List of top Questions asked in JEE Main- 2021

A ball is thrown up with a certain velocity so that it reaches a height 'h'. Find the ratio of the two different times of the ball reaching $\frac{h}{3}$ in both the directions.

Assertion A : If in five complete rotations of the circular scale, the distance travelled on main scale is 5 mm and there are 50 total divisions on circular scale, then least count is 0.001 cm.
Reason R : Least Count = $\frac{\text{Pitch}}{\text{Total divisions on circular scale}}$

Suppose two planets (spherical in shape) of radii R and 2 R, but mass M and 9 M respectively have a centre to centre separation 8 R as shown in the figure. A satellite of mass 'm' is projected from the surface of the planet of mass 'M' directly towards the centre of the second planet. The minimum speed 'v' required for the satellite to reach the surface of the second planet is $\sqrt{\frac{aGM}{7R}}$ then the value of 'a' is _________. [Given : The two planets are fixed in their position]

In a uniform magnetic field, the magnetic needle has a magnetic moment $9.85 \times 10^{-2}$ A/m$^2$ and moment of inertia $5 \times 10^{-6}$ kg m$^2$. If it performs 10 complete oscillations in 5 seconds then the magnitude of the magnetic field is _________ mT. [Take $\pi^2$ as 9.85]

A stone of mass 20 g is projected from a rubber catapult of length 0.1 m and area of cross section $10^{-6}$ m$^2$ stretched by an amount 0.04 m. The velocity of the projected stone is _________ m/s. (Young's modulus of rubber = $0.5 \times 10^9$ N/m$^2$)

A transistor is connected in common emitter circuit configuration, the collector supply voltage is 10 V and the voltage drop across a resistor of 1000 $\Omega$ in the collector circuit is 0.6 V. If the current gain factor ($\beta$) is 24, then the base current is _________ $\mu$A. (Round off to the Nearest Integer)

A prism of refractive index $n_1$ and another prism of refractive index $n_2$ are stuck together (as shown in the figure). $n_1$ and $n_2$ depend on $\lambda$, the wavelength of light, according to the relation $n_1 = 1.2 + \frac{10.8 \times 10^{-14}}{\lambda^2}$ and $n_2 = 1.45 + \frac{1.8 \times 10^{-14}}{\lambda^2}$. The wavelength for which rays incident at any angle on the interface BC pass through without bending at that interface will be _________ nm.

A particle of mass $9.1 \times 10^{-31}$ kg travels in a medium with a speed of $10^6$ m/s and a photon of a radiation of linear momentum $10^{-27}$ kg m/s travels in vacuum. The wavelength of photon is _________ times the wavelength of the particle.

A radioactive sample has an average life of 30 ms and is decaying. A capacitor of capacitance 200 $\mu$F is first charged and later connected with resistor 'R'. If the ratio of charge on capacitor to the activity of radioactive sample is fixed with respect to time then the value of 'R' should be _________ $\Omega$.

In Bohr's atomic model, the electron is assumed to revolve in a circular orbit of radius 0.5 Å. If the speed of the electron is $2.2 \times 10^6$ m/s, then the current associated with the electron will be _________ $\times 10^{-2}$ mA. [Take $\pi$ as 22/7]

Consider an electrical circuit containing a two way switch 'S'. Initially S is open and then $T_1$ is connected to $T_2$. As the current in R = 6 $\Omega$ attains a maximum value of steady state level, $T_1$ is disconnected from $T_2$ and immediately connected to $T_3$. Potential drop across r = 3 $\Omega$ resistor immediately after $T_1$ is connected to $T_3$ is _________ V. (Round off to the Nearest Integer)