List of top Physics Questions

Two small spheres each having equal positive charge $Q$ (Coulomb) on each are suspended by two insulating strings of equal length $L$ (metre) from a rigid hook (shown in figure). The whole set up is taken into satellite where there is no gravity. The two balls are now held by electrostatic forces in horizontal position, the tension in each string is then 

The half-life of $Ra ^{226}$ is 1620 years. Then the number of atoms decay in one second in $1 g$ of radium (Avogadro number $\left.=6.023 \times 10^{23}\right)$

The de-Broglie wavelength of an electron moving with a velocity of $1.5 \times 10^{8} m / s$ is equal to that of a photon. The ratio of kinetic energy of the electron to that of the photon $\left(c=3 \times 10^{8} m / s \right)$

Consider a disc rotating in the horizontal plane with a constant angular speed to about its centre O. The disc has a shaded region on one side of the diameter and an unshaded region on the other side as shown in the figure. When the disc is in the orientation as shown, two pebbles P and Q are simultaneously projected at an angle towards R The velocity of projection is in the y-z plane and is same for both pebbles with respect to the disc. Assume that (i) they land back on the disc before the disc has completed 1/8 rotation, (ii) their range is less than half the disc radius, and (iii) \(\omega\) remains constant throughout. Then

The unit of thermal conductivity is

A short solenoid of radius $a$, number of turns per unit length $n_{1}$ and length $L$ is kept coaxially inside a very long solenoid of radius $b$, number of turns per unit length $n_{2}$. What is the mutual inductance of the system?

Which of the two (i) compressing a gas isothermally until its volume is reduced by half (ii) compressing the same gas adiabatically until its volume is reduced by half, will require more work to be done?

A certain vector in the $x y$ plane has an $x$-component of $12\, m$ and a $y$-component of $8\, m$. It is then rotated in the $x-y$ plane so that its $x$-component is halved. Then ifs new $y$-component is approximately

Water is flowing through a very narrow tube. The velocity of water below which the flow remains a streamline flow is known as

A particle executes simple harmonic motion with amplitude A. The distance moved by the particle in one oscillation is

The current in a coil changes from 1 mA to 5 mA in 4 ms. ? If the coefficient of self-inductance of the 'coil is 10 mH,. the magnitude of "self-induced" emf is?

A block of mass 0.1 kg is held against a wall by applying a horizontal force of 5 N on it. If $\mu,$ between the wall? and the block is 0.5, the magnitude of the frictional force acting on the block is

A ring rolls down an inclined plane. The ratio of rotational kinetic energy to translational kinetic energy is

If $x =at + bt^2$ where $x$ is measured in m and t ins, thenthe dimension of (b/a) is

The ratio of speed of sound in Hydrogen to that in Oxygen at the same temperature is

The layer in earth's atmosphere which reflects radio waves from the earth thus, helping radio communication is

Two point charges $Q_1 = 2 \mu C$ and $ Q_2 = 1 \mu C$ are placed as shown. The coordinates of the point P are (2 cm, 1 cm). The electric intensity vector at P subtends an angle $\theta$ with the positive X-axis. The value of $\theta$ is given by

A particle is moving eastward with velocity $5 \, m \, s^{-1}$ In 10 s the velocity changes to $5\, m\, s^{-1}$ northwards. The average acceleration in this time is

In the case of the Bohr atom model, if $E_k$ and $U$ are the kinetic and potential energies of an electron in an orbit then,

A mass of 0.1 kg is hung at the 20 cm mark from a 1 m rod weighing 0.25 kg pivoted at its centre. The rod will not topple if

A glass hemisphere of radius 0.1 cm and refractive index 1.5 is placed over a spot on a table and the spot is viewed from above. The spot appears to be

According to Faraday's law of electromagnetic induction, an emf is induced in a coil if

The carrier of electromagnetic interaction is

"Plum pudding" model of an atom was proposed by