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

The frequency of echo will be ______ Hz if the train blowing a whistle of frequency 320 Hz is moving with a velocity of 36 km/h towards a hill from which an echo is heard by the train driver. The velocity of sound in air is 330 m/s.

A whistle producing sound waves of frequencies 9500 Hz and above is approaching a stationary person with speed v ms^-1. The velocity of sound in air is 300 ms^-1. If the person can hear frequencies up to a maximum of 10,000 HZ, the maximum value of v up to which he can hear the whistle is ______.

Two coherent sources of different intensities send waves which interfere. The ratio of maximum intensity to the minimum intensity is 25. The intensities of the sources are in the ratio ______.

A capacitor is discharging through a resistor R. Consider in time t₁, the energy stored in the capacitor reduces to half of its initial value and in time t₂, the charge stored reduces to one-eighth of its initial value. The ratio t₁/t₂ will be ______.

A parallel plate capacitor filled with a medium of dielectric constant 10, is connected across a battery and is charged. The dielectric slab is replaced by another slab of dielectric constant 15. Then the energy of capacitor will ______.

If the electric potential at any point (x, y, z)m in space is given by V = 3x² volt. The electric field at the point (1, 0, 3)m will be ______.

Two identical strings X and Z made of same material have tension T_x and T_z in them If their fundamental frequencies are 450 Hz and 300 Hz, respectively, then the ratio `"T"_x/"T"_"z"` is ______.

Shown in the figure is rigid and uniform one meter long rod AB held in horizontal position by two strings tied to its ends and attached to the ceiling. The rod is of mass 'm' and has another weight of mass 2m hung at a distance of 75 cm from A. The tension in the string at A is :

Two travelling waves produce a standing wave represented by the equation. y = 1.0 mm cos (1.57 cm^-1) x sin (78.5 s^-1)t. The node closest to the origin in the region x > 0 will be at x = ______ cm.

A wire of length 2L is made by joining two wires A and B of the same length but different radii r and 2r, and made of the same material. It is vibrating at a frequency such that the joint of the two wires forms a node. If the number of antinodes in wire A is p and that in B is q then the ratio p : q is ______.

Two closed end pipes when sounded together produce 5 beat per second. If their length are in the ratio 100 : 101, then fundamental notes produced by them are ______.

A non-conducting sphere of radius R = 5 cm has its centre at the origin O of the coordinate system. It has a spherical cavity of radius r = 1 cm having its centre at (0, 3 cm). The solid material of the sphere has a uniform positive charge density `rho = 10^-6/pi` coulomb m^-3. The potential at point P is ______ volt. (4 cm, 0).

Two uniformly charged spherical conductors A and B of radii 5 mm and 10 mm are separated by a distance of 2 cm. If the spheres are connected by a conducting wire, then in equilibrium condition, the ratio of the magnitudes of the electric fields at the surface of the sphere A and B will be:

A battery is used to charge a parallel plate capacitor till the potential difference between the plates becomes equal to the electromotive force of the battery. The ratio of the energy stored in the capacitor and the work done by the battery will be ______.

In the widest part of the horizontal pipe, oil is flowing at a rate of 2 m/sec. The speed (in m/s) of the flow of oil in the narrow part of the tube if the pressure difference in the broad and narrow parts of the pipe is 0.25 ρ_oilg, is ______ m/s.

n identical waves each of intensity I₀ interfere with each other. The ratio of maximum intensities if the interference is (i) coherent and (ii) incoherent is ______.

Calculate the velocity with which the liquid gushes out of the 4 cm² outlet, if the liquid flowing in the tube is water and the liquid in the U tube has a specificity 12. The velocity of the liquid at point A is `sqrt20.2` m/s ______.

A tuning fork is vibrating at 250 Hz. The length of the shortest closed organ pipe that will resonate with the tuning fork will be ______ cm.

(Take the speed of sound in air as 340 ms^-1.)

A tuning fork of frequency 480 Hz is used in an experiment for measuring the speed of sound (ν) in the air by resonance tube method. Resonance is observed to occur at two successive lengths of the air column, l₁ = 30 cm and l₂ = 70 cm. Then, ν is equal to ______.

A string 2.0 m long and fixed at its ends is driven by a 240 Hz vibrator. The string vibrates in its third harmonic mode. The speed of the wave and its fundamental frequency is ______.