Maharashtra Board Physics 12th Exam 2024 : Most Important Question Answers for Last-Minute Revision

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Maharashtra Class 12 exams have started and you have very little time left for the Physics exam. Therefore, we are providing Most Important Answer Type Questions in this article. You can study them well and score well in your exams.

So this article is to help you ace those Most Important MCQs and Short Question answers with quick and effective last-minute revision.

MCQs (Multiple Choice Questions) are an important part of your Physics exam to score good marks. Mastering them can boost your confidence and lead to important scores.

These questions cover various topics from the Physics syllabus. Remember, it is important to understand the logic behind each answer to score well.

Maharashtra Board Physics Most Important Question Answers

Multiple Choice Questions

1. The emissive power of a body is

(a) the energy emitted by the body in a given time
(b) the radiant energy emitted by the body per unit area of the body
(c) the radiant energy emitted by the body per unit time
(d) the radiant energy emitted by the body per unit time per unit area of the body

Ans. (d) the radiant energy emitted by the body per unit time per unit area of the body

2. Two bodies have moments of inertia I₁ and I₂ and angular momentum L₁ and L₂ (L₁ < L₂). If they rotate with the same rotational kinetic energies, then

(a) I₂ < 1₁
(b) I₂ = I₁
(c) I₂ > I₁
(d) I₂ ≤ I₁

Ans. (c) I₂ > I₁

3. A fixed load resistance is connected to a Zener regulator. For an unregulated de input voltage Vin greater than the Zener voltage, the voltage across the current limiting series resistor is V_s. When Vin increases, the voltage across the load resistance is equal to

(a) V_s
(b) V_in - V_s
(c) V_in
(d) none of these

Ans. (b) V_in - V_s

4. In the vertical circular motion of a bob of mass m suspended by a string, the difference in the tensions in the string at a horizontal position and the uppermost position is

(a) mg
(b) 2mg
(c) 3mg
(d) 6mg

Ans. (c) 3mg

5. When seen from below, the blades of a ceiling fan are seen to be revolving anticlockwise and their speed is decreasing. Select the correct statement about the directions of its angular velocity and angular acceleration.

(a) Angular velocity upwards, angular acceleration downwards.
(b) Angular velocity downwards, angular acceleration upwards.
(c) Both angular velocity and angular acceleration upwards.
(d) Both angular velocity and angular acceleration downwards.

Ans. (b) Angular velocity downwards, angular acceleration upwards.

6. Raindrops are spherical in shape because of

(a) surface tension
(b) capillarity
(c) downward motion
(d) acceleration due to gravity

Ans. (a) surface tension

7. A liquid rises in a glass capillary tube to a height of 2.5 cm at room temperature. If another glass capillary tube of radius half that of the former is immersed in the same liquid, the rise of the liquid in it will be

(a) 1.25 cm
(b) 2.5 cm
(c) 5 cm
(d) 10 cm

Ans. (c) 5 cm

8. Colour of a shining bright star is an indication of its

(a) distance from the Earth
(b) size
(c) temperature
(d) mass.

Ans. (c) temperature

9. In an ideal gas, the molecules possess

(a) only kinetic energy
(b) both kinetic energy and potential energy
(c) only potential energy
(d) neither kinetic energy nor potential energy.

Ans. (a) only kinetic energy

10. If the pressure of an ideal gas is decreased by 10% isothermally, then its volume will

(a) decrease by 9%
(b) increase by 9%
(c) decrease by 10%
(d) increase by 11.11%.

Ans. (d) increase by 11.11%.

11. If a = 0.72 and r = 0.24, then the value of t is

(a) 0.02
(b) 0.04
(c) 0.4
(d) 0.2

Ans. (b) 0.04

12. The ratio of the emissive power of a perfectly blackbody at 1327 °C and 527 °C is

(a) 4 : 1
(b) 16 : 1
(c) 2 : 1
(d) 8 : 1

Ans. (b) 16 : 1

13. The second law of thermodynamics deals with transfer of

(a) work done
(b) energy
(c) momentum
(d) heat

Ans. (d) heat

14. During refrigeration cycle, heat is rejected by the refrigerant in the

(a) condenser
(c) evaporator
(b) cold chamber
(d) hot chamber

Ans. (a) condenser

15. Two identical springs of constant k are connected first in series and then in parallel. A block of mass m is suspended from the combination. The ratio of their frequencies for vertical oscillations will be in a ratio

(a) 1 : 4
(b) 1 : 2
(c) 2 : 1
(d) 4 : 1

Ans. (b) 1 : 2

16. When standing waves are produced on a string fixed at both ends,

(a) all particles vibrate in phase
(b) all antinodes vibrate in phase
(c) all alternate antinodes vibrate in phase
(d) all particles between two consecutive antinodes vibrate in phase

Ans. (d) all particles between two consecutive antinodes vibrate in phase

17. Which of the following phenomena proves that light is a transverse wave ?

(a) Reflection
(b) Interference
(c) Diffraction
(d) Polarization

Ans. (d) Polarization

18. The angle at which maximum torque is exerted by an uniform external electric field on an electric dipole is

(a) 0°
(b) 30°
(c) 45°
(d) 90º

Ans. (d) 90º

19. A parallel plate capacitor is charged and then isolated. On increasing the plate separation, the charge, potential and capacitance respectively

(a) remains constant, decreases, decreases
(b) increases, decreases, decreases
(c) remains constant, decreases, increases
(d) remains constant, increases, decreases

Ans. (a) remains constant, decreases, decreases

20. When the balance point is obtained in the potentiometer, a current is drawn from

(a) both the cell and auxiliary battery
(b) cell only
(c) neither cell nor auxiliary battery
(d) auxiliary battery only

Ans. (c) neither cell nor auxiliary battery

21. Soft iron is used to make the core of a transformer because of its

(a) low coercivity and low retentivity
(b) low coercivity and high retentivity
(c) high coercivity and high retentivity
(d) high coercivity and low retentivity

Ans. (a) low coercivity and low retentivity

22. A circular coil of 100 turns with a cross-sectional area of 1 m2 is kept with its plane perpendicular to the magnetic field of IT. The magnetic flux linked with the coil is

(a) 1 Wb
(b) 100 Wb
(c) 50 Wb
(d) 200 Wb

Ans. (b) 100 Wb

23. For a series LCR circuit, at resonance the impedance of the circuit is equal to

(a) the inductive reactance
(b) the capacitive reactance
(c) the resistance
(d) the inductive and capacitive reactance both

Ans. (c) the resistance

24. In a photoelectric cell, the product of the stopping potential and electronic charge is equal to

(a) the potential energy of the emitted electron
(b) the kinetic energy of the emitted electron
(c) the photoelectric work function of the emitter material
(d) the maximum kinetic energy that an emitted electron can have

Ans. (d) the maximum kinetic energy that an emitted electron can have

25. In a BJT, largest current flow occurs

(a) in the emitter
(b) in the collector
(c) in the base
(d) through the CB junction

Ans. (a) in the emitter

Very Short Answer Questions

Q1. Why is centrifugal force called a pseudo force ?

Ans. A force which arises from gravitational, electromagnetic or nuclear interaction between matter is called a real force. The centrifugal force does not arise due to any of these interactions. Therefore, it is not a real force.

The centrifugal force in the noninertial frame of reference of a particle in circular motion is the effect of the acceleration of the frame of reference with respect to an inertial frame of reference. Therefore, it is called a pseudo or fictitious force.

Q2. What happens when a ballet dancer stretches her arms while taking turns ?

Ans. When a ballet dancer stretches her arms in a dance spin, her moment of inertia increases. Consequently her angular speed decreases to conserve angular momentum. This reduces the linear speed of an ice ballet dancer to prevent skidding while taking turns of larger radius.

Q3. State any two applications of Pascal's law.

Ans. Applications of Pascal's law :

(1) Hydraulic car lift and hydraulic press

(2) Hydraulic brakes

Q4. Why is cold wash recommended for new cotton fabrics while hot wash for removing stains ?

Ans. Cold wash is recommended for new/coloured cotton fabrics. Cold water, due to its higher surface tension, does not penetrate deep into the fibres and thus does not fade the colours. Hot water, because of its lower surface tension, can penetrate deep into fabric fibres and remove tough stains.

Q5. What is the effect on the surface tension of (i) molten copper (ii) molten cadmium on increasing its temperature ?

Ans. The surface tension of (i) molten copper (ii) molten cadmium increases on increasing its temperature.

Q6. What is meant by a steady flow ?

Ans. When a liquid flows slowly over a surface or through a pipe such that its velocity or pressure at any point within the fluid is constant, it is said to be in steady flow.

Q7. What is viscous drag ?

Ans. When a fluid flows past a solid surface, or when a solid body moves through a fluid, there is always a force of fluid friction opposing the motion. This force of fluid friction is called the drag force or viscous drag.

Q8. What is thermal equilibrium ?

Ans. A system is in a state of thermal equilibrium if there is no net transfer of heat between the various parts of the system or between the system and its surroundings, so that the temperature remains constant and uniform throughout the system.

Q9. What is an isothermal process ?

Ans. A process in which changes in pressure and volume of a system take place at a constant temperature is called an isothermal process.

Q10. In which thermodynamic process does the total internal energy of a system remain constant ?

Ans. The total internal energy of a system remains constant in an isothermal process.

Q11. Give an example of some familiar process in which no heat is added to or removed from a system, but the temperature of the system changes.

Ans. A free expansion is an adiabatic process in which the temperature of the gas changes although no heat is added to or removed from the system (gas).

Q12. A tuning fork is in resonance with a closed pipe. But the same tuning fork cannot be in resonance with an open pipe of the same length. Why ?

Ans. For the same length of air column, and the same speed of sound, the fundamental frequency of the air column in a closed pipe is half that in an open pipe. Hence, a tuning fork in unison with the air column in a closed pipe cannot be in unison with the air column of the same length in an open pipe.

Q13. How is Young's interference experiment performed using a single source of light ?

Ans. When a narrow slit is placed in front of an intense source of monochromatic light, cylindrical wavefronts propagate from the slit. In Young's experiment, two coherent sources are then obtained by wavefront splitting by placing a second screen with two narrow slits at a small distance from the first slit.

Q14. Give a common use of a polarizer.

Ans. Polaroid sunglasses and filter for camera lens are used to reduce or eliminate intense reflected light from reflective nonmetallic surfaces like glass, rock faces, roadways and water.

Q15. What is Fresnel diffraction ?

Ans. In Fresnel diffraction, either the source of light or the screen or both are at finite distances from the diffracting aperture.

Q16. What is the shape of equipotential surfaces in a uniform electric field ?

Ans. In a uniform electric field, the field lines are equally-spaced parallel lines and the equipotential surfaces are parallel planes perpendicular to the field lines. For equal potential differences between adjacent planes, these equipotentials are equally spaced.

Q17. What is the resistance of an ideal voltmeter ?

Ans. Infinite.

Q18. What is a potentiometer ?

Ans. A potentiometer is an instrument for measuring, comparing or dividing small potential differences. It consists of a long and uniform resistance wire along which a potential gradient is set up by connecting a cell of extremely stable emf connected across its ends.

Q19. What will be the effect on the position of null point on a potentiometer wire if the current through the wire is decreased ?

Ans. The potential gradient along a potentiometer wire is directly proportional to the current through the wire and the null length on potentiometer is inversely proportional to the potential gradient. Hence, the potential gradient decreases with a decrease in the current. Consequently, the null length will decrease.

Q20. What happens when a rod of diamagnetic material is placed in a nonuniform magnetic field ?

Ans. When a rod of a diamagnetic material is placed in a nonuniform
magnetic field, it is repelled from the region of strong field.

Q21. What happens when a rod of diamagnetic material is suspended in a uniform magnetic field ?

Ans. When a thin rod of a diamagnetic material is suspended in a uniform
magnetic field, it comes to rest with its length perpendicular to the field.

Q22. What happens to a ferromagnetic material when it is heated above its Curie temperature ?

Ans. When a ferromagnetic material is heated above its Curie temperature, spontaneous domain magnetization is lost due to increased thermal agitation. Without the domain structure, the atomic magnetic moments are randomly oriented so that the material undergoes an order to disorder phase transition to a paramagnetic material.

Q23. Which property of soft iron makes it useful for making an electromagnet ?

Ans. An electromagnet should become magnetic when a current is passed through its coil but should lose its magnetism once the current is switched off. Hence, the ferromagnetic core (usually iron-based) used for an electromagnet should have high permeability and low retentivity, i.e., it
should be magnetically 'soft'.

Q24. What is magnetic shielding ?

Ans. The use of a shell or box of magnetic material of high permeability to protect sensitive instruments from stray magnetic fields is called magnetic shielding.

Q25. Why is the base of a transistor made thin and is lightly doped ?

Ans. The base of a transistor is lightly doped than the emitter and is made narrow so that virtually all the electrons injected from the emitter (in an npn transistor) diffuse right across the base to the collector junction without recombining with holes. That is, the base width is kept less than the recombination distance. Also, the emitter is much heavily doped than the base to improve emitter efficiency and common-base current gain x.

Defination

1. Uniform circular motion.

Ans. A particle is said to perform uniform circular motion if it moves in a circle or a circular arc at constant linear speed or constant angular velocity.

2. Centripetal force.

Ans. In the uniform circular motion of a particle, the centripetal force is the force on the particle which at every instant points radially inward and produces the centripetal acceleration necessary to make the particle move in its circular path.

3. Coefficient of viscosity.

Ans. The coefficient of viscosity of a fluid is defined as the viscous drag per unit area acting on a fluid layer per unit velocity gradient established in a steady flow.

