PHY101 Short notes
Q#1) Define charge density
When the charges are continuously over a
region-a line, the surface of a material, or inside a
sphere-we must specify the charge density.
Depending upon how many dimensions the region
has, we define:
(a) For linear charge distribution: dq ds
(b) For surface charge distribution: dq dA
(c) For volume charge distribution: dq dv
The dimensions of are determined from the above
definitions.
Q#2) Define Gauss’s Law?
Ans: The total electric flux leaving a closed
surface is equal to the charge enclosed by the surface
divided by .We can expressed in mathematics form
.
qenclosed
E d A
Q#3) Define electric potential?
Ans: The electric potential is the energy of a unit
charge in an electric field. So in our MKS units the
unit of potential is 1Joule/Coulombs=1Volt.Another
useful unit is 1Electron Volt.
Q#4) Define 1Ev?
Ans:- One electron-volt=enrgy gained by moving
one electron charges through one volt.
=1.6 10 1 1.6 10 x C x V x J 19 19
It is useful to note that
3 6 9
1 10
1 10
1 10
Kev eV
Mev eV
Gev eV
Q#5) Given a system of charges, we can always
compute the force - and hence the potential -
That arises from them. Here are some important
general statements:
a) Potentials are more positive in regions which have
more positive charge.
b) The electric potential is a scalar quantity (a scalar
field, actually).
c) The electric potential determines the force through
F=− du/dr, and hence the electric
Field because F= qE.
d) The electric potential exists only because the
electrostatic force is conservative
Q#6) Define Capacitor?
Ans:- Two conductors isolated from one another and
from their surroundings, from a capacitor. These
conductors may be of any shape and shape, and at
any distance from each other.
If a potential difference is created between the
conductors (say, by connecting the terminals of a
battery to them), then there is an electric field in the
space between them. The electric field comes 3
the charges that have been pushed to the plates by the
battery. The amount of charge pushed on to the
conductors is proportional to the potential difference
between the battery terminals (which is the same as
between the capacitor plates). HenceQ V . To convert
this into equality, we write Q CV . This provides the
definition of capacitance,C Q
V
Q#7) Define Ampere?
Ans:- Electric current is the flow of electrical charge.
If a small amount of charge dq flows in time dt, then
the current is i dq
dt
. If the current is constant in time,
then in time t, the current that flows isq i x t . The unit
of charge is ampere, which is defined as:
1
1ampere Coulombs
Second
A car’s battery supplies up to 50 amperes when
starting the car, but often we need to deal with
smaller values:
3
6
9
12
1 1 10
1 1 10
1 1 10
1 1 10
miliampere ma A
microampere A A
nanoampere nA A
picoampere pA A
Q#8) Define Resistance?
Ans:- Resistance is directly proportional to the
voltage V and inversely proportional to the current I.
V
R
I
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Imp:-
When resistors are put in series with each other, the
same current flows through both.
When current flows in a circuit work is done.
Q#9) Unit and definition of power?
Ans:- This is an important formula. It can also be
written as P V 2
R
or as p iV .The unit of power
is:1 1 1 1 .
sec sec
joule coulomb joule
volt ampere watt
coulomb ond ond
Q#10) Define Kirchhoff’s Law
Ans: - The sum of the potential differences
encountered in moving around a Closed circuit is
zero.
0
a
V iR
Q#11) Define magnetic field
Ans: - The magnetic field exerts a force upon any
charge that moves in the field. The greater the size of
the charge, and the faster it moves, the larger the
force. The direction of the force is perpendicular to
both the direction of motion and the magnetic field. If
is the angle between v and B then F qvB sin is the
magnitude of force.
The unit of magnetic field that is used most
commonly is the tesla. A charge of one Coulomb
moving at 1 meter per second perpendicularly to a
field of one tesla experiences 5
a force of 1 Newton tesla. Equivalently,
1 1 1 104 ( )
. / sec .
newton newton
tesla gauss CGS unit
coulomb meter ond ampere meter
4
10 2
1
5
Earth Surface T 10
Bar magnet T
Powerful electromagnet T
Superconducting magnet T
Q#12) Define Lorentz force
Ans:- When both magnetic and electric fields are
present at a point, the total force acting upon a charge
is the vector sum of the electric and magnetic
forces,F qE qv x B .This is called Lorentz force.
Q#13) Define Weber?
Ans: - The dimension of flux is magnetic field x area,
and the unit is called Weber.
1 1 weber tesla meter . 2
Q#14) Define alternating current
Ans: - Alternating current (AC) is current that flows
first in one direction along a wire, and then in the
reverse direction.
Q#15) Red Light has 700nm .The frequency can v
can be calculated as?
