## JKBOSE Physics: Solved Previous Year’s Question Paper for NCERT/CBSE Class 12th Physics Paper Code (6416——X)

** Short Answer Type Questions**

**Question: State and explain Ampere circuit law**

Answer: Ampere’s Circuit Law is a fundamental law that states that the total magnetic field around a closed path is equal to the current passing through the path multiplied by the constant of proportionality, the permeability of free space μ0.

Mathematically, this can be expressed as B⋅dl=μ0I, where B is the magnetic field, dl is the differential line element, and I is the current. The magnetic field at a point inside a solenoid carrying current can be calculated using Ampere’s Law: B = μ0NI/L, where N is the number of turns of the solenoid, I is current, and L is the length of the solenoid.

**Question: What is meant by Root mean square value of alternating current?**

Answer: The Root mean square (RMS) value of an alternating current (AC) is a measure of its effective value, which is equal to the square root of the mean of the squares of its instantaneous values. It is a measure of the power of an AC signal and is used to compare the magnitude of different AC signals.

**Question: A wire of resistance one ohm is stretched to double its length. What is the new resistance?**

Solution:

Here,

R=1Ω,Length=L,Cross-sectional area, CSA=A

The formula used is,

R=ρAL⟹ρAL=1……….(i)

The new length, L′=2L

And new CSA = A′

So we have,

The volume of the wire= AL

Now after the act of stretching the volume remains constant.

Therefore, AL=A′L′

⟹AL=2LA′⟹A′=2A

Now the new resistance of the wire becomes

Rnew=ρA′L′⟹Rnew=ρ2A2L⟹Rnew=4ρAL

Rnew=4×1 by using equation (i)

Therefore the new resistance is 4Ω

**Question: Define the resistivity of the material and discuss the factors on which it depends.**

Answer: Resistivity is a measure of a material’s opposition to the flow of electric current. It is symbolized by the Greek letter ρ (rho) and measured in units of ohm-meters (Ω-m). Resistivity depends on a material’s composition and structure. For example, metals typically have higher resistivities than nonmetals.

The resistivity of a particular material depends on several factors, including

The type of material, the temperature of the material, the amount of impurities in the material, and the amount of pressure applied to the material.

Materials with higher temperatures tend to have higher resistivities, as the increased temperature causes more collisions between particles, thus slowing the flow of current. The presence of impurities in a material can also increase its resistivity. Finally, increased pressure on a material can decrease its resistivity, as the increased pressure reduces the amount of available space for current-carrying particles to move around.

**Question: State and prove Brewester’s law**

Answer: Brewster’s law states that the reflected light rays from a medium such as glass or water will be completely polarized at a specific angle of incidence. This angle is known as the Brewster angle and is related to the refractive index of the medium. Mathematically, Brewster’s law can be expressed as:

n sin θ B = sin θ i

Where n is the refractive index of the medium, θB is the Brewster angle, and θi is the angle of incidence.

This law can be proven using the Fresnel equations. The Fresnel equations describe the reflection and refraction of light when it passes from one medium to another. By applying the Fresnel equations to the Brewster angle, it can be shown that the reflected light will be completely polarized.

**Question: Calculate the radius of the smallest orbit of the Hydrogen atom.**

Solution

The radius of the nth orbit of a hydrogen atom is given by

rn=ε0h2n/πme2

For the smallest orbit, n=1

⇒r0=h2(4πε0)4π2me2

=(6.6×10−34)24π2×9.1×10−31×9×109×(1.6×10−19)3m

=0.53 Å

This is known as Bohr.s radius

**Question: Distinguish amongst insulators, conductors and semiconductors in terms of their energy, and band diagram.**

Answer: **Insulators **are materials that have a large energy gap between the valence and conduction bands, making them poor conductors of electricity. The band diagrams of insulators often look like a flat line between the valence and conduction bands with a large gap in between.

**Conductors **are materials with a small energy gap between the valence and conduction bands, making them excellent conductors of electricity. The band diagrams of conductors often look like a flat line between the valence and conduction bands with a very small gap in between.

**Semiconductors** are materials that have an intermediate energy gap between the valence and conduction bands, making them semiconductors of electricity. The band diagrams of semiconductors often look like a curved line between the valence and conduction bands with a moderate gap in between.

**Question: Ground wave propagation is not suitable for high frequency. Discuss.**

Answer: Ground wave propagation is a type of radio wave propagation that involves the radiation of radio waves from an antenna, which takes the form of a wave that travels along the surface of the Earth. This type of propagation is most suitable for low-frequency radio waves, which tend to have longer wavelengths and can travel large distances even in the presence of obstacles. Higher frequency radio waves, such as those in the microwave range, have shorter wavelengths and thus cannot propagate as far along the surface of the Earth. This is because the surface of the Earth acts as a dielectric material, with its conductivity and permittivity varying depending on the type of soil and its moisture content. This impedance mismatch between the air and the Earth’s surface causes the higher frequency radio waves to be reflected instead of propagating along the surface of the Earth.

** Very Short Answer Type Questions**

**Question: State two factors by which the current sensitivity of a moving coil galvanometer can be improved.**

Answer: The current sensitivity of a moving coil galvanometer can be improved by:

1. Increasing the number of turns of the coil in the galvanometer

2. Increasing the area of the coil in the galvanometer

**Question: What is wattless current**

Answer: Wattless current is an electrical current that does not involve the transfer of energy. It is a type of alternating current (AC) that passes through an electrical circuit without dissipating any energy in the form of heat or light.

Wattless current is typically used in applications such as radio frequency (RF) transmission, where the energy of the current is used to transfer information rather than to produce a useful output.

**Question: What do you mean by magnifying power of a microscope**

Answer: Magnifying power is a measure of the capability of a microscope to make an object appear larger than its actual size. It is usually expressed as a ratio of the size of the object when seen through the microscope compared to the size of the object when viewed with the naked eye. The higher the magnifying power of the microscope, the larger the magnification of the object.

**Question: Why doping is done?**

Answer: Doping is the act of adding impurities to intrinsic semiconductors to change their properties. To enable us as a p-type or n-type semiconductor in a diode, intrinsic semiconductors are doped to raise the concentration of the majority charge carrier.

** Objective Type Questions**

**Question: 1 volt is equal to ————-**

Answer: 1 volt is equal to 1 joule per coulomb of electrical charge.

**Question: Resistivity of a conductor depends on its———–**

Answer: Material or composition

**Question: Define the term Magnetic moment**

Answer: Magnetic moment is a measure of an object’s tendency to interact with a magnetic field. It is a vector quantity representing the magnitude and direction of the magnetic field generated by the object. The strength of the magnetic moment depends on the object’s size, shape, and the amount and type of material it is made from.

**Question: Transformer is based upon principle ————- field**

Answer: Electromagnetic

**Question: The sky appears blue because of —————–**

Answer: Rayleigh scattering.

**Question: A N type of semiconductor is negatively charged True/False**

Answer: True

**Question: Communication channel consists of ————-**

Answer: A communication channel consists of a medium of transmission, such as radio waves, telephone lines, or cables, that enables two or more parties to exchange information.

**Question: Modulated wave is ———–**

Answer: A wave whose parameters, such as amplitude or frequency, vary with time.