4. Angle of contact.

Ans. The angle of contact for a liquid-solid pair (a liquid in contact with a solid) is defined as the angle between the surface of the solid and the tangent drawn to the free surface of the liquid at the extreme edge of the liquid, as measured through the liquid.

5. Coefficient of absorption (Absorptance).

Ans. The coefficient of absorption (absorptance or absorptive power) of a body is defined as the ratio of the quantity of radiant energy absorbed by the body to the quantity of radiant energy incident on the body in the same time.

6. Coefficient of reflection (Reflectance).

Ans. The coefficient of reflection (reflectance) of the surface of a body is defined as the ratio of the quantity of radiant energy reflected by the surface to the quantity of radiant energy incident on the surface in the same time.

7. Coefficient of transmission (Transmittance).

Ans. The coefficient of transmission (transmittance) of a body is defined as the ratio of the quantity of radiant energy transmitted by the body to the quantity of radiant energy incident on the body in the same time.

8. Ideal simple pendulum.

Ans. An ideal simple pendulum is a heavy point mass suspended from a rigid support by a weightless, inextensible and twistless string, and set oscillating under gravity through a small angle in a vertical plane.

9. Seconds pendulum.

Ans. A simple pendulum of period two seconds is called a seconds pendulum.

10. Angular SHM.

Ans. Angular SHM is defined as the oscillatory motion of a body in which the restoring torque responsible for angular acceleration is directly proportional to the angular displacement and its direction is opposite to that of angular displacement.

11. Progressive wave OR Travelling wave.

Ans. A progressive wave or a wave motion is a periodic or oscillatory disturbance in a medium or in vacuum which is propagated without any damping and obstruction from one place to another at a finite speed.

12. Transverse progressive wave.

Ans. A progressive wave in which the vibration of the individual particles of the medium is perpendicular to the direction of propagation of the wave is called a transverse progressive wave.

13. Longitudinal progressive wave.

Ans. A progressive wave in which the vibration of the individual particles of the medium is along the line of propagation of the wave is called a longitudinal progressive wave.

14. Stationary wave or Standing wave.

Ans. When two identical progressive waves, i.e., waves having the same amplitude, wavelength and speed, propagate in opposite directions through the same region of a medium, their superposition under certain conditions creates a stationary interference pattern called a stationary wave or a standing wave.

15. Electric potential difference.

Ans. The electric potential difference between two points in an electric field is defined as the work done per unit charge by an external agent against the electric force in moving an infinitesimal positive charge from one point to the other without acceleration.

16. Electric potential.

Ans. The electric potential at a point in an electric field is defined as the work per unit charge that must be done by an external agent against the electric force to move without acceleration a sufficiently small positive test charge from infinity to the point of interest.

17. Magnetization.

Ans. The magnetization of the material is defined as the net magnetic moment per unit volume of a material.

18. Magnetic intensity.

Ans. The magnetic intensity is defined as the magnetic induction in an isotropic medium divided by the permeability of the medium.

19. Threshold frequency.

Ans. The threshold frequency for a given metal surface is defined as the characteristic minimum frequency of the incident radiation below which no photoelectrons are emitted from that metal surface.

20. Threshold wavelength.

Ans. The threshold wavelength for a given metal surface is defined as the characteristic maximum wavelength of the incident radiation above which no photoelectrons are emitted from that metal surface.

21. Mean-life of a radioactive element.

Ans. The mean-life of a radioactive element is the average time for which the undecayed nuclei of the element exist before decaying. It is equalto the reciprocal of the decay constant of that element.

22. Nuclear fission.

Ans. Nuclear fission is a nuclear reaction in which a heavy nucleus of an atom splits into two or more fragments of comparable size either spontaneously or when bombarded by a neutron, with the release of enormous amount of energy.

23. Nuclear fusion.

Ans. Nuclear fusion is a type of nuclear reaction in which lighter atomic nuclei (of low atomic numbers) fuse to form a heavier nucleus (of higher atomic number) with the release of enormous amount of energy.

24. Barrier potential.

Ans. The barrier potential is defined as the electric potential difference across the depletion region of a pn-junction.

25. Rectification.

Ans. The process of converting an alternating voltage (or current) to a direct voltage (or current) is called rectification.

Laws & Theory

Q1. State Pascal's law.

Ans. Pascal's law : A change in the pressure applied to an enclosed fluid at rest is transmitted undiminished to every point of the fluid and to the walls of the container, provided the effect of gravity can be ignored.

Q2. State Bernoulli's principle.

Ans. Bernoulli's principle : Where the velocity of an ideal fluid in streamline flow is high, the pressure is low, and where the velocity of a fluid is low, the pressure is high.

Q3. State Faraday's laws of electromagnetic induction.

