List of top Physics Questions

Two amplifiers are connected one after the other in series (cascaded). The first amplifier has a voltage gain of 10 and the second has a voltage gain of 20. If the input signal is 0.01 Volt, calculate the output AC signal.
The rate of a radioactive disintegration at an instant is \( 10^8 \, {s}^{-1} \). The half-life of the radioactive sample is \( 3.3 \times 10^{12} \, {s} \). The number of radioactive atoms present in the sample at that instant of time is
The ratio of kinetic energy to the total energy of an electron in a Bohr orbit of a hydrogen atom is
In a series LCR circuit, the voltage across resistance of \( 2000 \, \Omega \) is 200 V and the resonant frequency is \( 400 \, {rad/s} \). The capacitance \( C \) value is 4 μF. At resonance, the voltage across \( L \) is
A helicopter has metallic blades with length 4 m extending outward from the central point and rotating at 3 rev/s. If the vertical component of Earth's magnetic field is 40 µT, then the emf induced between the blade tip and the central point is
“Introduction of a small charged sphere into a larger one allows us to keep piling up a larger and larger amount of charge on the latter” – This is the principle of the:
A parallel plate capacitor has two plates of area 'A' separated by distance 'd'. The capacitor is charged to a potential difference 'V' and the battery is disconnected. A metal plate with area 'A' and thickness \( \frac{d}{2} \) is inserted between the plates, so that it is always parallel to the plates. The work done on the metal slab while it was inserted is:
A gas with a ratio of specific heats, \( \gamma = \frac{4}{3} \), is heated isobarically. The percentage of the given heat used in external work done is
A U-tube is partially filled with water. Oil which does not mix with water is next poured into one side of the U-tube until entire water rises by 25 cm on the other side. If the density of oil is 0.8 g cm\(^{-3}\), the oil level will stand higher than the water level by:
A torque of 10 Nm is applied on a wheel having angular momentum of 2 kg m\(^2\) s\(^{-1}\). The angular momentum of the wheel after 4 s is:
A ball strikes a horizontal floor at 45°. If 25% of its kinetic energy is lost in the collision, then the coefficient of restitution is:

The relation between velocity \( V \) (in ms\(^{-1}\)) and the displacement \( x \) (in meters) of a particle in motion is \( 2V = \sqrt{37 + 32x} \). 
The acceleration of the particle is 
 

For an amplitude modulated wave, the maximum and minimum amplitudes are respectively 16 V and 4 V. The modulation index is:

Three logic gates are connected as shown in the figure. If the inputs are \(A = 1\), \(B = 0\) and \(C = 0\) then the values of \(y_1\), \(y_2\) and \(y_3\) respectively are: 


 

One ring, one solid sphere, and one solid cylinder are rolling down on the same inclined plane starting from rest. The radius of all three are equal. The object that reaches down with maximum velocity is
The work done on a wire of volume \( 2 \) cm\(^3 \) is \( 16 \times 10^2 \) J. If the Young's modulus of the material of the wire is \( 4 \times 10^{12} \) Nm\(^{-2} \), then the strain produced in the wire is
A uniform metal solid sphere is rotating with angular speed \( \omega_0 \) about its diameter. If the temperature is raised by 50°C, the angular speed will be: Given \( \alpha_{\text{metal}} = 20 \times 10^{-5} \, \text{°C}^{-1} \)
The work function of a photosensitive metal surface is \(6.4 \times 10^{-19} \, {J}\). The maximum kinetic energy of the emitted photoelectrons when electromagnetic radiation of wavelength 1240 Å incidents on the metal surface is nearly:
A resistor of resistance \( R \), an inductor of inductive reactance \( 2R \), and a capacitor of capacitive reactance \( 3R \) are connected in series to an ac source. The power factor of the series LCR circuit is:
A pair of adjacent coils has a mutual inductance of 80 mH. If the current in one coil changes from 10 A to 25 A in a time of 1.5 s, the change of flux linked with the other coil is:
A wire of length 100 cm is bent in the form of a circular coil of 5 turns and another wire of length 60 cm is bent in the form another circular coil of 4 turns. If the same current flows through the two coils, then the ratio of the magnetic fields induced at the centres of the two coils is:
Two separated conducting spheres \(S_1\) and \(S_2\), of radii \(3R/4\) and \(R/4\) having \(15 \mu C\) and \(-3 \mu C\) charges respectively are at a large distance. They are now connected by a conducting wire. After a long time, the charges on \(S_1\) and \(S_2\) respectively are:
A 200 volt battery is connected across the series combination of two capacitors 4 \(\mu\)F and 6 \(\mu\)F. The amount of energy stored in this series combination is:
A geyser uses natural gas as fuel. It heats water flowing at the rate of 3.0 liters per minute from 27°C to 77°C. The approximate rate of consumption of the fuel, if the heat of combustion of gas fuel is \(4.0 \times 10^4 { J/g}^{-1}\):

Helium gas goes through a cycle ABCDA (consisting of two isochoric and isobaric lines) as shown in figure. Assuming the gas to be an ideal gas. Efficiency of this cycle is nearly: