COMEDK 2020

For a series L-C-R circuit at resonance, which statement is not true?

An electron of an atom transits from \(n_1\) to \(n_2\). In which of the following maximum frequency of photon will be emitted?

Two protons are kept at a separation of 40 \(\mathop A\limits^o\). F\(_n\) is the nuclear force and F\(_e\) is the electrostatic force between them. Then,

Two radioactive materials X\(_1\) and X\(_2\) have decay constant 5\(\lambda\) and \(\lambda\), respectively. If initially they have the same number of nuclei, then the ratio of the number of nuclei of X\(_1\) to X\(_2\) will be \(1/e\) aft...

Two capacitors \(C_1\) and \(C_2\) are charged to 120 V
and 200 V, respectively. When they are
connected in parallel, it is found that potential
on each one of them is zero. Therefore,

A body of mass 1000 kg is moving horizontally
with a velocity 50 m/s. A mass of 250 kg is
added. Find the final velocity.

Ground waves have wavelength

If voltage \(V=(200\pm 8)V\) and current \(I=(20\pm0.5)A\), then the percentage error in resistance R is

Point out the right statements about the validity
of Kirchhoff’s junction rule,

If \(P=Q=R=10\Omega\) and \(S=20\Omega\), then what resistance should be joined with S to balance the Wheatstone's network?

To the potentiometer wire of length L and 10\(\Omega\) resistance, a battery of emf 2.5 V and a resistance R are connected in series. If a potential difference of 1 V is balanced across L/2 length, the value of R in \(\Omega\) will be

Light of frequency 1015 Hz falls on a metal surface of work function 2.5 eV. The stopping potential of photoelectrons (in V) is

A proton accelerated through a potential V has de-Broglie wavelength \(\lambda\). Then, the de-Broglie wavelength of an \(\alpha\)-particle, when accelerated through the same potential V is

The Poisson's ratio of a material is 0.1. If the longitudinal strain of a rod of this material is \(10^{-3}\), then the percentage change in the volume of the rod will be

A steel wire of length 4.7 m and cross-sectional area \(3.0\times10^{-5}\) m\(^2\) stretches by the same amount as a copper wire of length 3.5 m and cross-sectional area of \(4.0\times10^{-5}~\mathrm{m^2}\) under a given load. What is the r...

A coil of wire of a certain radius has 100 turns
and a self inductance of 15 mH. The self
inductance of a second similar coil of 500 turns
will be

A coil of 100 turns carries a current of 5 mA and
creates a magnetic flux of 10\(^{-5}\) Wb. The
inductance is

In step-up transformer, relation between number of turns in primary (N\(_P\)) and number of turns in secondary (N\(_S\)) coils is

Which of the following has/have zero average
value in a plane electromagnetic wave?

Consider a thin spherical shell of radius R
consisting of uniform surface charge density s.
The electric field at a point of distance x from its
centre and outside the shell is

A charge of 0.8 C is divided into two charges Q\(_1\) and Q\(_2\). These are kept at a separation of 30 cm. The force on Q\(_1\) is maximum when

An electric dipole has a pair of equal and opposite point charges \(q\) and \(-q\) separated by a distance \(2x\). The axis of the dipole is defined as

An electric dipole is placed in a uniform electric
field with the dipole axis making an angle \(\theta\) with
the direction of the electric field. The
orientation of the dipole for stable equilibrium
is

Two point charges A = +3 nC and B = +1 nC are placed 5 cm apart in air. The work done to move charge B towards A by 1 cm is

The potential energies associated with four
orientations of an electric dipole in an electric
field are
(i) \(-5U_0\) (ii) \(-7U_0\) (iii) \(3U_0\) (iv) \(5U_0\)
where \(U_0\) is positive. Rank the orientations according to the angle betwee...

A ball floats on the surface of water in a
container exposed to the atmosphere. When the
container is covered and the air is partially
removed, then the ball

A frame made of metallic wire enclosing a surface area A is covered with a soap film. If the area of the frame of metallic wire is reduced by 50%, then the energy of the soap film will be changed by

A fluid is in streamline flow across a horizontal
pipe of variable area of cross-section. For this
which of the following statements is correct?

A satellite can be in a geostationary orbit around a planet if it is at a distance R from the centre of the planet. If the planet starts rotating about its axis with double the angular velocity, then to make the satellite geostationary, its...

Two spherical bodies of masses M and 5M and
radii R and 2R are released in free space with
initial separation between their centres equal to
12 R. If they attract each other due to
gravitational force only, then the distance
covered by the ...

A compound slab is made of two parallel plates
of copper and brass of the same thickness and
having thermal conductivities in the ratio 4 : 1.
The free face of copper is at 0\(^\circ\)C. The
temperature of the interface is 20\(^\circ\)C. Wh...

In mm\(^3\) of a gas is compressed at 1 atmospheric pressure and temperature 27\(^\circ\)C to 627\(^\circ\)C. What is the final pressure under adiabatic condition?
(\(\gamma\) for the gas = 1.5)

If sink is at a temperature of \(-39\Upsilon\)C and source at 0\(^\circ\)C, then efficiency will be

Equal volumes of two gases, having their
densities in the ratio of 1 : 16 exert equal
pressures on the walls of two containers. The
ratio of their rms velocities \(\left(\frac{c_1}{c_2}\right)\)

A gaseous mixture consists of 16 g of helium and 16 g of oxygen. The ratio \(C_p/C_V\) of the mixture is

Which of the following laws of Physics is valid
across all domains of nature?

A body under the action of a force \(F = 6\widehat i - 8\widehat j + 10\widehat k\), acquires an acceleration of 1 m/s2. The mass of this body must be

The intensity of magnetic field due to an isolated pole of strength \(m_p\) at a point distant \(r\) from it will be

The angle which the total magnetic field of
earth makes with the surface of the earth is
called

The angle of dip of at a place where horizontal
and vertical components of earth’s magnetic
field are equal is

A body is projected vertically upwards. The
times corresponding to height \(h\), while
ascending and while descending are \(t_1\) and \(t _2\) ,
respectively. Then, the velocity of projection is
(\(g\) is acceleration due to gravity)

A particle shows distance-time curve as given in
this figure. The maximum instantaneous
velocity of the particle is around the point

An electron moves with speed of 2 \(\times\) 10\(^5\) m/s along the positive x-direction in a magnetic field \(B = (\widehat i - 4\widehat j - 3\widehat k)\,T\). The magnitude of the force (in N) experienced by the electron is

A horizontal overhead power line carries a
current of 90 A in East to West direction. What
is the magnitude and direction of the magnetic
field due to the current, 1.5 m below the line?

A moving coil galvanometer has 28 turns and area of coil is \(4\times 10^{-2}\) m\(^2\). If the magnetic field is 0.2 T, then to increase the sensitivity by 25% without changing area and field, the number of turns should be changed to

The particle that cannot be accelerated by a cyclotron is

A convex lens is made of 3 layers of glass of 3 different materials as in the figure.

A point object is placed on its axis. The number
of images of the object are

A ray of light suffers minimum deviation in
equilateral prism P. Additional prisms Q and R
of identical shape and of same material as that of
P are now combined as shown in figure. The ray
will now suffer

Four particles each of the mass m are placed at
the corners of a square of side length \(l\). The
radius of gyration of the system about an axis
perpendicular to the square and passing
through its centre is

The masses of 200 g and 300 g are attached to
the 20 cm and 70 cm marks of a light meter rod,
respectively. The moment of inertia of the
system about an axis passing through 50 cm
mark is