PHYSICS 7th JAN S2 2020 - JEE MCQ
24 Questions MCQ Test - PHYSICS 7th JAN S2 2020
In a building there are 15 bulbs of 45 W, 15 bulbs of 100 W, 15 small fans of 10 W and 2 heaters of
1 kW. The voltage of electric main is 220 V. The minimum fuse capacity (rated value) of building will be:
1 kW. The voltage of electric main is 220 V. The minimum fuse capacity (rated value) of building will be:
An elevator in a building can carry a maximum of 10 persons, with the average mass of each person
being 68 kg. The mass of the elevator itself is 920 kg and it moves with a constant speed of 3 m/s. The
frictional force opposing the motion is 6000 N. If the elevator is moving up with its full capacity, the
power delivered by the motor to the elevator (g = 10 m/s2) must be at least :
being 68 kg. The mass of the elevator itself is 920 kg and it moves with a constant speed of 3 m/s. The
frictional force opposing the motion is 6000 N. If the elevator is moving up with its full capacity, the
power delivered by the motor to the elevator (g = 10 m/s2) must be at least :
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In a Young's double slit experiment, the separation between the slits is 0.15 mm. In the experiment, a
source of light of wavelength 589 nm is used and the interference pattern is observed on a screen kept
1.5 m away. The separation between the successive bright fringes on the screen is :
source of light of wavelength 589 nm is used and the interference pattern is observed on a screen kept
1.5 m away. The separation between the successive bright fringes on the screen is :
An ideal fluid flows (laminar flow) through a pipe of non-uniform diameter. The maximum and minimum
diameters of the pipes are 6.4 cm and 4.8 cm, respectively. The ratio of the minimum and the maximum
velocities of fluid in this pipe is
Two ideal Carnot engines operate in cascade (all heat given up by one engine is used by the other
engine to produce work) between temperatures, T1 and T2. The temperature of the hot reservoir of the
first engine is T1 and the temperature of the cold reservoir of the second engine is T2. T is temperature
of the sink of first engine which is also the source for the second engine. How is T related to T1 and T2,
if both the engines perform equal amount of work
A planar loop of wire rotates in a uniform magnetic field. Initially at t = 0, the plane of the loop is
perpendicular to the magnetic field. If it rotates with a period of 10 s about an axis in its plane then the
magnitude of induced emf will be maximum and minimum, respectively at
A stationary observer receives sound from two identical tuning forks, one of which approaches and the
other one recedes with the same speed (much less than the speed of sound). The observer hears
2 beats/sec. The oscillation frequency of each tuning fork is v º = 1400 Hz and the velocity of sound in
air is 350 m/s. The speed of each tuning fork is close to
A thin lens made of glass (refractive index = 1.5) of focal length f = 16 cm is immersed in a liquid of
refractive index 1.42. If its focal length in liquid is fº, then the ratio fº/f is closest to the integer
The figure gives experimentally measured B vs. H variation in a ferromagnetic material. The retentivity ,
co-ercivity and saturation, respectively, of the material are 
The activity of a radioactive sample falls from 700 s^-1 to 500 s^-1 in 30 minutes. Its half life is close to
A box weighs 196 N on a spring balance at the north pole. Its weight recorded on the same balance if it
is shifted to the equator is close to (Take g = 10 ms–2 at the north pole and the radius of the
earth = 6400 km)
The dimensions B^2/μ��, where B is magnetic field and μο is the magnetic permeability of vacuum, is
An emf of 20 V is applied at time t = 0 to a circuit containing in series 10 mH inductor and 5Ωresistor.
The ratio of the currents at time t =∞ and at t = 40 s is close to : (Take e^2 = 7.389)
An electron (of mass m) and a photon have the same energy E in the range of a few eV. The ratio of
the de-Broglie wavelength associated with the electron and the wavelength of the photon is (c = speed
of light in vacuum
A mass of 10 kg is suspended by a rope of length 4 m, from the ceiling. A force F is applied horizontally
at the mid-point of the rope such that the top half of the rope makes an angle of 45° with the vertical.
Then F equals : (Take g = 10 ms–2 and the rope to be massless
Mass per unit area of a circular disc of radius a depends on the distance r from its centre as
σ(r) = A + Br. The moment of inertia of the disc about the axis, perpendicular to the plane and passing
through its centre is
M grams of steam at 100°C is mixed with 200g of ice at its melting point in a thermally insulated
container. If it produces liquid water at 40°C [heat of vaporization of water is 540 cal/g and heat of
fusion of ice is 80 cal/g], the value of M is______.
A 60 pF capacitor is fully charged by a 20V supply. It is then disconnected from the supply and is
connected to another uncharged 60 pF capacitor in parallel. The electrostatic energy that is lost in this
process by the time the charge is redistributed between them is (in nJ)________
The balancing length for a cell is 560 cm in a potentiometer experiment. When an external resistance of
10Ω is connected in parallel to the cell, the balancing length changes by 60 cm. If the internal
resistance of the cell is N/10Ω, where N is an integer then value of N is ______.
Consider uniform cubical box of side a on a rough floor that is to be moved by applying minimum
possible force F at a point b above its centre of mass (see figure). If the coefficient of friction is µ = 0.4,
the maximum possible value of 100×b/a for box not to topple before moving is
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