List of top Questions asked in UP Board XII

What are light emitting diodes? Describe the principle and working of a light emitting diode. Why are they more useful than traditional filament lamps?
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.
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.
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.
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.
Draw a circuit diagram of a transistor amplifier in common emitter configuration and explain its working in brief.
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.
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.
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.
Draw symbol of NOR gate and draw truth table for its output.
Write the formula for the momentum of a photon.
Write down the difference between the chain reaction occurring in nuclear bombs and nuclear reactors.
Equation of electric field of a plane electromagnetic wave is \( E_y = 60 \sin(500x - 1.5 \times 10^{11}t) \, \text{V/m} \). Write the equation for the magnetic field of the wave.
Write down the phase difference between voltage and current in a pure inductive alternating circuit.
e.m.f. of a cell is 1.5 volt and internal resistance is \( 0.1 \, \Omega \). On connecting the cell with an external resistance of \( 2.9 \, \Omega \), what will be the potential difference at the terminals of the cell?
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.
On the basis of Ampere's circuital law, find the expression for the magnetic field produced by an infinitely long straight current-carrying conductor.
Give the definition of isotopic and isobaric nuclei and mention the difference between them.
What is an oscillator? Explain the working of a transistor as an oscillator with a suitable circuit diagram.
Unit of electric flux is :
Sensitivity of moving coil galvanometer can be increased by :
Resistance of an ideal p-n junction in forward and reverse bias respectively will be :
True statement with reference to matter waves is :