Physics Question Paper
SECTION – A (10 × 2 = 20 Marks)
i) Answer all questions.
ii) Each question carries 2 marks.
iii) All are very short answer type questions.
- What is the discovery of C.V. Raman?
Answer: C.V. Raman discovered the Raman Effect in 1928, which is the scattering of light by molecules, leading to a change in the wavelength of the scattered light. This discovery earned him the Nobel Prize in Physics in 1930.
- What are significant figures and what do they represent when reporting the result of a measurement?
Answer: Significant figures are the digits in a number that carry meaningful information about its precision. They represent the certainty of a measurement and are important in conveying the accuracy of the reported data.
- A car travels the first third of a distance with a speed of 10 km/h, the second third at 20 km/h, and the last third at 60 km/h. What is its mean speed over the entire distance?
Answer: The mean speed is calculated by considering the total distance and total time taken. The formula for mean speed \( v_{mean} \) is:
\( v_{mean} = \frac{\text{Total distance}}{\text{Total time}} \). Since the distances for each section are the same, the mean speed turns out to be around 18 km/h. - According to Newton’s third law, every force is accompanied by an equal and opposite force. How can a movement ever take place?
Answer: Movement occurs because the forces act on different objects. For example, when a person walks, their foot pushes backward on the ground, and the ground exerts an equal and opposite force that moves the person forward.
- State the conditions under which a force does no work.
Answer: A force does no work if there is no displacement of the object in the direction of the force, or if the force is perpendicular to the direction of displacement.
- Why is it easier to balance a bicycle in motion?
Answer: When a bicycle is in motion, it has angular momentum, and the rotational inertia helps maintain its stability. The gyroscopic effect of the wheels also helps in balancing the bicycle.
- “Hydrogen is in abundance around the sun but not around earth”. Explain.
Answer: Hydrogen is abundant in the sun because of the high temperature and pressure, which allow hydrogen atoms to fuse and form helium in nuclear reactions. On Earth, hydrogen is rare due to its light nature and tendency to escape into space.
- What is the principle behind the carburetor of an automobile?
Answer: The carburetor works on the principle of Bernoulli’s principle. It mixes air and fuel in the right proportions, atomizing the fuel so it can be ignited in the engine, optimizing combustion and power output.
- What is greenhouse effect? Explain global warming.
Answer: The greenhouse effect occurs when certain gases, such as carbon dioxide, trap heat in the Earth’s atmosphere. This leads to an increase in the Earth’s temperature, a phenomenon known as global warming, which has been caused by human activities like deforestation and burning fossil fuels.
- Which of the two will increase the pressure more, an Adiabatic or an Isothermal process, in reducing the volume to 50%?
Answer: In an adiabatic process, the temperature rises more significantly than in an isothermal process when the volume is reduced, leading to a higher pressure. Thus, an adiabatic process increases pressure more than an isothermal process.
SECTION – B (6 × 4 = 24 Marks)
i) Answer any six of the following questions.
ii) Each question carries 4 marks.
iii) All are short answer type questions.
- State the parallelogram law of vectors. Derive an expression for the magnitude and direction of the resultant vector.
Answer: The parallelogram law of vectors states that if two vectors are represented by two adjacent sides of a parallelogram, their sum (resultant vector) is represented by the diagonal of the parallelogram. The magnitude \( R \) and direction of the resultant can be derived using the Pythagorean theorem and trigonometry:
\( R = \sqrt{A^2 + B^2 + 2AB\cos\theta} \) where \( A \) and \( B \) are the magnitudes of the two vectors, and \( \theta \) is the angle between them. - Explain the terms limiting friction, dynamic friction, and rolling friction.
Answer: – Limiting friction is the maximum frictional force that resists motion before an object starts moving. – Dynamic friction (or kinetic friction) occurs when an object is in motion and resists further movement. – Rolling friction is the frictional force that resists the motion of a rolling object, typically less than sliding friction.
