# JKBOSE Physics: Solved Previous Year’s Question Paper for NCERT/CBSE Class 12th Physics Paper Code (HSEIIRKON17–A)

## JKBOSE Physics: Solved Previous Year’s Question Paper for NCERT/CBSE Class 12th Physics Paper Code (HSEIIRKON17–A)

Question: What is meant by equipotential surface? Give two properties of the equipotential surface.

Answer: Equipotential surface is a surface in which all points on it have the same potential.

Two properties of equipotential surfaces are:

1. Equipotential surfaces are always perpendicular to electric field lines.

2. Equipotential surfaces never cross each other.

3. Establish the relation between the drift velocity of Electrons and electric current?

Question: How will you convert a galvanometer into Voltmeter?

Answer: To convert a galvanometer into a voltmeter, you will need to add a resistor in series with the galvanometer. The size of the resistor should be chosen such that the current through the galvanometer is limited to a safe value. Additionally, a switch should be added in parallel with the resistor. This switch should be used to bypass the resistor when a very small current needs to be measured. The galvanometer can then be used to measure the voltage across the resistor. The voltage measured will be proportional to the applied voltage.

Question: State and Explain Brewer’s law of Polarization.

Answer: Brewer’s law of Polarization states that when light passes through a transparent material, the intensity of the light that emerges from the material is proportional to the square of the refractive index of the material. This means that when light passes through a material with a higher refractive index (such as glass), more of the light is polarized and the intensity of the light that emerges is greater than the intensity of the light that entered the material. This is because the higher refractive index of the material causes the light to be bent more strongly, resulting in more of the light being polarized.

Question: Calculate the speed of light in a medium whose critical angle is 30 degrees.

Solution

Here, v=?, C=30∘
μ= cv= 1sinC
v= csin C=3×108×sin30∘=1.5×108m/s.

Question: Define the capacitance of a capacitor. Give its S.I.Unit.

Answer: Capacitance is a measure of a capacitor’s ability to store an electric charge. It is expressed as the ratio of the electric charge stored on each conductor to the voltage between them. The SI unit of capacitance is the farad (F), which is equal to one coulomb per volt (1 C/V).

Question: Define Modulation. What are the elements of a basic communication system?

Answer: Modulation is the process of altering the characteristics of a signal, such as amplitude, frequency, or phase, to transmit information.

The elements of a basic communication system include a transmitter, a channel or medium, a receiver, and an information source. The transmitter encodes the information into a signal, which is then transmitted through the channel or medium to the receiver. The receiver decodes the signal, and the information is recovered.

Question: Why does the sun look blue? Explain

Answer: Sunlight appears blue because of Rayleigh scattering, which is a type of scattering that occurs when light passes through a medium. When sunlight enters the Earth’s atmosphere, it interacts with molecules of nitrogen and oxygen, which scatter blue light more effectively than other colours. This causes the sky to appear blue, and the sun to appear even more blue because it is a much brighter source of light.

Question: Explain the term stopping potential and threshold frequency.

Answer: Stopping Potential: The stopping potential is the voltage which must be applied across the electrodes of a vacuum tube so that the electrons emitted by the cathode can just be prevented from reaching the anode. It is also known as the cutoff potential.

Threshold Frequency: Threshold frequency is the minimum frequency of light required to produce photoelectrons from a given material. When the frequency of light is below the threshold frequency, no photoelectrons will be emitted. The threshold frequency is determined by the work function of the material. The work function is the minimum energy required to remove an electron from the material.

Question: Explain Mass defect.

Answer: Mass defect is a phenomenon in nuclear physics which occurs when the mass of the nucleus of an atom is less than the sum of the masses of its constituent protons, neutrons and electrons. This occurs because a large amount of energy is released during the formation of a nucleus due to the strong nuclear force binding the particles together, and this energy is converted into mass according to the famous equation E=mc2. The difference between the mass of the nucleus and the sum of the masses of its constituent particles is known as the mass defect. The mass defect is responsible for the stability of nuclei, as it provides the energy needed to overcome the repulsive forces between the protons.

Question: Define the half-life and average life of a radioactive substance.

Answer: Half-life: The half-life of a radioactive substance is the amount of time it takes for half of the nucleus of an atom to decay.

Average life: The average life of a radioactive substance is the average amount of time it takes for a nucleus of an atom to decay. This is determined by the rate of decay of each atom and is usually much longer than the half-life.

Question: What are Dia, Para, and Ferromagnetic materials? Discuss their important properties.

Answer: Dia, Para, and Ferromagnetic materials are all types of magnetic materials.

Diamagnetic materials are materials that are weakly repelled by a magnetic field. They are not easily magnetized, but when placed in a magnetic field, they will form lines of magnetic force in opposition to the field. Examples of diamagnetic materials include water, graphite, and some metals like copper and aluminium.

Paramagnetic materials are materials that are weakly attracted by a magnetic field. They have a small, positive susceptibility to magnetism, which means they can be easily magnetized. Examples of paramagnetic materials include iron, cobalt, nickel, and some rare earth elements.

Ferromagnetic materials are materials that are strongly attracted by a magnetic field. They have a large, positive susceptibility to magnetism, which means they can be easily magnetized and remain magnetized even after the external magnetic field has been removed. Examples of ferromagnetic materials include iron, cobalt, and nickel.

The important properties of dia, para, and ferromagnetic materials include their ability to be magnetized, their ability to remain magnetized, and their ability to attract or repel other magnetic materials. Dia and para materials are generally used in applications that require a weak magnetic field, while ferromagnetic materials are generally used in applications that require a strong magnetic field.

Question: State Huygen’s principle and prove the laws of reflection on its basis.

Answer: Huygens’ Principle states that every point on a wavefront can be considered an independent source of wavelets that travel in all directions.

This principle can be used to prove the laws of reflection. When a wavefront of light strikes a boundary between two media, the wavefront is split into a reflected wave and a refracted wave. According to Huygens’ Principle, the wavefront can be treated as an infinite number of wavelets, each of which is reflected or refracted according to the law of reflection and refraction.

The law of reflection states that when a light wave strikes a boundary between two media, the angle of incidence (θi) is equal to the angle of reflection (θr). This can be seen in the diagram below.

Using Huygens’ Principle, we can see that each wavelet is reflected according to the law of reflection. The total reflected wave will be the sum of all the reflected wavelets, and because the angle of incidence is equal to the angle of reflection for each wavelet, the total reflected wave will also have an angle of incidence equal to the angle of reflection. Therefore, the law of reflection is proven based on Huygens’ Principle.

Objective Type Questions

Question: What is demodulation?

Answer: Demodulation is the process of extracting the original information-bearing signal from the modulated signal. It involves the removal of the carrier wave and the extraction of the original baseband signal. Demodulation can be used to recover analogue and digital signals.

Question: Define Isotones.

Answer: Isotones are atoms with the same number of neutrons but different numbers of protons. This means that they have the same mass number, but different atomic numbers.

Question: At what temperature would an intrinsic semiconductor behave like a perfect insulator?

Answer: At absolute zero temperature (0 K).

Question: The deviation through a glass prism is minimum when——–

Answer: The angle of incidence is equal to the angle of refraction.

Question: De—Broglie waves are associated with a moving particle irrespective of ———-

Question: Conductivity of semiconductor is————–

Answer: The conductivity of semiconductors is typically in the range of 10^-3 to 10^3 Siemens per meter (S/m). The conductivity of a semiconductor depends on the number of charge carriers available, which in turn is determined by the doping of the material.

Question: Lenz law is a consequence of the law of conservation of —–