, speed and acceleration

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Average velocity and speed

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position, distance and displacement

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