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.
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 (γ ) = 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 Ε = 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 0 C. How much mercury will overflow when the temperature of the system rises to 80 0 C.
- A copper calorimeter of mass 300 gm contains 500gm of water at temperature 15 0 C. A 560 gm block of aluminium at temperature 100 0 C is dropped in the calorimeter and the temperature is observed to increase to 22.5 0 C . Find the specific heat capacity of aluminium.
- 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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