**DEVI SECONDARY SCHOOL ****Sub Code: 1011**

**Birtamod-5, Jhapa**

**Final Examination-2078**

**Class : XI Time : 3 hrs**

**Subject : Physics FM : 75**

*[Candidates are required to give their answer in their own words as for as practicable the figure on the right side indicates full marks.]*

__Group ‘A’__

**Choose the best alternative to the following questions. (1×11=11)**

#### 1. Which of the following have same dimension?

a. Angular momentum and linear momentum b. Work and power

c. Work and Torque d. Torque and pressure

**2. The maximum number of components of a vector that can be splitted are….**

a.2 b. 3 c.4 d. infinite

**3. A particle moving in a circle with a uniform speed has constant…..**

a. Velocity b. acceleration c. Kinetic energy d. displacement

**4. The acceleration due to gravity at the ****equator**** is g. its value at the pole is…..**

a. less than at equator b. greater than g c. less than g d. none of the above

**5. The deviation produced by a prism doesn’t depend on…..**

a. Angle of prism b. Material of prism c. The angle of incidence d. Size of the prism

**6. Which of the following remains constant during refraction?**

a. Velocity b. Wavelength c. Amplitude d. Frequency

**7. In the formation of a rainbow, the light from the sun on water droplets undergoes which of the following phenomenon phenomena?**

a. dispersion only b. only total reflection c. dispersion and total internal reflection d. scattering

**8. what is the power of a lens whose focal length is 0.5 m ?**

a. 1 D b. 0.5 D c.2 D d. 2.5 D

**9. Holes are majority charge carriers in……….**

a. N-type semiconductors b. ionic solids c**. **P-type semiconductors d. metals

**10. The capacitance of a parallel plate capacitor increases with…….**

a. decrease of its area b. increase of its distance c. increase of its area d. none of above

**11. current in a ****metallic**** conductor is due to………**

a. flow of electrons b. flow of ions c. flow of electrons and ions both d. flow of molecules.

__Group ‘B’__

**Answer the following questions. (8×5=40)**

- a. Find the angle of projection at which the range the horizontal range and maximum height of projectile are equal. [2]
- An object is dropped from the top the tower of height 156.8 m and the same time another object is thrown vertically upward with the velocity of 78.4ms
^{–1}from the foot of the tower, when and where the two objects meet? [3]

14. a. Which physical property of molecules of a gas gives a measure of temperature? [1]

b.A steel wire 8m long and 4 mm in diameter is fixed to two rigid supports. Calculate the increase in tension when the temperature falls by 10^{0}C. Given linear expansivity of steel, = 12×10^{-6}/K, Young’s modulus for steel, Y = 2×10^{11} N/m^{2}. [3]

c. Define temperature gradient in an object. [1]

15. a. Why do we prefer white colored clothes in summer and black colored clothes in winter? [2]

b. A slab of stone of area 0.36m^{2} and thickness 10cm is exposed on the lower surface to steam at 10^{0}C. A block of ice at 0^{0}C rests on the upper surface of the slab. In one hour 4.8 kg of ice is melted. Calculate the thermal conductivity of stone.

[Latent heat of fusion ice = 3.36×10^{5}J/kg] [3]

16 a. “A concave mirror is called converging mirror. Why? [1]

b. State one daily application of convex Mirror. [1]

c.A ray of light is incident at 60° in air on an air-glass plane surface. Find the angle of refraction in the glass (µ for glass = 15). [3]

**or**

a. Define principal focus. Why is it called so? [2]

b. i. Define power of lens [1]

ii. The radii of curvature of double concave lens are 30 cm and 60 cm. The refractive index of its glass is 15 Calculate the focal length of the lens. [2]

**17.a. What is meant by quantization of charge? [1]**

b. Describe the effect of permittivity on force between two charges. [2]

“Nothing happens to a bird standing on high power line but a man gets fatal shock by touching to it”, why? [2]

**18. a. How will you arrange 3 capacitors each having the capacity of 2F, to get a capacitor of capacity 3F? [2] **

b. Two horizontal parallel plates, each of area 500 cm^{2} are mounted 2 mm apart in a vacuum. The lower plate is earthed and the upper one is given a positive charge of 0.05 C. Deduce values for

i. the capacitance between the two plates and

ii. electrical energy stored in the system [3]

**19. a. A wire is stretched to double its length. What happens to its resistance and resistivity? [2]**

b. a potential difference of 4.5v is applied between the end of a wire that is 2.5 m long and has radius of 0.654mm. The resulting current through the wire is 17.6A . what is the resistivity of the wire ?

__Group ‘C’__

**Given long answer in the following questions. [3×8=24]**

**a. Why is it easier to hold down a 10 kg body in your hand at your side than to hold it with your arm extended horizontally?**[2]

b. A 550 N physics student stands on a bathroom scale in an elevator. As the elevator starts moving, the scale reads 450N.

i. Find the acceleration of the elevator (magnitude and direction). [2]

ii. What is the acceleration if the scale reads 670N? [2]

c. What is the difference between center of gravity and center of mass of a system? [2]

**21. a. Derive an expression for the energy stored in stretched wire. Define the term energy density of a body under strain. [3]**

b. What is the percentage increase in the length of a wire of diameter 2.5 mm stretched by a force of 100 kg? Young’s modulus of elasticity of the wire is 12.5 × 10^{11} dyne cm^{–2}. [3]

c. Iron is more elastic than rubber. Why? [2]

**Or**

a. Differentiate conservation of kinetic energy and conservation of linear momentum. [2]

b. Show that the relative velocity of approach before collision is equal to the relative velocity of separation after collision. [3]

c. Derive an expression for the banking angle. [3]

**22. a. Define atomic mass unit and convert it into MeV. [2]**

b. The energy liberated in the fission of a single atom of uranium – 235 is 3.2 × 10^{-11} J. Calculate the power production corresponding to the fission of 1gm of uranium per day.

(Assume Avogadro constant = 6.0 × 10^{23} mole^{-1}). [3]

c. What is the difference between intrinsic and extrinsic semiconductors? [2]

**– The end –**