List of top Physics Questions

An electron is moving in an orbit of hydrogen atom in which there can be a maximum of six transitions. Another electron is moving in another orbit of hydrogen atom in which there can be a maximum of three transitions. The ratio of the velocity of electrons in these two orbits is:

Two identical short bar magnets, each having a magnetic moment of 10 \( \text{Am}^{2} \) are arranged such that their axial lines are perpendicular to each other and their centres be along the same straight line in a horizontal plane. If the distance between their centres is 0.2 m, the resultant magnetic induction at a point midway between them is: (\( \mu_{\circ}=4\pi\times10^{-7}~\text{Hm}^{-1} \))

A circular coil of radius 8 cm, 400 turns and resistance \( 2\,\Omega \) is placed with its plane perpendicular to the horizontal component of the earth's magnetic field. It is rotated about its vertical diameter through \( 180^{\circ} \) in 0.30 sec. Horizontal component of the earth's magnetic field at the place is \( 3\times10^{-5} \) T. The magnitude of current induced in the coil is approximately:

A solar cell has a light gathering area of \( 10\,\text{cm}^{2} \) and produces 0.2 A at 0.8 V (D.C.) when illuminated with sunlight of intensity \( 1000\,\text{Wm}^{-2} \). The efficiency of the solar cell is:

An ac source has a peak voltage \( \frac{200}{\sqrt{2}} \) V and frequency 50 Hz. The value of voltage after \( \frac{1}{600} \) s from the start is:

A circular coil connected to a battery of emf E produced a magnetic field at its centre. The coil is unwound, stretched to double its length and rewound into a coil of \( \left(\frac{1}{3}\right)^{\text{rd}} \) of its initial radius. If this coil is connected to a battery of emf E' to produce same magnetic field at its centre, then E' is:

A particle of charge 'q' and mass 'm' starts moving from the origin under the action of electric field, \( \vec{E}=E_{0}\hat{i} \) with a velocity \( v=v_{0}\hat{j} \). The time taken to increase its velocity to \( \frac{\sqrt{5}}{2} v_0 \) is:

\( 1\,\mu\text{C} \), \( -1\,\mu\text{C} \) charges are placed at a distance of 5 cm in forming a dipole. The amount of torque required to place this dipole perpendicular to an electric field of \( 3\times10^{5}~\text{NC}^{-1} \) is given by:

In the circuit shown in the figure, the current (I) is 6 A when \( R_{3} \) is infinite and current (I) is 9 A when \( R_{3} \) is short circuited. Then the values of \( R_{1} \) and \( R_{2} \) are respectively:

As shown in the figure two capacitors \( C_{1} \) \& \( C_{2} \) each having same gap between the plates x filled with different media of dielectric constants 3K and 6K respectively. If these two capacitors are connected to a battery, the ratio of potential differences across dielectric layers of \( C_{1} \) and \( C_{2} \) is:

The net outward flux through surface of a box is \( 8.0\times10^{3}~\text{Nm}^{2}\text{C}^{-1} \). The net charge inside the box is (approximately):

The current \( I_{3} \) in the given circuit is:

A compound microscope consists of an objective lens of focal length \( f_{o}=1~\text{cm} \) and an eyepiece of focal length \( f_{e}=5~\text{cm} \). An object is placed 1.2 cm in front of the objective. The final image is formed at the least distance of distinct vision. The nature of the intermediate image and the total magnification of the microscope are:

How fast a person should drive his car so that the red signal of light appears green? (wavelengths of red and green colours are 6200 and 5400 respectively)

A sound source of 1000 Hz frequency approaches the observer with speed \( 20~\text{ms}^{-1} \). The observed frequency of sound is nearly: (speed of sound in air \( = 340~\text{ms}^{-1} \))

The ratio of velocity of sound to the rms velocity of gas molecules in a diatomic gas is:

An ideal gas is taken through the cycle \( A\rightarrow B\rightarrow C\rightarrow A \) as shown in figure. If the net heat supplied to the gas in the cycle is 10 J, the work done in the process \( C\rightarrow A \) is:

Internal energy of an ideal gas depends only on:

A spherical perfect black body of radius 10 cm is maintained at \( 727^{\circ}C \). The total power radiated from it is (approximately) Stefan-Boltzmann constant, \( \sigma=5.67\times10^{-8} \, Wm^{-2}K^{-4} \)

If a person cannot see objects closer than 100 cm, the power of lens required to read at 25 cm is:

The equation of motion of a particle executing simple harmonic motion is given by \( X=\sqrt{2} [1.2 \sin 2t - 1.6 \cos 2t] \), where \( X \) is displacement in metre and \( t \) is time in second. The velocity of the particle at a time of 0.125 s is:

If the minimum time taken by a particle executing simple harmonic motion to move from extreme position to a point at a displacement of 86.6% of the amplitude is T, then the minimum time taken by the particle to move from mean position to a point at a displacement of 86.6% of the amplitude is:

A body cools from \( 80^{\circ}C \) to \( 50^{\circ}C \) in 5 min. Calculate the time it takes to cool from \( 60^{\circ}C \) to \( 30^{\circ}C \) if the surrounding temperature is \( 20^{\circ}C \)

A uniform metal wire is suspended from a rigid ceiling and a solid sphere is attached to the second end of the wire. If the radius of the sphere is doubled and then immersed in a liquid whose density is 60% of the density of the material of the sphere, then the percentage increase in the elongation of the wire is:

If a body is thrown vertically upwards from a height of 0.5 R (R is the radius of the earth) with a velocity equal to the escape velocity of a body from the surface of the earth, then the velocity of the body when it escapes from the gravitational influence of the earth is: (g is the acceleration due to gravity on the surface of the earth)