Class 12 Physics Board Exam Question 2079- SET O

NEB – GRADE XII

2079 (2022)
Physics
New Course
Sub. Code: 1021 ‘0’

For regular students (except technical stream)

Candidates are required to give their answers in their words as far as possible. The
figures in the margin indicate full marks.

Time: 3 hrs. Full Marks: 75
Attempt all the questions

GROUP A [11×1=11]

Rewrite the correct options of each question in your answer sheet

1. In rotational motion, the quantity that imparts angular acceleration is:
A) Force

B) Torque

C) Moment of Inertia

D) Angular Momentum

2. Two identical springs are arranged with a block as in figure. The oscillation frequency of the mass is f. if one spring is removed, the frequency of the oscillation will be
A) f

B) 2f
C) √2f

D) f√2

3. A liquid does not wet the surface of a solid if angle of contact is,
A) 90 ̊

B) less than 90 ̊

C) greater than 90 ̊

D) 0 ̊

4. Identify the wrong statement
A) For isothermal process, ∆T=0
B) For isochoric process, ∆V=0
C) For isobaric process, ∆P=0
D) For cyclic process, ∆W=0

5. The maximum efficiency of an engine operating between 30 ̊C and 300 ̊C is
A) 4.71%

B) 47%

C) 90%

D) 9%

6. In which frequency range the infrasonic wave lies?
A) (10-20) Hz

B) (30-40) Hz

C) (20-30) Hz

D) (50-60) Hz

7. In Fraunhofer diffraction, the incident wavefront should be
A) Elliptical

B) plane

C) spherical

D) cylindrical

8. If specific resistance of a potentiometer wire is 10−7Ωm, current flowing through it is 0.1A and cross-sectional area of wire is 10−6m2, then potential gradient will be
A) 10−2V/m

B) 10−4V/m

C) 10−6V/m

D) 10−8V/m

9. A coil having N number of turns and cross-sectional area A carries a current I. the quantity NIA is
A) Magnetic flux

B) magnetic field
C) magnetic susceptibility

D) magnetic moment

10.At resonance, in series LCR circuit, which relation does not hold good

A) ω =1/√LC
B) Lω =1/Cω
C) Cω =1/Lω
D) ω =1/LC

11.Which of the following is correct?
A) E² = P²C

B) E² = P²C²

C) E² = PC²

D) E² = P²/C²

GROUP B [8×5=40]

12.The angular speed is inversely proportional to the moment of inertia, that is given by principle of conservation of energy. [1+2+2]
a. In a flywheel, most of the mass is concentrated at the rim? Explain why.
b. The angular velocity of the earth around the sun increases when it comes closer to the sun. why?
c. If the earth were to shrink suddenly, what would happen to the length f the day?

13.Simple harmonic motion is defined from periodic functions like sine or cosine functions.
a. State the basic equation of motion for a body executing simple harmonic motion. [1]
b. Find expression for velocity and acceleration of a describing SHM. [2]
c. The tip of tuning fork goes through 550 complete vibrations in 1 sec. find the angular frequency and time period of the motion. [1+1=2]

OR

a. Define surface tension. [1]
b. State Bernoulli’s theorem. [1]
c. Castor oil at 20 ̊C has a coefficient of viscosity 2.42 Ns/m²and density 940 kgm-3. Calculate the terminal velocity of a steel ball of radius 2mm falling under gravity in the oil, taking the density of steel as 7800kg/m3.(g = 10m/s2) [3]

14.Adiabatic process:
a. Define adiabatic process in thermodynamics. [1]
b. Derive expression for work done during adiabatic process. [3]
c. Write the mathematical expression of entropy. [1]

15.a. Define an organ pipe. [1]
b. Describe the various modes of vibration of the air column in a closed organ pipe. [3]
c. What is end correction? [1]

a. State Doppler’s effect. [1]
b. Derive the apparent frequency of sound when an observer moves towards
a stationary source. [2]
c. A stationary motion detector sends sound waves of 150 KHz towards a truck approaching at a speed of 120km/hr. What is the frequency of wave reflected back to detector? (Velocity of sound in air = 340m/s) [2]

16.a. Differentiate Seebeck’s effect and Peltier’s effect. [2]
b. Explain the variation of thermo-emf with temperature. [3]

17.When a charge particle moves in a uniform magnetic field, it experiences a force, called the Lorentz force.

a. What is the vector representation of Lorentz force? [1]
b. State Fleming left hand rule. [1]
c. A horizontal straight wire 5 cm long weighing 1.2gm−1 is placed perpendicular to a uniform horizontal magnetic field of flux density 0.6T. if the resistance of the wire is 3.8Ωm−1 , calculate the p.d. that has to be applied between the ends of the wire to make it just self-supporting. [3]

18.Electron is deviated in electric and magnetic field.
a. What path does the electron follow in electric field when the electron is projected normally in the field? [1]
b. An electron passes through a space without deviation. Does it mean there is no field? [2]
c. Is there any condition that an electron does not experience any force inside the magnetic field? [2]

19.a. What is rectification? [1]
b. Explain rectifier circuit operation with two diodes. [3]
c. What happens when one of the diodes becomes functionless?[1]

GROUP C [8×3=24]

20.a. Write sustainable conditions for interference. [2]
b. “The bright and dark fringes are equally spaced.” Justify this statement from Young’s double slit experiment. [3]
c. In a Young’s double slit experiment, the separation of first to fifth fringes is 2.5 mm when the wavelength used is 620nm. The distance from the slits to the screen is 80 cm. Calculate the separation of two slits. [3]

21.Kirchhoff’s laws in electricity are very useful in solving in solving the
complicated circuit connections.
a. What is the significance of first law? [1]
b. State and explain second law with circuit diagram. [2]
c. Apply these laws to calculate unknown value of resistance. [3]
d. What is meter bridge? Write name of material used to construct meter bridge. [1+1=2]

OR

a. Derive the expression for impedance in L-C-R circuit. [3]
b. Find the condition of resonance L-C-R circuit. [2]
c. A circuit consists of a capacitor of 2μF and a resistor of 1000Ω. An alternating emf of 12V (rms) and frequency 50Hz is applied. Find the current flowing, the voltage across capacitor and the phase angle between applied emf and current. [3]

22.a. State Bohr’s postulate of atomic model. [2]
b. Derive an expression for radius of nth orbit in H-atom. [3]
c. Calculate de Broglie wavelength of electron when it is accelerated by 500 Volt. (mass of electron = 9.1 × 10−31 kg, Plank’s constant = 6.62 × 10−34 Js, charge of electron = 1.6 × 10−19 C) [3]

OR

Radioactivity is the spontaneously occurring phenomenon in nature.
a. What is radioactivity? [1]
b. Obtain N = Noe−λt in radioactive decay law. [3]
c. Describe the significance of decay curve showing the longest life time of radio-isotopes. [1]
d. The half-life of radium is 1620 years. After how many years 25% of a radium block remains undecayed? [3]