- When 100 J of work is done on a flywheel, its angular velocity is increased from 60 rpm to 180 rpm. What is the moment of inertia of the wheel?
Answer: The work done on a rotating object is equal to the change in its rotational kinetic energy. Using the formula for rotational kinetic energy:
\( \Delta K.E. = \frac{1}{2} I (\omega_2^2 – \omega_1^2) \) where \( I \) is the moment of inertia, \( \omega_1 = 60 \, \text{rpm} \), \( \omega_2 = 180 \, \text{rpm} \), and the work done is 100 J. Solving for \( I \), we can find the moment of inertia. - What is escape velocity? Obtain an expression for it.
Answer: Escape velocity is the minimum speed an object must have to escape the gravitational influence of a planet or body. The formula for escape velocity \( v_e \) is:
\( v_e = \sqrt{\frac{2GM}{R}} \) where \( G \) is the gravitational constant, \( M \) is the mass of the body, and \( R \) is the radius of the body. - Describe the behavior of a wire under a gradually increasing load.
Answer: When a wire is subjected to a gradually increasing load, it first experiences elastic deformation, where it stretches without permanent change. After reaching the elastic limit, the wire enters the plastic deformation stage, where permanent elongation occurs. Eventually, if the load exceeds the breaking point, the wire will fracture.
- Explain hydraulic lift and hydraulic brakes.
Answer: Hydraulic lifts and brakes operate based on Pascal’s law, which states that pressure applied at any point in a confined fluid is transmitted undiminished throughout the fluid. A hydraulic lift uses fluid to amplify force for lifting heavy objects, while hydraulic brakes use fluid pressure to apply force to brake pads in a vehicle.
- Explain conduction, convection, and radiation with examples.
Answer: – Conduction is the transfer of heat through a solid due to the vibration of molecules (e.g., heating one end of a metal rod). – Convection is the transfer of heat through a fluid (liquid or gas) due to the movement of the fluid (e.g., boiling water). – Radiation is the transfer of heat through electromagnetic waves (e.g., sunlight warming the Earth).
- How specific heat capacity of monoatomic, diatomic, and polyatomic gases can be explained on the basis of Law of Equipartition of Energy?
Answer: According to the law of equipartition of energy, the energy is equally distributed among all degrees of freedom of the gas particles. Monoatomic gases have only translational degrees of freedom, diatomic gases have translational and rotational degrees, and polyatomic gases have translational, rotational, and vibrational degrees. The specific heat capacity increases with the number of degrees of freedom.
SECTION – C (2 × 8 = 16 Marks)
i) Answer any two of the following questions.
ii) Each question carries 8 marks.
iii) All are long answer type questions.
- State and prove Law of conservation of energy in case of a freely falling body. A pump is required to lift 60 kg of water per minute from a well 25m deep and to eject it with a speed of 50 m/s. Calculate the power required to perform the above task.
Answer: The Law of Conservation of Energy states that energy cannot be created or destroyed, but only transformed from one form to another. In the case of a freely falling body, the potential energy is converted into kinetic energy. The power required can be calculated as:
Power = Work/Time = \( \frac{mgh + \frac{1}{2}mv^2}{t} \) - Show that the motion of a simple pendulum is simple harmonic and hence derive an equation for its time period. What is the length of the seconds pendulum?
Answer: The motion of a simple pendulum is simple harmonic because the restoring force is proportional to the displacement. The time period \( T \) of the pendulum is derived as:
\( T = 2\pi \sqrt{\frac{L}{g}} \) The length of the seconds pendulum is 1 meter. - Explain reversible and irreversible processes. Describe the working of Carnot engine. Obtain an expression for the efficiency.
Answer: A reversible process is ideal and can be reversed without any energy loss, whereas an irreversible process results in energy dissipation. The Carnot engine operates between two reservoirs, and its efficiency is given by:
\( \eta = 1 – \frac{T_C}{T_H} \)