List of top Questions asked in JEE Main- 2021

Statement I : By doping silicon semiconductor with pentavalent material, the electrons density increases.
Statement II : The n-type semiconductor has net negative charge.
In the light of the above statements, choose the most appropriate answer from the options given below :

An AC source rated 220 V, 50 Hz is connected to a resistor. The time taken by the current to change from its maximum to the rms value is :

If you are provided a set of resistances 2 $ \Omega $, 4 $ \Omega $, 6 $ \Omega $ and 8 $ \Omega $. Connect these resistances so as to obtain an equivalent resistance of $ \frac{46}{3} \Omega $.

Three capacitors C$_1$ = 2 $\mu$F, C$_2$ = 6 $\mu$F and C$_3$ = 12 $\mu$F are connected as shown in figure. Find the ratio of the charges on capacitors C$_1$, C$_2$ and C$_3$ respectively:

In Young's double slit experiment, if the source of light changes from orange to blue then:

A refrigerator consumes an average 35 W power to operate between temperature -10$^{\circ}$C to 25$^{\circ}$C. If there is no loss of energy then how much average heat per second does it transfer ?

The speed of electrons in a scanning electron microscope is $1 \times 10^7$ ms⁻¹. If the protons having the same speed are used instead of electrons, then the resolving power of scanning proton microscope will be changed by a factor of:

What will be the average value of energy along one degree of freedom for an ideal gas in thermal equilibrium at a temperature T ? (kB is Boltzmann constant)

Figure shows a rod AB, which is bent in a 120$^{\circ}$ circular arc of radius R. A charge ($-Q$) is uniformly distributed over rod AB. What is the electric field $\vec{E}$ at the centre of curvature O?

Curved surfaces of a plano-convex lens of refractive index $\mu_1$ and a plano-concave lens of refractive index $\mu_2$ have equal radius of curvature as shown in figure. Find the ratio of radius of curvature to the focal length of the combined lenses.

A diatomic gas, having $C_p = \frac{7}{2}R$ and $C_v = \frac{5}{2}R$, is heated at constant pressure. The ratio $dU : dQ : dW$:

Which of the following is not a dimensionless quantity ?

A light cylindrical vessel is kept on a horizontal surface. Area of base is A. A hole of cross-sectional area 'a' is made just at its bottom side. The minimum coefficient of friction necessary to prevent sliding the vessel due to the impact force of the emerging liquid is (a << A) :

A player kicks a football with an initial speed of 25 ms$^{-1}$ at an angle of 45$^{\circ}$ from the ground. What are the maximum height and the time taken by the football to reach at the highest point during motion? (Take g = 10 ms$^{-2}$)

A bob of mass 'm' suspended by a thread of length $l$ undergoes simple harmonic oscillations with time period T. If the bob is immersed in a liquid that has density $\frac{1}{4}$ times that of the bob and the length of the thread is increased by $1/3^{rd}$ of the original length, then the time period of the simple harmonic oscillations will be :

An ideal gas in a cylinder is separated by a piston in such a way that the entropy of one part is $S_1$ and that of the other part is $S_2$. Given that $S_1>S_2$. If the piston is removed then the total entropy of the system will be:

A charge 'q' is placed at one corner of a cube as shown in figure. The flux of electrostatic field $\vec{E}$ through the shaded area is:

Two particles A and B having charges $20\,\mu C$ and $-5\,\mu C$ respectively are held fixed with a separation of $5\,\text{cm}$. At what position a third charged particle should be placed so that it does not experience a net electric force ?

A soft ferromagnetic material is placed in an external magnetic field. The magnetic domains :

In the reported figure, there is a cyclic process ABCDA on a sample of 1 mol of a diatomic gas. The temperature of the gas during the process A $\rightarrow$ B and C $\rightarrow$ D are $T_1$ and $T_2$ ($T_1>T_2$) respectively. Choose the correct option out of the following for work done if processes BC and DA are adiabatic.

Figure shows a circuit that contains four identical resistors with resistance R=2.0 Ω, two identical inductors with inductance L=2.0 mH and an ideal battery with emf E=9 V. The current 'i' just after the switch 'S' is closed will be :

For extrinsic semiconductors; when doping level is increased;

A proton, a deuteron and an $\alpha$ particle are moving with same momentum in a uniform magnetic field. The ratio of magnetic forces acting on them is __________ and their speed is __________, in the ratio.

if 0<x, y<$\pi$ and cosx+cosy-cos(x y)=$\frac{3}{2}$,Then sin x+cos y=?

Two small spheres each of mass 10 mg are suspended from a point by threads 0.5 m long. They are equally charged and repel each other to a distance of 0.20 m. The charge on each of the sphere is $\frac{a}{21} \times 10^{-8} C$.
The value of 'a' will be ______. [Given g = 10 ms–2]