JEE Main Practice Test- 21 - JEE MCQ

What fraction of a radioactive material will get disintegrated in a period of two half-lives

The angular speed of an engine wheel making 90 revolutions per minute is

What percentage of original radioactive atoms is left after five half lives ?

An electric dipole is placed along the X-axis at the origin O. A point P is at a distance of 20 cm from this origin such that OP makes an angle π/3 with the X axis. If electric field at P makes an angle θ with X-axis, the value of θ is

Photons of energy 5.5eV fall on the surface of the metal emitting photoelectrons of maximum kinetic energy 4.0eV. The stopping potential required for these electrons are :

A man of mass 60 kg. records his wt. on a weighing machine placed inside a lift. The ratio of wts. of man recorded when lift is ascending up with a uniform speed of 2 m/s to when it is descending down with a uniform speed of 4 m/s will be

A boat of mass 40 kg is at rest. If a dog of mass 4 kg moves in the boat with a velocity of 10 m/s, then velocity of a boat will be

A microammeter has a resistance of 100 Ω and full scale range of 50 μ A. It can be used as a voltmeter or as a higher range ammeter provided a resistance is added to it. Pick the correct range and resistance combination

Spherical balls of radius R are falling in a viscous fluid of viscosity η with a velocity v. The retarding viscous force acting on the spherical ball is

The symbolic representation of four logic gates are given below:


The logic symbols for OR, NOT and NAND gates are respectively:

The size of nucleus of an atom of mass number A is proportional to

A ball is moving to and fro about the lowest point A of a smooth hemisphrical bowl. If it is able to rise up to a height of 20 cm on either side of A, its speed at A must be (Take = 10 m/s^2. mass of the body 5 g)

In the following question, a Statement of Assertion (A) is given followed by a corresponding Reason (R) just below it. Read the Statements carefully and mark the correct answer-
Assertion(A): By the study of positive rays, Thomson discovered the existence of isotopes.
Reason(R): Thomson obtained two parabolas for neon gas whose atomic mass is 20.2 .

In the following question, a Statement of Assertion (A) is given followed by a corresponding Reason (R) just below it. Read the Statements carefully and mark the correct answer-
Assertion(A): When a massive projectile collides with a lighter stationary target then maximum speed of target is twice that of projectile.
Reason(R): It is explained by the momentum and energy conservation.

Two rings of the same radius and mass are placed such that their centres are at a common point and their planes are perpendicular to each other. The moment of inertia of the system about an axis passing through the centre and perpendicular to the plane of one of the ring is (mass = and radius = r)

A process in which volume remains constant is called

Erg-m^⁻1 can be the unit of measure for

The H α line is the first member of the Balmer series of the hydrogen spectrum and it occurs due to the transition of the electron from the 3^rd orbit to the 2^ndorbit. If its wave length is λ , the wave length of the last member of the Balmer series will be

If the charge on a capacitor is increased by 2 coulomb, the energy stored in it increases by 21%. The original charge on the capacitor is

A particle is moving on a circular path with constant speed, then its acceleration will be

At what temperature will the resistance of a copper wire be three times its value at 0ºC? (Given Temperature coefficient of resistance for copper = 4x10⁻³ºC⁻¹)

How many electrons must be removed from each of two 5.0-kg copper spheres to make the electric force of repulsion between them equal in magnitude to the gravitational attraction between them?

There are three voltmeters of the same range but of resistance 10000 Ω, 8000 Ω and 4000 Ω respectively. The best voltmeter among these is the one whose resistance is