Ans:-
8
14
7
3 0 10
4 29 10
7 10
.
sec
.
m
x
v x Hertz
x m
Q#16) Define Emission?
Ans: - Matter releases energy as light.
Q#17) Define Absorption?
Ans: - Mater takes energy from light.
Q#18) Define Transmission?
Ans:- Matter allows light to pass through it.
Q#19) Define Reflection?
Ans: - Matter repels light in another direction.
Q#20) Define Diffraction?
Ans: - The bending of light around objects (into what
would otherwise be a shadowed region) is known as
diffraction. Diffraction occurs when light passes
through very small apertures or near sharp edges.
Q#21) Define statically mechanics
Ans: - The study of heat, considered as arising from
the random motion of the basic constituents of
matter, is an area of physics called statistical
mechanics.
Q#22) what are the lifetime of the polonium,
krypton, strontium, radium, carbon and
uranium?
Ans: -
Q#23) what are the basics solar facts?
214 4
84
89
36
90
38
226
88
14
6
238
92
1 64 10
3 16
28 5
1600
5760
4 5 109
.
. min
.
.
Polonium P x s
Krypton K utes
Stronium Sr years
Radium Ra years
Carbon C years
Uranium U x years
Ans: -
30
9
a) Mass of sun 2 x10 kg = 333,000 Earth's
b) Diameter of sun 1, 392, 000 km = 10 Earth's
c) Age of sun 4.6 billion years
d) Rotation Period = 25 days at equator, 36 at poles (surface)
e) Tem perature = 15 million K at core, 5770 K at surface
f) Density = 8 xgold at the core, average is ~ 1.5 water
g) Composition: 72% H, 25% He, rest is metals
Q#24) In a cool room, a metal or marble table top feels
much colder to the touch than does a wood surface even
though they are at the same temperature. Why?
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Because metal and stone conduct heat better than wood. Skin temperature is
higher than room temperature, so when we touch metal, we give heat more quickly to
the metal than wood. Another reason is that metal and stone store more energy than a
like sized object of wood
Q#25) Initial is pushing but the box does not move.
What is the force of static friction shown in below
figure?
If there is no relative motion between objects in contact, then the friction force (if there is ...
When the truck accelerates and the box moves with ... directed opposite to the way you are
walking, but the force of static friction ... shown in Figure 5.2. ... Step 2 - What is the force of
friction acting on the box if you push horizontally on.
Q#26) is it true to say that Centre of mass and Centre
of graving are the same? Either yes or no explain in
each case.
Many people assume that the terms “centre of mass” and “centre of gravity” are
synonymous, but this is not the case. ... The centre of mass and the centre of gravity of
an object are in the same position if the gravitational field in which the object exists is
uniform.
Q#27) Describe a few examples in which the force of
friction exerted on an object is in the direction of
motion of the object.
Example is an object travelling with a moving object. If you are on a train, the
relative motion of you to the train is backward because you don't move.
Q#28) Is it possible for two objects to be in thermal
equilibrium if they are not in content with each other?
Explain.
According to the law of thermodynamics, the two objects which are not in contact with
each other may be in thermal equilibrium.
Q#29) Wave spend in a string is a fiction of frequency,
so if the wave frequency, will the wave speed increase
to?
Ans If speed = frequency * wavelength. ... That means speed is directly proportional
to frequency. When frequency increases, speed increases and vice versa.
Q#30) A 2000kg car is moving with a velocity of 20 m/s
collides and locks with a 1500 kg car at rest a stop sign.
Show the momentum is conserved.
A 2000-kg car moving with a speed of 20 m/s collides with and
sticks to a 1500-kg car at rest at a stop sign. Show that because
momentum is conserved in the rest frame, momentum is also
conserved in a reference frame moving with a speed of 10 m/s in
the direction of the moving car
Q#31)
Light from sun takes approximately 8.3 min to reach
the earth during the earth is rotating with the constant
speed continuously. How far is the actual direction of
the sun?
Ans:
z = 149.4 million km.
Explanation:
This is fairly simple you just have to remember a simple equation.
z = c * t
if you know the time that light takes to reach us then you can
calculate the distance to that object and vice versa.
In the above equation,
z is the distance to the object.
t is the time light takes from the object to reach us
c is the speed of light which is always constant about 300,000 km/
sec.
The time light takes to reach us from the Sun is about 8.3 minutes.
z = 8.3 * 300,000
Note that the speed of light is in units of km/ sec so we will have to
convert minutes into seconds.
1 minute = 60 seconds
8.3 minutes = 8.3 * 60
8.3 minutes = 498 seconds.
z = 498 * 3
z = 149400000 km
OR
z = 149.4 million km.
Q#32) Do all current-carrying conductors emit
electromagnetic waves?
... Yes all current carrying conductors emit electromagnetic waves, and these are at
the right angle of the current passes through as right hand rule of Fleming's explains it.
Q#33)If you hold water in a paper cup over flame, can
you bring the water to boil, if then how?
Just fill a paper cup with water and start trying to burn it from the outside. The water
will boil vigorously inside the cup, but the paper itself wills not combust. ... The boiling
water can't get above 212 degrees, and the paper is thin enough that this water keeps its
temperature from climbing high enough to combust.
Q#34) All objects radiate energy then why are we not
able to see all the objects in the dark?
Our eyes are not sensitive to infrared radiation so we do not see it. Cold
bodies radiate mostly in the infrared zone (invisible to the human eye), but as the
temperature increases the body will emmit higher frequencies with more intensity. So
room temperature objects will not be seen due to black body radiation.
Q#35) If an electron and proton have same De
Broglie’s wavelength, which particle has greater speed
The de Broglie wavelength of a particle is inversely proportional to its
momentum p = m v; since a proton is about 1800 times more massive than
an electron, its momentum at the same speed is 1800 times that of an
electron, and therefore its wavelength 1800 times smaller. The electron has
the longer wavelength.
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Q#36) Explain why mercury rises in
thermometer when is it put in the hot water?
It consists of a bulb containing mercury which is then attached to a narrow
glass tube. As temperature rises, the level of mercury in the
tube increases. This happens because the volume
of mercury slightly increases with temperature.
Q#37) Why is glass transparent to visible light but
opaque to UV light?
Beyond the range of UV light (wavelength >400 nm), the energy
of visible and infrared light are not enough to excite the electrons and most
of the incident light gets transmitted. Thus glass appears transparent to
visible and infrared light
Q#38) If a120v line to a socked is limited to15a by a
safety fuse will it operate a 1200w hair dryer?
Q#39) wearing a metal bracelet in a region of
strong magnetic filled could be hazardous?
Answer. As the bracelet is metallic it will be pulled towards the strong
magnetic force acting around it, and you can also be pulled with
the bracelet if the force is strong enough which can cause ham to you.
Q#40) what is the changing in entropy of 1mol of
water at0c that freeze?
Showing results for explain the fusion reactions sun?
Inside the Sun, this process begins with protons (which is simply a lone
hydrogen nucleus) and through a series of steps. These protons fuse together
and are turned into helium. This fusion process occurs inside the core of
the Sun, and the transformation results in a release of energy that keeps
the sun hot.
If a total charge inside a surface is known but the distribution
of the charge is unspecified can u use the cause?
No. We can’t find the electric field if we don't know the exact charge distribution. This is
because symmetry might not be there and we can’t use Gauss theorem.
Law to find the electric field all object radiate energy?
The experimental Stefan's law states that the total power of radiation emitted across the
entire spectrum of wavelengths at a given temperature is proportional to the
fourth power of the Kelvin temperature of the radiating body.
is Heisenberg’s uncertainly principal a case of using the meter
to measure the temperature of glass of water?
For example, for a thermometer to measure the temperature of a glass of water, it is
put into thermal contact with the water. Heisenberg's uncertainty principle , however,
is not the same as the observer effect ... When you are studying the movement of
electrons, this ceases to be the case
Do you think light was wave nature and particle nature .give
strong reason?
Dual nature of light as "both a particle and a wave" has been proved. it’s essential
theory was further evolved from electromagnetic into quantum mechanics. Einstein
believed light is a particle (photon) and the flow of photons is a wave.
Do you agree or not that stationary charge or steady current
can produce electromagnetic waves?
Maxwell's four equations describe how electric charges and currents create electric ...
that there are no “magnetic charges” analogous to electric charges, and that ...
waves are the combination of electric and magnetic field. waves produced by both
electric and magnetic fields in an electromagnetic wave will fluctuate in
Do you agree or not that stationary charge or steady current
can produce electromagnetic waves?
An electromagnetic wave can be created by accelerating chargers.
Charges moving back and forth will produce oscillating electric
and magnetic fields and these travels at the speed of light.
Stationary charges and constant currents are not accelerating.
Hence it cannot produce electromagnetic waves.
What happens to current in other lamps if one lamp in
a series circuit burns out?
The same current flows through each part of a series circuit. If the circuit is broken
at any point there won't be any current that will flow. ... In this case, if one of
the bulbs blew out, the other bulb would not be able to light up because the flow of
electric current would have been interrupted.
Given that electrons behave like waves, how is droppler shift
described in terms of momentum.
Today, this idea is known as de Broglie's hypothesis of matter waves. ... a new
theory of wave quantum mechanics to describe the physics of atoms and ...
and momentum is a de Broglie wave of frequency f and wavelength λ: ... that
an electron in a hydrogen atom behaves not like a particle but like a wave.
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