Mechanical waves require the presence of a medium.
Electromagnetic waves can propagate through empty space.
Maxwells equations form the theoretical basis of all electromagnetic waves that
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MCQs of Plasma Physics
by Prof. V.K. Tripathi , IIT Delhi, New Delhi.
Problem 1: Consider a singly ionized sphere of electron density no, radius R and electron
temperature T. Due to thermal motions electrons of the layer of width near the surfac
Units And Measurements (Physics)
Fill in the blanks
The volume of a cube of side 1 cm is equal to.m3
The surface area of a solid cylinder of radius 2.0 cm and height 10.0 cm is equal to .
A vehicle moving with a speed of 18 km h1covers
In which of the following examples of motion, can the body be considered approximately
a point object:
a railway carriage moving without jerks between two stations.
a monkey sitting on top of a man cycling smoothly on a circular track.
State, for each of the following physical quantities, if it is a scalar or a vector:
volume, mass, speed, acceleration, density, number of moles, velocity, angular frequency,
displacement, angular velocity.
Scalar: Volume, mass, speed
Give the magnitude and direction of the net force acting on
a drop of rain falling down with a constant speed,
a cork of mass 10 g floating on water,
a kite skilfully held stationary in the sky,
a car moving with a constant velocity of 30 km
The sign of work done by a force on a body is important to understand. State carefully if
the following quantities are positive or negative:
work done by a man in lifting a bucket out of a well by means of a rope tied to the bucket.
Give the location of the centre of mass of a (i) sphere, (ii) cylinder, (iii) ring, and (iv)
cube, each of uniform mass density. Does the centre of mass of a body necessarily lie
inside the body?
Geometric centre; No
The centre of mas
Answer the following:
You can shield a charge from electrical forces by putting it inside a hollow conductor.
Can you shield a body from the gravitational influence of nearby matter by putting it
inside a hollow sphere or by some other means
A steel wire of length 4.7 m and cross-sectional area 3.0 105 m2 stretches by the same
amount as a copper wire of length 3.5 m and cross-sectional area of 4.0 105 m2 under a
given load. What is the ratio of the Youngs modulus of steel to tha
The blood pressure in humans is greater at the feet than at the brain
Atmospheric pressure at a height of about 6 km decreases to nearly half of its value at the
sea level, though the height of the atmosphere is more than 100 km
The triple points of neon and carbon dioxide are 24.57 K and 216.55 K respectively.
Express these temperatures on the Celsius and Fahrenheit scales.
Kelvin and Celsius scales are related as:
TC = TK 273.15 (i)
Celsius and Fahrenheit
A geyser heats water flowing at the rate of 3.0 litres per minute from 27 C to 77 C. If
the geyser operates on a gas burner, what is the rate of consumption of the fuel if its heat
of combustion is 4.0 104 J/g?
Water is flowing at a
Estimate the fraction of molecular volume to the actual volume occupied by oxygen gas
at STP. Take the diameter of an oxygen molecule to be 3.
Diameter of an oxygen molecule, d = 3
= 1.5 = 1.5 108 cm
Actual volume occupied
Which of the following examples represent periodic motion?
A swimmer completing one (return) trip from one bank of a river to the other and back.
A freely suspended bar magnet displaced from its N-S direction and released.
A hydrogen mol
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Balls in a semicircle
(a) Let M/N be the mass of each ball in the semicircle. We need the deection
angle in each collision to be = /N . However, if the ratio /m is too small,
then this angle of deection is not possible.
Rectangle in a circle
In the gure below, let the incenters of triangles ADB and ADC be X and Y ,
Angle XAY can be written as
XAD Y AD
A similar argument
(a) We will take advantage of the fact that a cone is at, in the sense that we
can make one out of a piece of paper, without crumpling the paper.
Cut the cone along a straight line emanating from the peak and pa
The strategy here will be to compute the moment of inertia by using scaling
arguments, along with the parallel-axis theorem. To do this, we will need to compare
the I for our triangle of side to that of a triangle
Product of lengths
(This clever solution and generalization comes from Mike Robinson.)
Put the circle in the complex plane, with its center at the origin. Let the given
vertex of the N -gon be located at the point (1, 0). Let a
Break or not break?
There are two possible reasonings, which seem to create a paradox:
To an observer in the original rest frame, the spaceships stay the same distance,
d, apart. Therefore, in the frame of the spaceships, the
First Solution: Let E(x) be the expected number of numbers you have yet to pick,
given that you have just picked the number x. Then, for example, E(0) = 1, because
the next number you pick is guaranteed to be
Find the angles
Although this problem seems simple at rst glance, angle chasing wont provide the
answer. Something a bit more sneaky is required. At the risk of going overboard,
well give four solutions. You can check that all
Letters in envelopes
First Solution: (This solution is due to Aravi Samuel.) We will use induction on
N . Let BN denote the number of bad congurations where none of the N letters
end up in the correct envelope. We claim that BN
Distribution of primes
A necessary and sucient condition for N to be prime is that N have no prime
factors less than or equal to N . Therefore, under the assumption that a prime p
divides N with probability 1/p, the probability
Week 21 (2/3/03)
Ball on turntable
Let the angular velocity of the turntable be , and let the angular velocity of
the ball be . If the ball is at position r (with respect to the lab frame), then its
velocity (with respect to the lab frame) may
(a) Let your envelope contain N dollars. Then the other envelope contains either
2N or N/2 dollars. If you switch, the expected value of your assets is 1 (2N ) +
(N/2) = 5N/4. This is greater than N . There
V (x) versus a hill
Quick solution: Consider the normal force, N , acting on the bead at a given
point. Let be the angle that the tangent to V (x) makes with the horizontal, as
The horizontal F = ma equation is