Search, filter, and study UPSC Civil Services & IFoS Physics past year questions with rigorous derivations, formulas, and step-by-step solutions.
Buy PYQ Solution Manual →
Alpha particles of velocity v enter a uniform magnetic field in perpendicular direction. If electrons of the same velocity v enter the same magnetic field the same way compare: (i) the curvatures of their path and (ii) the tracks they would show in (say) a bubble chamber.
Write down Plank's law of radiation and establish Wien's law from it.
Show that the electric field intensity due to any distribution of charges at rest can be expressed as the gradient of a potential. What is the relation between potential and potential energy? A thin disc of radius R is uniformly charged, \sigma being the charge per unit area. Find the potential and the electric intensity at points on the axis of the disc. How do these change as one crosses the disc? Explain the changes physically.
Set up the equation for the discharge of capacitor C connected in series with a resistor R and an inductor L. If R_0 stands for 2(L/C)^{1/2}, discuss three cases: R < R_0, R = R_0 \text{ and } R > R_0 What will you observe if the discharge takes place at low temperature when the material of resistor has become superconducting?
The components of an electrostatic field in vacuo are given as E_x = \frac{a}{r^3} + \frac{bx^2}{r^5} E_y = \frac{cxy}{r^5} E_z = \frac{fxz}{r^5} where a,b,c, and f are constants x,y,z, the rectangular cartesian coordinates and r^2=x^2+y^2+z^2. Using the basic equations obeyed by the electrostatic field in vacuo, find he relations between a,b,c and f and determine the charge density at a general point in space. Would that explain the observed field?
Starting from Biot-Savart law, calculate the magnetic field at the centre of a solenoid of length 1 meter, radius 2 cm and having 25 turns per centimeter, the current through the solenoid being 1 ampere.
Write a brief scientific note on Ferrimagnetism and ferrites.
A circular coil of wire having 100 turns and radius 10 cm is rotating about a vertical axis in its own plane uniformly at rate of 480 revolutions per minute. There is a horizontal magnetic field of intensity 0.01\text{ Wb/m}^2. The terminals of the coil are connected to the ends of an inductor having inductance 0.01 henry. Assuming that the resistance in the circuit can be neglected, find the current in the circuit at the instant the plane of the rotating coil is perpendicular to the magnetic field.
Define solar constant and say which of the values 1.34\text{ W/m}^2, 1.34 \times 10^3\text{ W/m}^2, 1.34 \times 10^5\text{ W/m}^2 is valid for it. Calculate the total energy radiated by the sun in one second and hence the decrease in its mass per second.
A charged particle moving horizontally towards the east with a velocity of 10^{5}\text{ m/s} enters into a region where there is a horizontal electric field E intensity 100\text{ volt/cm} directed towards the north as also a magnetic field B. The particle continues to move in the same direction as before. What can you san about the field B? Is it completely determined? What will be the path, of particle if the magnetic Field be switched off?
An electromotive force p_0 \sin pt + E_1 \sin 2 pt is impressed on a circuit containing an inductor and a resistor. Set up the differential equation obeyed by the current and show that in the steady state the current comprises two sinusoidal terms. Calculate the average power dissipation in the circuit. What is the difference, if any, between a varying current and an alternating current?
Write a short note on Wien's Law.
Three point charges are situated at the vertices of an equilateral triangle (one at each vertex); Show that the electric intensity vanishes at the centroid if and only if the charges are equal in magnitude and of the same sign.
Two point charges each of magnitude +2\text{ millicoulomb} are at A and B in front of a infinite conducting plane which is grounded. The line OAB is the perpendicular to time plane with the point O on the plane. If \mathrm{OA}=1\text{ m} and \mathrm{OB}=2\text{ m} calculate the force on the charge at A
Write down Maxwell's equations in vacuum. Show that in the source-free case, both the electric and magnetic vectors obey wave equations of identical form and considering a plane wave solution, prove dial the electric and magnetic vectors and the direction of propagation are mutually perpendicular. Show further that there is a propagation of energy given by the Poynting vector.
A wire of length l is bent into the form of a rectangle of side a and b and carries a current I. Calculate the magnetic field intensity at the centre of the rectangle. Show further that the intensity is minimum for a = b.
Discuss briefly the various ways of modulation of electromagnetic waves for the purpose of communication through radio and television.
State Kirchoff's laws for the distribution of currents (a) in the usual form for steady currents and (b) in a form applicable to alternating current networks. Discuss the method for comparing inductances by using Maxwell's bridge. State the disadvantages of the method.
Write down the expression for energy distribution of a black- body radiation at temperature T and deduce Wien’s displacement law.
A 220\text{ volt}, 50\text{ cycle}, supply is connected to a circuit containing a resistance of 20\text{ ohms} in series with a 100\mu\text{F} capacitor. Determine the current and the phase.