List of top Physics Questions

An electromagnetic wave travels along the z-axis. At a certain point in space, the electric field is \( 8.7 \, \text{Vm}^{-1} \) along the x-axis. What is the magnitude of the magnetic field along the y-axis?
A beam of light with intensity \( 10^5 \, \text{Nm}^{-2} \) and cross-sectional area \( 20 \, \text{cm}^2 \) is incident on a fully reflective surface at an angle of \( 45^\circ \). Find the force exerted by the beam on the surface.
For a hydrogen atom, the energy of a stationary electron is given by \( E_n = -\frac{13.6}{n^2} \, \text{eV} \). The energy required to excite the electron to the second excited state and to the ionized state are:
If the average power per unit area delivered by an electromagnetic wave is \( 9240 \, \text{Wm}^{-2} \), what is the amplitude of the magnetic field in the wave?
A coil of inductance \( 0.1 \, \text{H} \) and resistance \( 110 \, \Omega \) is connected to an AC source of \( 110 \, \text{V}, 350 \, \text{Hz} \). What is the phase difference between the voltage maximum and the current maximum?
The metal which has the highest work function in the following is:
Two positive charges of 10 \( \mu \text{C} \) and 12 \( \mu \text{C} \) are 10 cm apart. What is the work done in bringing them 6 cm closer?
Two infinite wires are placed at \( x = -2 \, \text{cm} \) and \( x = 1 \, \text{cm} \) along the y-axis, each carrying current upward. An electron is fired from the origin at \( 45^\circ \) to the x-axis with speed \( U \). The force on the electron at the moment of launch is:
(\( B_0 \) is the field at origin due to the wire at \( x = 1 \, \text{cm} \))
Two electrons \( e_1 \) and \( e_2 \), both having mass \( m \) and charge \( q \), are projected perpendicular to a magnetic field \( B \). If the kinetic energy of \( e_1 \) is twice that of \( e_2 \), what is the relation between their rotation frequencies \( f_1 \) and \( f_2 \)?
A compass needle oscillates 20 times per minute at a location with dip \( 45^\circ \) and magnetic field \( B_1 \). It oscillates 30 times per minute at another location where dip is \( 30^\circ \) and field is \( B_2 \). Find the ratio \( \frac{B_1}{B_2} \).
Current density in a cylindrical wire of radius \( R \) varies with radial distance as \( \beta (r + r^2) \). What is the current through the shaded section (sector angle \( \pi/6 \)) of the wire as shown in the figure?
Current density in a cylindrical wire of radius R
A cell supplies currents of 1 A and 0.5 A through resistors of 2.5 \( \Omega \) and 10 \( \Omega \), respectively. The internal resistance of the cell is:
A capacitor \( C_1 = 1\, \mu\text{F} \) is charged using a 9 V battery. It is then disconnected and connected to capacitors \( C_2 = 2\, \mu\text{F} \) and \( C_3 = 3\, \mu\text{F} \) as shown. Find the charge on \( C_3 \) after equilibrium is reached.
A capacitor C1 = 1µF is charged using a 9 V battery
An electric dipole with dipole moment \( 5 \times 10^{-7} \, \text{Cm} \) is in an electric field of \( 2 \times 10^4 \, \text{NC}^{-1} \) at an angle of \( 60^\circ \) with the direction of the field. The torque acting on the dipole is:
A ray is incident from a medium of refractive index 2 to another with refractive index 1. The critical angle is:
A Carnot engine operates between a source and sink. The efficiency of the engine is 40\% and the sink temperature is \( 27^\circ \text{C} \). If the efficiency is to be increased to 50\%, then by how much should the source temperature be increased?
A car engine has a power of 20 kW and runs for 1 hour. If the thermal efficiency is 40\% and ambient temperature is 300 K, then what is the energy generated by fuel combustion?
The number of vibrational degrees of freedom for a diatomic molecule is:
A body is suspended from a string of length 1 m and mass 2 g. The mass of the body required to produce a fundamental frequency of 100 Hz in the string is (Take \( g = 10 \, \text{ms}^{-2} \))
Electrostatic force between two identical charges placed at a distance \( r \) is \( F \). A slab of width \( \frac{r}{5} \) and dielectric constant 9 is inserted between them. Then, the new force between the charges is:
Consider the following statements:
(A) Whentemperature increases, the viscosity of gases increases and viscosity of liquids decreases.
(B) Water does not wet an oily glass because the cohesive force of oil is less than that of water.
(C) A liquid will wet a surface if the angle of contact is greater than 90◦.
Which of the following is true?
Same tension is applied to four wires made of the same material. The elongation is maximum in which wire?
A hydrometer executes SHM when pushed into a liquid of density \( \rho \). If the mass of hydrometer is \( m \) and the radius of the tube is \( r \), then the time period of oscillation is:
A projectile is thrown straight upward from the earth’s surface with an initial speed \( V = \alpha V_E \), where \( \alpha \) is a constant and \( V_E \) is the escape speed. The projectile travels up to a height 800 km from the earth’s surface, before it comes to rest. The value of the constant \( \alpha \) is:
(Take radius of the earth \( R = 6400\, \text{km} \))
A sphere of surface area \( 4 \, \text{m}^2 \), temperature 400 K, emissivity 0.5 is in an environment of 200 K. The net rate of energy exchange is (take \( \sigma = 5.67 \times 10^{-8} \, \text{Wm}^{-2} \text{K}^{-4} \))