List of top Questions asked in JEE Main- 2021

For extrinsic semiconductors; when doping level is increased;

Match List I with List II.

Choose the correct answer from the options given below:

The truth table for the following logic circuit is:

Two particles having masses 4 g and 16 g respectively are moving with equal kinetic energies. The ratio of the magnitudes of their linear momentum is n : 2. The value of n will be ________ .

The initial velocity $v_i$ required to project a body vertically upward from the surface of the earth to reach a height of 10R, where R is the radius of the earth, may be described in terms of escape velocity $v_e$ such that $v_i = \sqrt{\frac{x}{11}} v_e$. The value of x will be ________ .

The percentage increase in the speed of transverse waves produced in a stretched string if the tension is increased by 4 percent , will be ________ .

If $\vec{P} \times \vec{Q} = \vec{Q} \times \vec{P}$, the angle between $\vec{P}$ and $\vec{Q}$ is $\theta$ (0°<$\theta$<360°). The value of '$\theta$' will be ________°.

A reversible heat engine converts one-fourth of the heat input into work. When the temperature of the sink is reduced by 52 K, its efficiency is doubled. The temperature in Kelvin of the source will be ________ .

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]

Two identical conducting spheres with negligible volume have 2.1 nC and –0.1 nC charges, respectively. They are brought into contact and then separated by a distance of 0.5 m. The electrostatic force acting between the spheres is ________ $\times$ 10⁻⁹ N. [Given : $4\pi\epsilon_0 = \frac{1}{9 \times 10^9}$ SI unit]

The peak electric field produced by the radiation coming from the 8 W bulb at a distance of 10 m is $\frac{x}{10} \sqrt{\frac{\mu_0 c}{\pi}} \frac{V}{m}$. The efficiency of the bulb is 10% and it is a point source. The value of x is ________ .

A current of 6 A enters one corner P of an equilateral triangle PQR having 3 wires of resistance 2 $\Omega$ each and leaves by the corner R. The currents $i_1$ in ampere is ________ .