# Class 11 Physics Pre-Board Examination-2020 [St. Xavier's College]

**Group A**

1. Answer in brief, any six questions: [6x2=12]

a. Write the dimensional formula of the capacitance and the universal gas constant.

b. Why spinning top can erect at its apex whereas rest top cannot easily be made erect at the aрех?

c. Plot the graph between variations of velocity with time in each of following cases:

a) when the acceleration has constant value

b) when the acceleration increases with time

d. What will happen if the capillary tube of insufficient height is dipped in water?

e. Why are the roads made winding in hilly region?

f. What would be the effect on maximum range in doubling the initial velocity of a projectile?

g. Why does heavy rifle not kick as strongly as a light rifle using same cartridges?

h. Under what condition will the sum of two vector of equal magnitude have magnitude equal to either vector?

2. **Answer in brief, any two questions: [2x2=4]**

a. A newspaper article about the weather states that “the temperature of body measures how much of heat the body contains". Is this description correct? Why or why not?

b. At very low pressure and high temperature, real gases behave like ideal gases. Why?

c. A person pours a cup of hot coffee, intended to drink it five minute later. To keep the coffee as hot as possible, should she cream in it or wait until just before she drink it? Explain

3. **Answer in brief, any one question: [1x2=2]**

a. Can we get pure spectrum without using convex lenses at both ends of a prism? Justify your answer.

b. Glass prism is immersed in water. What happens to the value of angle of minimum deviation?

4. **Answer in brief, any one question: [1x2=2]**

a. A proton is placed in a uniform electric field and then released. Then an electron is placed at this same point and released. Do these two particles experience the same acceleration? Do they move in the same direction when released?

b. A high voltage DC power line falls on a car, so the entire metal body of car is at a potential of 10000 V with respect to the ground. What happened to the occupants

a) when they are sitting on the car and

b) when they step out of the car?

Explain your reasoning.

**Group B**

5. **Answer any three questions: [3x4=12]**

a) What is elastic collision? Show that for an elastic collision in one dimension between the two bodies, moving in opposite direction, the relative velocity of approach is equal to the relative velocity of separation.

b) State and prove Bernoulli's principle.

c) Define simple harmonic motion. Deduce a relation for total energy of a simple harmonic motion.

d) Define centripetal and centrifugal forces. Derive an expression for the force acting on a body moving with uniform speed along a circular path.

6. **Answer any two questions: [2x4=8]**

a. Discuss the limitation of first law of thermodynamics. Also derive an expression for equation of ideal gas during adiabatic process relating its volume with pressure.

b. Define thermal conductivity. Describe Searle's experimental method to determine the thermal conductivity of a solid.

c. Define latent heat. Explain the method of determining the latent heat of vaporization by the method of mixture.

7. **Answer any one question: [1x4=4]**

a. Describe the construction and working of compound microscope producing final image at least distance of distinct division and hence derive an expression for its magnifying power.

b. Derive lens maker formula and State sign convention for the radius of curvature.

8. **Answer any one question: [1x4=4]**

a. What do you mean by potential gradient and electric field intensity? Deduce a relation between them.

b. Derive an expression for the energy stored in a capacitor of capacitance C when there is a potential difference V between the plates and also find expression of energy density.

**Group C**

9. **Solve any three of the following: [3x4=12]**

a. A composite wire of uniform diameter 2mm consisting of a copper wire of length 2.2 m and steel wire of 1.6m stretches under a load by 0.8mm. Calculate the load, given that the young's modulus of copper is 1.1x10^{11} N/m^{2} and for steel is 2x10^{11} N/m^{2}.

b. A boy can lift a maximum load of 250N of water. How many liters of mercury (Density 13600 kg/m^{3}) can he lift if contained in an identical vessel?

c. A dice which is released from rest on a plane inclines at 30° to the horizontal. The moment of inertia of disc about its center is 0.1kg m^{2} and its radius is 0.2 m. Find the angular velocity and its acceleration after it has rolled 2m down on the plane, given that its mass is 5kg.

d. A 200 kg satellite is lifted to an orbit of 2.2x10^{4} km radius. If the radius and mass of earth are 6.37x10^{6} m and 5.98x10^{24} kg respectively. How much additional energy is required to lift the satellite?

10. **Solve any two of the following: [2x4=8]**

a. What is the average translational kinetic energy of a molecule of an ideal gas at a temperature 27°C? What is the total random translational K.E. of the molecules in one mole of these gases? What is the rms speed of the oxygen molecules at this temperature?

b. A glass flask of volume 400cm^{3} is just filled with mercury at 0'°C. How much mercury overflows when the temperature of the system is raised to 80°C? Coefficient of cubical expansion of glass 1.2x10^{-5}/°C and that of mercury is 18x10^{-5}/°C

c. A Petrol engine consume 5kg of petrol per hour. If the power of engine is 20 KW and the calorific value of petrol is 11x10^{3} kCal per kg. Calculate the efficiency of the engine.

11. Light from a luminous point on the lower face of a rectangular glass slab, 2.0 cm thick, strikes the upper face and the totally reflected rays outline a circle of 3.2 cm radius on the lower face. What is the refractive index of the glass? **[4]**

12. A small sphere whose mass m is 1.0x10^{-3} gm. carries a charge q of 2.0x10^{-8} C. It hangs from a silk thread which makes an angle of 30° with a large charged conducting sheet. Calculate the surface charge density of the sheet. **[3]**

*******BEST OF LUCK*******

**Source: **Department of Physics, St. Xavier's College, Maitighar