Ans. Faraday's laws of electromagnetic induction :

First law : Whenever there is a change in the magnetic flux associated with a circuit, an emf is induced in the circuit.

Second law : The magnitude of the induced emf is directly proportional to the time rate of change of magnetic flux through the circuit.

Q4. State the causes of induced current and explain them on the basis of Lenz's law.

Ans. According to Lenz's law, the direction of the induced emf or current is such as to oppose the change that produces it. The change that induces a current may be

(i) the motion of a conductor in a magnetic field or

(ii) the change of the magnetic flux through a stationary circuit

In the first case, the direction of induced emf in the moving conductor is such that the direction of the side-thrust exerted on the conductor by the magnetic field is opposite in direction to its motion. The motion of the conductor is, therefore, opposed.

In the second case, the induced current sets up a magnetic field of its own which within the area bounded by the circuit is (a) opposite to the original magnetic field if this field is increasing, but (b) is in the same direction as the original field, if the field is decreasing. Thus, it is the change in magnetic flux through the circuit (not the flux itself) which is opposed by the induced current.

Q5. State Stokes' law.

Ans. Stokes' law : If a fluid flows past a sphere or a sphere moves through a fluid, for small enough relative speed v₀ for which the flow is streamline, the viscous force on the sphere is directly proportional to the coefficient of viscosity of the fluid n, the radius r of the sphere and the free-stream velocity V_0.

Q6. State the zeroth law of thermodynamics.

Ans. Zeroth law of thermodynamics: If two systems are each in thermal equilibrium with a third system, they are also in thermal equilibrium with each other.

Q7. State the first law of thermodynamics.

Ans. First law of thermodynamics: The change in the internal energy of a system (ΔU) is the difference between the heat supplied to the system (0) and the work done by the system on its surroundings (W). Mathematically, ΔU = Q - W, where all quantities are expressed in the same units.

Q8. State the two forms of the second law of thermodynamics.

Ans. Second law of thermodynamics :

(1) Kelvin-Planck statement : It is impossible to extract an amount of heat QH from a hot reservoir and use it all to do work W. Some amount of heat Qc must be exhausted (given out) to a cold reservoir. This prohibits the possibility of a perfect heat engine. This statement is also called the first form or the engine law or the engine statement of the second law of thermodynamics.

(2) Clausius statement : It is not possible for heat to flow from a colder body to a warmer body without any work having been done to accomplish this, i.e., there is no perfect refrigerator. This statement is called the second form of the second law of thermodynamics.

Q9. State Huygens' principle.

Ans. Huygens' principle : Every point on a wavefront acts as a secondary source of light and sends out secondary wavelets in all directions. The secondary wavelets travel with the speed of light in the medium and are effective only in the forward direction. At any instant, the forward-going envelope or the surface of tangency to these wavelets gives the position of the new wavefront at that instant.

Q10. State the merits and demerits of Huygens' theory.

Ans. Merits of Huygens' theory :

(1) Huygens' wave theory satisfactorily explains reflection and refraction as well as their simultaneity.

(2) In explaining refraction, the theory concludes that the speed of light in a denser medium is less than that in a rarer medium, which agreed with later experimental findings.

(3) The theory was later used by Young (1800-04), Fraunhofer and Fresnel (1814) to satisfactorily explain interference, diffraction and rectilinear propagation of light. The phenomenon of polarization could also be explained by considering the light waves to be transverse.

Demerits of the theory :

(1) It was found much later that the hypothetical medium, lumini-ferous ether, has no experimental basis. In 1905, Einstein discarded the idea of ether completely.

(2) Phenomena like absorption and emission of light by atoms and molecules, photoelectric effect, Raman effect, Compton effect, etc., cannot be explained on the basis of the wave theory.

Short Answer Questions

Q1. Do we need a banked road for a two-wheeler ? Explain.

Ans. When a two-wheeler takes a turn along an unbanked road, the force of friction is the centripetal force. The two-wheeler leans inward to counteract a torque that tends to topple it outward. But, friction cannot be relied upon to provide the necessary centripetal force on all road conditions. Secondly, the friction results in wear and tear of the tyres. On a banked road at a turn, any vehicle can negotiate the turn without depending on friction and without straining the tyres.

Q2. In a vertical circular motion, is zero speed possible at the top (uppermost point)? Under what condition(s) ?

Ans. In a nonuniform vertical circular motion, e.g., that of a small body attached to a string or the loop-the-loop manoeuvres of an aircraft or motorcycle, the body must have some minimum speed to reach the top and complete the circle. In this case, the motion is controlled only by gravity and zero speed at the top is not possible.

