PHYSICS 9th JAN S2 2020 - JEE MCQ

Two steel wires having same length are suspended from a ceiling under the same load. If the ratio of
their energy stored per unit volume is 1 : 4, the ratio of their diameters is

In LC circuit the inductance L = 40 mH and capacitance C = 100 μF. If a voltage V(t) = 10sin(314t) is
applied to the circuit, the current in the circuit is given as

There is a small source of light at some depth below the surface of water (refractive index = 4/3) in a
tank of large cross sectional surface area. Neglecting any reflection from the bottom and absorption by
water, percentage of light that emerges out of surface is (nearly) :
[Use the fact that surface area of a spherical cap of height h and radius of curvature r is 2πrh]

A uniformly thick wheel with moment of inertial I and radius R is free to rotate about its centre of mass
(see figure). A massless string is wrapped over its rim and two blocks of masses m₁ and m₂ (m₁ > m₂)
are attached to the ends of the string. The system is released from rest. The angular speed of the
wheel when m₁ descents by a distance h is :

A rod of length L has non-uniform linear mass density given by ρ(x)= a+b(x/L)² where a and b are
constants and 0≤x≤L The value of x for the centre of mass of the rod is at

A particle starts from the origin at t = 0 with an initial velocity of 3.0iˆ m/s and moves in the x-y plane
with a constant acceleration=6î+4j^{^} ms².s2. The x-coordinate of the particle at the instant when its ycoordinate
is 32m is D meters. The value of D is

A particle of mass m is projected with a speed u from the ground at an angle θ = π/3 w.r.t. horizontal (xaxis).
When it has reached its maximum height, it collides completely inelastically with another particle
of the same mass and velocity uî . The horizontal distance covered by the combined mass before
reaching the ground is

An electron gun is placed inside a long solenoid of radius R on its axis. The solenoid has n turns/length
and carries a current I. The electron gun shoots an electron along the radius of the solenoid with speed
v. If the electron does not hit the surface of the solenoid, maximum possible value of v is (all symbols
have their standard meaning

A spring mass system (mass m, spring constant k and natural length ℓ) rests in equilibrium on a
horizontal disc. The free end of the spring is fixed at the centre of the disc. If the disc together with
spring mass system, rotates about it's axis with an angular velocity ω, (k>> mω²) the relative change in
the length of the spring is best given by the option

An electron of mass m and magnitude of charge |e| initially at rest gets accelerated by a constant
electric field E. The rate of change of de-Broglie wavelength of this electron at time t ignoring relativistic
effects is :

A small spherical droplet of density d is floating exactly half immerse in a liquid of density ρ and surface
tension T. The radius of the droplet is (take note that the surface tension applies an upward force on the
droplet

The current i(in A) in the network is

A small circular loop of conducting wire has radius a and carries current I. It is placed in a uniform
magnetic field B perpendicular to its plane such that when rotated slightly about its diameter and
released, it starts performing simple harmonic motion of time period T. If the mass of the loop is m then
:

Two identical capacitors A and B, charged to the same potential 5V are connected in two different
circuits as shown below at time t = 0. If the charge on capacitors A and B at time t = C_R is Q_A and Q_B
respectively, then (Here e is the base of natural logarithm)

A wire of length L and mass per unit length 6.0 × 10^-3 kgm–1 is put under tension of 540 N. Two
consecutive frequencies that it resonates at are 420 Hz and 490 Hz. Then L in meters is

Starting at temperature 300 K, one mole of an ideal diatomic gas (γ = 1.4) is first compressed
adiabatically from volume V₁to V₂ = V₁/16. it is then a allowed to expand isobarically to volume 2V₂. If
all the processes are the quasi-static then the final temperature of the gas (in ºK) is (to the nearest
integer

In a Young's double slit experiment 15 fringes are observed on a small portion of the screen when light
of wavelength 500 nm is used. Ten fringes are observed on the same section of the screen when
another light source of wavelength λ is used Then the value of λ is (in nm)

In a meter bridge experiment S is a standard resistance. R is a resistance wire. It is found that
balancing length is ℓ = 25 cm. If R is replaced by a wire of half length and half diameter that of R of
same material, then the balancing distance ℓ' (in cm) will now be 

The circuit shown below is working as a 8V dc regulated voltage source. When 12V is used as input,
the power dissipated (in mW) in each diode is ; (considering both zener diodes are
identical