List of top Physics Questions asked in UP Board XII

Equivalent resistance of three identical resistors in series is \( R_1 \) and in parallel it is \( R_2 \). If \( R_1 = nR_2 \), then the minimum possible value of \( n \) is:
Write down the relationship between root-mean-square value and peak value of an alternating voltage. In the given circuit, find the value of inductive reactance and the potential difference between the ends of the resistance.

A plane electromagnetic wave represented as \( E = 100 \cos (6 \times 10^8 t + 4x) \, \text{V/m} \), is propagated through a medium of refractive index:
State Gauss's theorem of electrostatics. What is the meaning of equipotential surface? Two insulator plates having equal charge density are placed as shown in the figure. Find the electric field intensity at points P and Q.
Stating Huygens' principle of secondary wavelets, throw light on its success and failure. Draw the wavefront of light emerging from a convex lens due to a point source of light placed on its focus.
What is the meaning of interference? Derive the expression for the intensity of the resulting wave due to interference of the waves \( y_1 = a_1 \sin(\omega t) \) and \( y_2 = a_2 \sin(\omega t + \phi) \). If \( a_1 = 5 \, \text{cm} \) and \( a_2 = 3 \, \text{cm} \), then find the ratio of maximum and minimum intensities of the resulting wave.
Draw a ray diagram for an astronomical telescope when the final image is formed at infinity. A building of height 100 m and at a distance of 2 km is seen through this telescope. Then what will be the height of the image formed by the objective of the telescope? Focal length of the objective is 150 cm.
Give the relationship of temperature with the resistance and resistivity of a conductor. Define the temperature coefficient of the resistance and give its unit.
Explain the principle of potentiometer. Why is it superior to a voltmeter? How will you compare the e.m.f. of two cells by potentiometer? Explain by drawing a relevant circuit diagram.
What is the photoelectric effect? For any photosensitive surface, the threshold frequency is \( 3.3 \times 10^{14} \, \text{Hz} \). If the frequency of incident light becomes \( 8.2 \times 10^{14} \, \text{Hz} \), then calculate the stopping potential and give the value of the work function of the surface also.
What is the photoelectric effect? For any photosensitive surface threshold frequency is \( 3.3 \times 10^{14} \, \text{Hz} \). If frequency of incident light becomes \( 8.2 \times 10^{14} \, \text{Hz} \), then calculate the stopping potential and give the value of work function of the surface also.
What are light emitting diodes? Describe the principle and working of a light emitting diode. Why are they more useful than traditional filament lamps?
Define electric dipole and dipole moment. An electric dipole of dipole moment \( 2 \times 10^{-8} \, \text{C} \cdot \text{m} \) is inclined at an angle of 30° from a uniform electric field of \( 2 \times 10^5 \, \text{V/m} \). Find the potential energy of the dipole and the moment of the couple acting on it.
Diameter of two spheres of metal are 6 cm and 4 cm. They are charged to the same potential. Find out the ratio of the surface densities of charge on the sphere.
How can the capacity of a conductor be increased? Radius of the plates of a parallel plate air capacitor is \( 3 \times 10^{-2} \, \text{m} \) and the capacitance is equal to the capacitance of a charged sphere of radius 1 m. Find the distance between the plates of the capacitor.
Write lens maker's formula for a thin lens. On its basis, discuss the effect of refractive index of lens material and radius of curvature of lens surfaces on its focal length.
Write down the definition of coefficient of self-induction and coefficient of mutual induction. Current of 5 A decreases to zero in 0.1 s in a coil of 5 H self-inductance. Find out induced e.m.f. produced in the coil.
The wavelength of light incident on a metal surface of work function 2.14 eV is 5000 \(\overset{\text{\small o}}{\text{A}}\). Find the maximum kinetic energy and the maximum velocity of the emitted photoelectrons.
Draw a circuit diagram of a transistor amplifier in common emitter configuration and explain its working in brief.
What is a transformer? Describe the energy losses occurring in a transformer.
Explain transverse nature of electromagnetic waves. Give a brief description of the uses of radio waves.
Write down the difference between the chain reaction occurring in nuclear bombs and nuclear reactors.
What is meant by the binding energy of a nucleus? If mass defect for a nucleus is \( 10^{-6} \, \text{kg} \), then find its binding energy in electron volt.
Give the definition of isotopic and isobaric nuclei and mention the difference between them.
On the basis of Ampere's circuital law, find the expression for the magnetic field produced by an infinitely long straight current-carrying conductor.