However, in a controlled vertical circular motion, e.g., that of a small body attached to a rod or of a giant wheel (Ferris wheel) ride, the body or the passenger seat can have zero speed at the top, i.e., the motion can be brought to a stop.

Q3. Explain the effect of impurity on the angle of contact (or surface tension of a liquid).

Ans. Effect of impurity :

(1) The angle of contact or the surface tension of a liquid increases with dissolved impurities like common salt. For dissolved impurities, the angle of contact (or surface tension) increases linearly with the concentration of the dissolved materials.

(ii) It decreases with sparingly soluble substances like phenol or alcohol. A detergent is a surfactant whose molecules have hydrophobic and bydrophilic ends; the hydrophobic ends decrease the surface tension of water. With reduced surface tension, the water can penetrate deep into the fibres of a cloth and remove stubborn stains.

(iii) It decreases with insoluble surface impurities like oil, grease or dust. For example, mercury surface contaminated with dust does not form perfect spherical droplets till the dust is removed.

Q4. What do you mean by viscous drag ? What causes viscous drag in fluids ?

Ans. When a fluid flows past a solid surface, or when a solid body moves through a fluid, there is always a force of fluid friction opposing the motion. This force of fluid friction is called the drag force or viscous drag. In liquids, the viscous drag is due to short range molecular cohesive forces while in gases it is due to collisions between fast moving molecules. For laminar flow in both liquids and gases, the viscous drag is proportional to the relative velocity between the layers, provided the relative velocity is small. For turbulent flow, the viscous drag increases rapidly and is proportional to some higher power of the relative velocity.

Q5. What are the limitations of the first law of thermodynamics ?

Ans. Limitations of the first law of thermodynamics : There can be thermodynamic processes which are consistent with the first law but not observed in nature.

(1) According to first law of thermodynamics, heat and work are interconvertible. But, the law does not tell us whether a particular process can or cannot occur. For example, we see a net transfer of energy (heat) from a hot body to a cold body but never the other way.

(2) The law does not rule out total (i.e., 100%) conversion of heat into work or work into heat. However, this never occurs in practice. It is impossible to design a heat engine that can completely convert heat into work, i.e., no heat engine is 100% efficient. Similarly, it is impossible to remove heat from a system without doing some work on the system, i.c., the coefficient of performance of a refrigerator can never be infinite.

(3) Diffusion of two dissimilar inert gases is an irreversible process. For example, we never see the reverse process of a gaseous mixture separating into separate chambers, although such a process would not violate the first law.

Q6. A solar cooker and a pressure cooker both are used to cook food. Treating them as thermodynamic systems, discuss the similarities and differences between them.

Ans. Solar cooker and pressure cooker treated as thermodynamic systems :

Similarities :

(1) Heat must be added to both the systems.

(2) Internal energy (temperature) of the systems increases.

Differences :

(1) A solar cooker is an open thermodynamic system while a pressure cooker is a closed system.

(2) The contents of a solar cooker are at normal or surrounding pressure and the food is cooked at the normal boiling point of water. In the case of a pressure cooker, the increase in pressure increases the boiling point of water thereby cooking the food faster.

Q7. Explain any two applications of beats.

Ans. Applications of beats :

(1) Listening for beats - or rather, their absence is the usual method of tuning musical instruments and in the determination of the frequency of a musical note.

(2) Ultrasonic calls of bats and dolphins may be detected by superimposing a sound of different frequency to produce audible beats.

(3) In music, beats are used to produce a low frequency sound (a grave tone). Two notes whose difference in frequency is equal to the desired low frequency are used for this purpose. When two notes are nearly in tune, the beats are slow. But as the beat frequency increases to 20 Hz or more, the beats may ultimately merge into a continuous tone known as a difference tone.

(4) (i) Speed of a moving object can be determined using a Doppler RADAR. Radio waves from the RADAR are reflected off a moving object, such as an aeroplane. The superposition of the incident and reflected waves produces beats. The frequency of beats helps to determine the speed of the aeroplane.

The same principle is used in speed guns used by traffic police to determine the speed of cars on a highway.

(ii) In medicine, a Doppler ultrasound test (sonography) uses reflected sound waves to evaluate blood flow through the major arteries and veins of the arms, legs and neck. It can show blocked or reduced blood flow because of narrowing of the major arteries. Duplex (or 2D) Doppler, Colour Doppler and Power Doppler are different techniques of the same test.

Q8. State the properties of conductors in electrostatic conditions.

Ans. Properties of a charged conductor in electrostatic conditions :

(1) Net electric field inside the conductor is zero.

(2) Net electric field just outside the conductor is normal to its surface at every point.

(3) Electric potential inside the conductor is constant and equal to that on its surface.

