JEE Main 2020 Physics Paper: 9 Jan, Shift 2

In LC circuit the inductance L = 40 mH and

capacitance C = 100 $\mu$F. If a voltage

V(t) = 10sin(314t) is applied to the circuit, the

current in the circuit is given as:

The energy required to ionise a hydrogen like ion in its ground state is 9 Rydbergs. What is the wavelength of the radiation emitted when the electron in this ion jumps from the second excited state to the ground state?

A rod of length L has non-uniform linear mass

density given by $\rho$(x) = $a + b\left(\frac{x}{L}\right)^2$, where a

and b are constants and 0 $\leq$ x $\leq$ L. The value

of x for the centre of mass of the rod is at:

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________.

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 plane electromagnetic wave is propagating along the direction $\frac{\hat{i} + \hat{j}}{\sqrt{2}}$, with its polarization along the direction $\hat{k}$. The correct form of the magnetic field of the wave would be (here B0 is an appropriate constant):

An electric field $\vec{E} = 4x\hat{i} - (y^{2} + 1)\hat{j}$ N/C

passes through the box shown in figure. The

flux of the electric field through surfaces ABCD

and BCGF are marked as $\phi_{I}$ and $\phi_{II}$

respectively. The difference between $(\phi_{I} - \phi_{II})$ is (in Nm2/C) _______.

Planet A has mass M and radius R. Planet B has half the mass and half the radius of Planet A. If the escape velocities from the Planets A and B are vA and vB, respectively, then $\frac{v_A}{v_B} = n$ $4$. The value of n is:

Two gases-argon (atomic radius 0.07 nm, atomic weight 40) and xenon (atomic radius 0.1 nm, atomic weight 140) have the same number density and are at the same temperature. The ratio of their respective mean free times is closest to:

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:

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:

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 its axis with an angular velocity $\omega$, (k $\gg m\omega^2$) the relative change in the length of the spring is best given by the option:

A particle starts from the origin at t = 0 with an

initial velocity of 3.0 $\hat{i}$ m/s and moves in the

x-y plane with a constant acceleration $\left(6\hat{i} + 4\hat{j}\right)$ m/s2. The x-coordinate of the particle at the instant when its y-coordinate is 32 m is D meters. The value of D is :-

There is a small source of light at some depth below the surface of water (refractive index = $\frac{4}{3}$) 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 2$\pi$rh]:

A uniformly thick wheel with moment of inertia I and radius R is free to rotate about its centre of mass (see fig). 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:

The current i in the network is:

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 = CR is QA and QB respectively, then (Here e is the base of natural logarithm)

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

A small spherical droplet of density d is floating exactly half immersed in a liquid of density $\rho$ and surface tension T. The radius of the droplet is (take note that the surface tension applies an upward force on the droplet):

Starting at temperature 300 K, one mole of an

ideal diatomic gas ($\gamma$ = 1.4) is first compressed

adiabatically from volume V1 to V2 = $\frac{V_1}{16}$. It is

then 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) _____.

For the four sets of three measured physical quantities as given below. Which of the following options is correct?

(i) A1 = 24.36, B1 = 0.0724, C1 = 256.2

(ii) A2 = 24.44, B2 = 16.082, C2 = 240.2

(iii) A3 = 25.2, B3 = 19.2812, C3 = 236.183

(iv) A4 = 25, B4 = 236.191, C4 = 19.5

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:

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 $\lambda$ is used. Then the value of $\lambda$ is (in nm) __________.