NEB Class 12 Science Physics Question Paper 2080 (Set A)

The moment of inertia of a body of mass M about a given axis is I. What is the radius of gyration?

The maximum velocity and maximum acceleration of a particle executing SHM are 4 m/s and 2 m/s² respectively. Its time period of oscillation is

A spherical ball is dropped into a long column of a viscous liquid. The speed (v) of the ball as a function of time (t) may be best represented by

• A)
• B)
• C)
• D)

In which of the following processes of the gas, work done is the maximum?

When the door of a refrigerator is left open in a room, the temperature of the room.

Distance between two consecutive nodes in a standing wave is

The critical angle of a certain medium is $\sin^{-1}\left(\dfrac{3}{5}\right)$. Then the polarizing angle of the medium will be

The value of magnetizing field (H) when magnetic flux density equals to zero (B=0) is called

In our country, the supply of a.c. voltage is 220 V. The peak voltage is

A long solenoid carrying a current produces a magnetic field 'B' along its axis. If the current is doubled and the number of turns per cm is halved, then new value of magnetic field is

Which of the following earthquake waves is first recorded on the seismograph?

a) Define simple harmonic motion. (1)

b) Derive an expression for total mechanical energy of a particle executing simple harmonic motion. (3)

c) Show graphically, how the kinetic energy, potential energy and total energy of the particle vary with displacement from its equilibrium position. (1)

a) What is meant by surface energy of a liquid? Write its relation with surface tension of the liquid. (2)

b) An air bubble of radius 1 cm is rising at a steady rate of 5 mm/s through a liquid of density 0.8 g/cm³. Calculate the coefficient of viscosity of the liquid. (Neglect the density of air) (3)

a) Draw a PV diagram of a petrol engine and explain its working based on the PV diagram. (3)

b) Why is Cp always greater than Cv? Explain. (2)

a) What is Doppler's effect? Calculate the apparent frequency when a source moves towards a stationary observer. (1+2)

b) Why sound waves are also called pressure waves? Explain. (2)

a) State Lenz law in electromagnetism. Does this law violet the principle of conservation of energy? Explain. (3)

b) In figure, a magnet is moving towards one end of a solenoid connected to a sensitive galvanometer. During this movement, a current is induced in the solenoid. Does the direction of induced current change if the magnet is moved away from the solenoid? Explain. (2)

a) Define one Ampere of current in terms of the force between two parallel current carrying conductors. (1)

b) How do you explain the contraction of the solenoidal coil while the current is passed through it? (1)

c) A horizontal straight wire of mass 0.12 gm and length 10 cm is placed perpendicular to a uniform horizontal magnetic field of flux density 0.6 T. If the resistance per unit length of the wire is 3.8 Ω m⁻¹, calculate the potential difference that has to be applied between the ends of the wire to make it just self-supporting. (3)

OR

a) What do you mean by Seebeck effect? (1)

b) Explain the variation of thermo-emf with temperature of junction. (2)

c) In a given thermo-couple the temperature of cold junction is 25°C while the neutral temperature is 270°C. What is the value of temperature of inversion? (2)

a) What is meant by specific charge of an electron? It's value is constant for cathode rays but not for positive rays, why? (2)

b) A beam of electron is under the effect of potential difference 1.36×10⁴ volt applied across two parallel plates 4 cm apart and a magnetic field of 2×10⁻³ wb/m² at right angles to each other.

i) Calculate velocity of electrons if the two fields produce no deflection in the beam. (1)

ii) What will be the radius of the orbit in which the beam will move if the electric field is made zero? (2)

a) Define the terms: half life and decay constant of a radio active substance. (2)

b) In a given sample, two radio isotopes A and B are initially present in the ratio of 1:4. The half-lives of A and B are 100 years and 50 years respectively. Find the time after which the amounts of A and B become equal. (3)

OR

a) What characteristic of a junction diode is used in rectification? (1)

b) Explain the working of junction diode as full wave rectifier (2)

c) The output of two-input AND gate is fed to a NOT gate. Give its logic symbol and construct its truth table. (2)

a) What is the significance of the negative energy of the electron in an orbit? (1)

b) The diagram shows the lowest four discrete energy levels of an atom (n=1: -54.4 eV, n=2: -13.6 eV, n=3: -6.04 eV, n=4: ?). An electron in n=4 state makes a transition to n=2 state emitting a photon of wavelength 121.9 nm.

i) Calculate the energy level of n = 4th state. (1)

ii) Calculate the momentum of the photon. (1)

c) The photon is then incident on a silver surface in a photoelectric experiment and the surface emits an electron with maximum possible kinetic energy. If the work function of silver is 4.7 eV,

i) What do you mean by work function? (1)

ii) Calculate the maximum kinetic energy of the emitted electron. (1)

iii) Determine the stopping potential for the emitted electron. (1)

d) Calculate the de-Broglie wavelength of an electron accelerated through a potential difference of 2 kV. (Planck's constant, h = 6.62×10⁻³⁴ Js) (2)

a) Two narrow slits are illuminated by a single monochromatic source of light. Name the pattern obtained on the screen and explain how these patterns are obtained? (1)

b) One of these slits is now completely covered. Name the pattern obtained on the screen. (1)

c) Write the difference between the patterns obtained in the above two cases on the basis of Huygen's principle. (1)

d) Suppose a monochromatic light of wavelength 'λ' is incident normally on a narrow slit of width 'd' and focused on a screen. Derive condition for the first minimum of intensity on the screen in terms of wavelength λ and angle of diffraction 'θ'. (2)

e) A plane transmission grating has 500 lines per mm and the second order spectral line is refracted 30°. Calculate the wavelength of light used. (3)

OR

a) Define an open organ pipe (1)

b) Describe various modes of vibration air column in an open organ pipe. (3)

c) A musician tunes his guitar by turning the screws provided at the end, why? (2)

d) A steel wire of length 1m long has a mass 80gm and is stretched with a tension of 1000 N. Calculate the fundamental frequency of transverse vibration. (2)

a) State Kirchhoff's law for electrical circuits. (2)

b) Wheatstone Bridge is a good engineering of circuit designing which has several applications.

i) Draw Wheatstone Bridge circuit diagram. (1)

ii) State Wheatstone Bridge principle. (1)

iii) Use Kirchhoff's law to derive balanced condition for the Wheatstone Bridge circuit. (1)

c) What is thermoelectric effect? Discuss the variation of thermo-emf with the temperature of hot junction of a thermo-couple. (3)

Or

a) What is electrical resonance of series LCR circuit? (1)

b) Calculate resonant frequency of series LCR circuit. (2)

c) A series LCR circuit is as shown in the figure below (R = 8Ω, C = 800 μF, L = 300 nH, supply 220 V, 50 Hz).

i) Calculate impedance of the circuit (2)

ii) Current in the circuit. (1)

iii) Voltage across resistor R. (1)

d) What is meant by Wattless current? (1)