(4) Excess charges reside only on the surface of the conductor but, for a conductor of arbitrary shape, the surface charge density at a point is inversely proportional to the local curvature of the surface.

Q9. What is electrostatic shielding ? What is a Faraday cage ?

Ans. The use of a conducting box to protect sensitive instruments from stray electric fields, or the use of a conducting wire cage to protect a person near a high-voltage installation or from lightning strike, is called electrostatic shielding.

The hollow conductor or the conducting wire cage that shields its interior from external electric fields is called a Faraday cage or Faraday shield.

Q10. What are the disadvantages of a potentiometer (over a voltmeter) ?

Ans. Disadvantages of a potentiometer over a voltmeter :

(1) The use of a potentiometer is an indirect measurement method while a voltmeter is a direct reading instrument.

(2) A potentiometer is unwieldy while a voltmeter is portable.

(3) Unlike a voltmeter, the use of a potentiometer in measuring an unknown emf requires a standard source of emf and calibration.

Q11. State the function of the shunt in modifying a galvanometer to an ammeter.

Ans. Functions of the shunt in an ammeter :

(1) It lowers the effective resistance of the ammeter.

(2) It shunts off a larger fraction of the line current, thus protecting the sensitive meter movement of the basic galvanometer.

(3) With a shunt of proper value, a galvanometer can be modified into an ammeter of practically any desired range.

Q12. State the functions of the series resistance in modifying a galvanometer into a voltmeter.

Ans. Functions of the high series resistance in a voltmeter :

(1) It increases the effective resistance of the voltmeter.

(2) It drops off a larger fraction of the measured potential difference, thus protecting the sensitive meter movement of the basic galvanometer.

(3) With a resistance of proper value, a galvanometer can be modified to a voltmeter of any desired range.

Q13. What is a diamagnetic material? Give two examples.

Ans. A material which is weakly repelled by a magnet and whose atoms/molecules do not possess a net magnetic moment in the absence of an external magnetic field is called a diamagnetic material. A diamagnetic material placed in a uniform magnetic field acquires a small net induced magnetic moment directed opposite to the field.

Examples: Bismuth, copper, gold, silver, antimony, mercury, water, air, hydrogen, lead, silicon, nitrogen, sodium chloride.

Q14. What is a paramagnetic material? Give two examples.

Ans. A material which is weakly attracted by a magnet and whose atoms possess a net magnetic moment with all atomic magnetic moments randomly directed in the absence of an external magnetic field but are capable of being aligned in the direction of the applied magnetic field is called a paramagnetic material.

Examples: Aluminium, platinum, chromium, manganese, sodium, calcium, magnesium, lithium, tungsten, niobium, copper chloride, oxygen.

Q15. If a copper disc swings between the poles of a magnet, the pendulum comes to rest very quickly. Explain the reason. What happens to the mechanical energy of the pendulum ?

Ans. As the copper disc enters and leaves the magnetic field, the changing magnetic flux through it induces eddy current in the disc. In both cases, Fleming's right hand rule shows that opposing magnetic force damps the motion. After a few swings, the mechanical energy becomes zero and the motion comes to a stop. Joule heating due to the eddy current warms up the disc. Thus, the mechanical energy of the pendulum is transformed into thermal energy.

Q16. State any two limitations of Bohr's atomic model.

Ans. Bohr's atomic model cannot explain

(1) the relative intensities of spectral lines even in the hydrogen spectrum

(2) the atomic spectra of many-electron atoms of higher elements

(3) the Zeeman effect and Stark effect, and associated molecular bonding

Q17. Why do we need filters in a power supply ?

Ans. A rectifier-half-wave or full-wave-outputs a pulsating de which is not directly usable in most electronic circuits. These circuits require nearly pure de as produced by batteries. Unlike pure de waveform of a battery, a rectifier output has an ac ripple riding on a de waveform. The circuit used in a de power supply to remove the ripple is called a filter. A filter circuit can produce smoother waveform that approximates the waveform produced by a battery. The most common technique used for filtering is a capacitor connected across the output of a rectifier.

Q18. State any four advantages of a photodiode.

Ans. Advantages of a photodiode :

(1) Quick response to light and hence high operational speed.

(2) Excellent linear response over a wide dynamic range.

(3) Low cost.

(4) Wide spectral response.

(5) Compact, lightweight, mechanically rugged and long life.

Q19. State the principle and any two uses of a solar cell.

Ans. Principle: A solar cell works on the photovoltaic effect in which an emf is produced between the two layers of a pn-junction as a result of irradiation.

Uses of solar cells :

(1) A solar cell array consisting of a set of solar cells is used during daylight hours to power an electrical equipment as well as to recharge batteries which can then be used during night.

