# NEB-GRADE XI

## 2076 (2019)

## Physics

## Time: 3 hrs. Full Marks:75

## * Candidates are required to give their answers in their own words as far
as practicable.*

*Candidates are required to give their answers in their own words as far as practicable.*

**You may use the following values of physical constants wherever necessary:**

* Acceleration due to gravity (g) = 10ms ^{-2}*

* Young’s modulus for copper = 1.2×10 ^{ 11 } Nm ^{-2}*

* Young’s modulus for steel = 2×10 ^{ 11 } Nm ^{-2}*

* Cubical expansivity of glass = 1.2×10 ^{ -5 / o } C*

* Cubical expansivity of mercury = 18×10 ^{ -5 / o } C*

* Specific heat capacity of copper = 400 Jkg ^{-1 } k ^{ -1}*

* Specific heat capacity of water = 4200 Jkg ^{ -1 } k ^{ -1}*

* Ratio of molar heat capacities (Î³ ) = 1.4*

* Permittivity of free space (∈ _{o } ) =8.85×10 ^{-12 } C ^{2 } N ^{-1} m ^{-2}*

## Group ‘A’

** 1. Answer in brief, any six questions. 6×2=12**

- The energy of a photon is given by
*Î• = hf.*Find the dimension and unit of Plank’s constant*h*, where*f*is the frequency of radiation. - From a flying aeroplane a body should be dropped in advance to hit thetarget, why?
- A light body and a heavy body have the same momentum. Which one will have greater Kinetic energy? Explain.
- A person sitting in an artificial satellite of the earth feels weightlessness,but a person standing on moon has weight through the moon is a satellite of the earth. Why ?
- The passengers in a small boat are not allowed to stand, why ?
- If the ice on the polar caps of the earth melts, how will it affect the duration of the day? Explain.
- Why does hot soup taste better than cold soup?

** 2. Answer in brief, any two questions. 2×2=4**

- The latent heat of vaporization is much larger than the latent heat of fusion of a substance. Why?
- Why does it take longer time to dry wet clothes in rainy summer than insunny winter ?
- The internal energy of a compressed gas is less than that of a rarefied gas at the same temperature. Why?

** 3. Answer in brief, any one question. 2**

- The sun is less bright in morning and evening as compared to that atnoon although its distance from the observer is almost the same. Why?
- When white light is dispersed by a prism, red light appears at the top of the spectrum where as violet at the bottom. Why?

** 4. Answer in brief, any one question. 2**

- Bits of paper are attracted to an electrified comb, even though they have no net charge. How is this possible?
- Can two electric lines of force intersect each other? Explain.

## Group ‘B’

** 5. Answer any three questions. 3×4=12**

- What is escape velocity ? Derive an expression for it on the surface of the earth.
- Define angle of friction and angle of repose. Establish a relation between them.
- Define moment of inertia. Derive an expression for the moment of inertia of thin uniform rod about an axis through its centre and perpendicular to its length.
- What is simple harmonic motion ? Calculate the total energy of a particle executing simple harmonic motion.

** 6. Answer any two questions. 2×4=8**

- State Newton’s law of cooling. Use it to find the specific heat capacity of a unknown liquid.
- Derive an expression for the pressure exerted by an ideal gas on the basis of Kinetic theory.
- Describe the working principle of diesel engine with the help of PV diagram.

** 7. Answer any one question. 4**

- Define lateral shift and derive an expression for it due to a parallel edged glass slab.
- Explain the construction and working of a compound microscope withfinal image at near point. Also, derive an expression for its magnifying power.

** 8. Answer any one question. 4**

- State and explain Gauss’s law in electrostatics and use it to determinethe electric field intensity due to a line charge.
- What is capacitance of a capacitor ? Derive a relation for the energystored in a capacitor when it is charged to a potential difference of V volts.

## Group ‘C’

** 9. Answer any three numerical questions. 3×4=12**

- A disoriented physics professor drives
*3.25 km*north, then*4.75 km*west and then*1.50 km*south. Find the magnitude and direction of the resultant displacement. - A bob of mass
*200 gram*is whirled in a horizontal circle of radius*50cm*by a string inclined at*30*^{ 0 }to the vertical. Calculate the tension in the string and the speed of the bob in the horizontal circle. - A copper wire and a steel wire of the same crosssectional area and of length
*1m*and*2 m*respectively are connected end to end. A force is applied, which stretches their combined length by*1cm*. Find how much each wire is elongated. - Eight spherical rain drops of the same mass and radius are falling down with a terminal speed
*5 cms*^{ -1 }. If they coalesce to form one big drop, what will be its terminal speed ?

** 10. Answer any two numerical questions. 2×4=8**

- A glass flask of volume
*400 cubic centimeter*is just filled with mercury at*0*. How much mercury will overflow when the temperature of the system rises to^{ 0 }C*80*.^{ 0 }C - A copper calorimeter of mass
*300 gm*contains*500gm*of water at temperature*15*. A^{0 }C*560 gm*block of aluminium at temperature*100*is dropped in the calorimeter and the temperature is observed to increase to^{ 0 }C*22.5*. Find the specific heat capacity of aluminium.^{ 0 }C - A certain volume of dry air at NTP is allowed to expand five times of its original volume under adiabatic condition. Calculate the final pressure and temperature.

** 11. A convex lens of focal length 24 cm and of refractive index 1.5 is totally immersed in water of refractive index 1.33.
Find its focal length in water. 4**

** 12. Three equal charges 1.8×10^{ -6 } C each are located at the corners of an equilateral triangle ABC of side 10 cm.
Calculate the electric potential due to these charges at the mid point of AB. 3**

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