JEE Main entrance exam Question Bank Solutions for Physics (JEE Main)

In U²³⁸ ore containing Uranium the ratio of U²³⁴ to Pb²⁰⁶ nuclei is 3. Assuming that all the lead present in the ore is final stable product of U²³⁸. Half life of U²³⁸ to be 4.5 × 10⁹ years and the age of ore is ______ × 10⁹ years. (in 10⁹ years)

A displacement vector, at an angle of 30° with y-axis has an x-component of 10 units. Then the magnitude of the vector is ______.

The formula `S = ut - 1/3 at^2` where S is the distance travelled, u is the initial velocity, a is the acceleration and t is the time is ______.

A stone is dropped from the top of the tower and travels 24.5 m in the last second of its journey. The height of the tower is ______.

(g = 9.8 m/s²)

In finding the electric field using Gauss law the formula `|vec"E"| = "q"_"enc"/(epsilon_0|"A"|)` is applicable. In the formula ε₀ is permittivity of free space, A is the area of Gaussian surface and q_enc is charge enclosed by the Gaussian surface. This equation can be used in which of the following situation?

The activity of a certain radionuclide decreases to 15 percent of its original value in 10 days. What is its half life?

[ln (0.15) = -1.9]

An engine is approaching a cliff at a constant speed. When it is at a distance of 0.9 km from cliff it sounds a whistle. The echo of the sound is heard by the driver after 5 seconds. Velocity of sound in air is equal to 330 ms^-1. The speed of the engine is ______ km/h.

A bar magnet is demagnetized by inserting it inside a solenoid of length 0.2 m, 100 turns, and carrying a current of 5.2 A. The coercivity of the bar magnet is ______.

The mean lives of a radioactive substance are 1620 and 405 years for β-emission and β-emission respectively. The time after which three fourth of a sample will decay if it is decaying both by β-emission and β-emission simultaneously will be ______ years.

(Take ln 2 = 0.693)

The displacement s of a particle depends on time t according to the following relation `s = 1/3t^3 - t^2 + t`. The velocity and displacement of the particle at the instant when its acceleration is zero, are respectively ______.

In the given figure, the face AC of the equilateral prism is immersed in a liquid of refractive index 'n'. For incident angle 60° at the side AC, the refracted light just grazes along face AC. The refractive index of the liquid n = `sqrtx/4`. The value of x is ______.

(Given refractive index of glass = 1.5)

Two perfectly identical wires kept under tension are in unison. When the tension in the wire is increased by 1% then on sounding them together 3 beats are heard in 2 seconds. What is the frequency of each wire?

White light is an incident at 20° on a material of silicate flint glass slab as shown. `μ_"violet"` = 1.66 and µ_r = 1.6. For what value of d will the separation be 1 mm in red and violet rays?

If 10% of a radioactive substance decays in every 5 years, then the percentage of the substance that will have decayed in 20 years will be ______.

A light ray in a medium (RI = 5/3) enters another medium at an angle of 30°. The angle in the other medium is sin^-1 (5/6). The incident angle must be increased such that the ray is completely reflected at minimum degrees is ______.

Two radioactive materials A and B have decay constants 25λ and 16λ respectively. If initially they have the same number of nuclei, then the ratio of the number of nuclei of B to that of A will be "e" after a time `1/("a"lambda)` The value of a ______.

A radioctive sample decays `7/8` times its original quantity in 15 minutes. The half-life of the sample is ______.

Calculate the time interval between 33% decay and 67% decay if half-life of a substance is 20 minutes.

If L, C and R are the self inductance, capacitance and resistance respectively, which of the following does not have the dimension of time?

Which of the following is not a dimensionless quantity?