(2) Solar cell arrays are used to power electrical equipment on a satellite as well as at remote places on the Earth where electric power lines are absent.

(3) Large-scale solar power generation systems linked with commercial power grid.

(4) Independent power supply systems for radar detectors, monitoring systems, radio relay stations, roadlights and roadsigns.

Q20. State any two advantages of a full-wave rectifier.

Ans.

(1) A full-wave rectifier rectifies both halves of each cycle of the ac input.

(2) Efficiency of a full-wave rectifier is twice that of a half-wave rectifier.

(3) The ripple in a full-wave rectifier is less than that in a half-wave rectifier.

Q21. What is the advantage of a radial magnetic field in a moving-coil galvanometer and how is it produced ?

Ans.

(1) Advantage of radial magnetic field in a moving-coil galvanometer :

(i) As the coil rotates, its plane is always parallel to the field. That way, the deflecting torque is always a maximum depending only on the current in the coil, but not on the position of the coil.

(ii) The restoring torque is proportional to the deflection so that a radial field makes the deflection proportional to the current. The instrument then has a linear scale, i.e., the divisions of the scale are evenly spaced. This makes it particularly straight forward to calibrate and to read.

(2) Producing radial magnetic field :

(i) The pole pieces of the permanent magnet are made cylindrically concave, concentric with the rotation axis of the coil.

(ii) A soft iron cylinder is centred between the pole pieces so that it forms a narrow cylindrical gap in which the sides of the coil can move. Together, they produce a radial magnetic field; that is, the magnetic lines of force in the gap are along radii to the central axis.

Q22. What do you mean by a polar molecule and a nonpolar molecule ? Give one example of each.

Ans. A polar molecule is one with a permanent electric dipole moment that arises from the finite separation of the centres of the net positive charge and the net negative charge in the molecule, even in the absence of an external electric field.

Examples : Gaseous hydrogen halides (HF, HCl, etc.); NH₃, NO₂, N₂O₃, water molecules; all heteronuclear diatomic molecules (with any covalent bond between two different atoms).

A nonpolar molecule is one which does not have a permanent electric dipole moment because in the absence of an external electric field, the centres of the net positive charge and the net negative charge in the molecule coincide.

Examples: H₂, CO₂, N₂, polyethylene, polystyrene.

Q23. What is end correction? State the cause of end correction. How is it estimated?

Ans. When sound waves are sent down the air column in a narrow closed or open pipe, they are reflected at the ends without phase reversal at an open end and with a phase reversal at a closed end. Interference between the incident and reflected waves under appropriate conditions sets up stationary waves in the air column. Thus, the stationary waves have an antinode at an open end.

However, because air molecules in the plane of an open end are not free to move in all directions, reflection of the longitudinal waves takes place slightly beyond the rim of the pipe at an open end. The distance of the antinode from the open end of the pipe is called end correction. According to Reynolds, the distance of the antinode from the rim is approximately 30% of the inner diameter of a cylindrical pipe. This distance must be taken into account in accurate determination of the wavelength of sound. Hence, this distance is called the end correction.

Therefore, if d is the inner diameter of a cylindrical pipe, an end correction e=0.3d for each open end must be added to the measured length of the pipe. If / is the measured length, the effective length of the air column in the case of a pipe closed at one end is / +0.3d, while that for a pipe open at both ends is / +0.6d.

Q24. Define a reversible process. What is an irreversible process ?

Ans. A reversible process is one which is performed in such a way that, at the end of the process, both the system and its local surroundings can be restored to their initial states, without producing any change in the rest of the universe. A process may be reversible if it takes place quasistatically and without dissipative effects.

A process which does not fulfill the requirements of reversibility is said to be an irreversible process. In this case, the system and the local surroundings cannot be restored to their initial states without affecting the rest of the universe. All natural processes are irreversible.

Q25. State the applications of Bernoulli's principle.

Ans. Applications of Bernoulli's principle :

(1) Venturi meter : It is a horizontal constricted tube that is used to measure flow speed in a gas.

(2) Atomizer : It is a hydraulic device used for spraying insecticide, paint, air perfume, etc.

(3) Aerofoil : The aerofoil shape of the wings of an aircraft produces aerodynamic lift.

(4) Bunsen's burner : Bernoulli effect is used to admit air into the burner to produce an oxidising flame.

Maharashtra Board HSC (Class 12) 2024 Biology : Practice Paper with Solution; Download PDF

Maharashtra Board HSC (Class 12) 2024 Physics : Practice Paper with Solution; Download PDF

Maharashtra Board HSC (Class 12) 2024 Mathematics : Practice Paper with Solution; Download PDF