Physics (Theory) Official 2022-2023 ISC (Science) ISC Class 12 Question Paper Solution

A hollow sphere of radius R has a point charge Q at its centre. Electric flux emanating from it is `phi`. If both the charge and the radius of the sphere are doubled, electric flux emanating from the sphere will ______.

remain the same

become `2phi`

become `4phi`

become `8phi`

An electric current (I) flowing through a metallic wire is gradually increased. The graph of heating power (P) developed in it versus the current (I) is ______.

A circular coil has radius ‘r', number of turns ‘N’ and carries a current ‘I’. Magnetic flux density ‘B’ at its centre is ______.

B = μ₀NI

B = `(μ_0"NI")/"2r"`

B = `(μ_0"NI")/(4πr)`

B = `(μ_0"NI")/"4r"`

If an object is placed at a distance of 10 cm in front of a concave mirror of a focal length of 20 cm, the image formed will be ______.

Real and 20 cm in front of the mirror

Real and 6.67 cm in front of the mirror.

Virtual and 20 cm behind the mirror.

Virtual and 6.67 cm behind the mirror.

What type of wavefronts are associated with a source infinity?

Cylindrical wavefronts

Plane wavefronts

Spherical wavefronts

All types of wavefronts

Matter waves are ______.

waves associated with moving particles.

waves associated with stationary particles.

waves associated with any charged particles.

waves associated with electrons only.

With an increase in the temperature, the electrical conductivity of a semiconductor ______.

decreases.

increases.

does not change.

first increases and then decreases.

What is meant by an equipotential surface?

For a metallic conductor, what is the relation between current density (J), conductivity (σ) and electric field intensity (E)?

What is motional emf? State any two factors on which it depends.

What is meant by a microscope in normal use?

In a single slit Fraunhofer diffraction experiment, how does the angular width of the central maximum change when the slit width is Increased?

Name the type of nuclear reaction that takes place in the core of the Sun.

What type of semiconductor is obtained when a crystal of silicon is doped with a trivalent element?

Calculate equivalent capacitance of the circuit shown in the Figure given below:

Calculate electric potential at a point P which is at a distance of 9 cm from a point charge of 50 μC.

Write balancing condition of a Wheatstone bridge.

Current ‘I’ flowing through a metallic wire is related to drift speed ν_d of free electrons as follows:

I = nAeν_d, 

State what the symbol ‘n’ stands for.

When an electric current is passed through a wire or a coil, a magnetic field is produced. Is the reverse phenomenon possible i.e, can a magnetic field produce an electric current? Explain with the help of an appropriate example.

A long straight wire AB carries a current of 5A. P is a proton travelling with a velocity of 2 × 10⁶ m/s, parallel to the wire, 0.2 m from it and in a direction opposite to the current, as shown in Figure below. Calculate the force which magnetic field of the current carrying conductor AB exerts on the proton.

A moving coil galvanometer of resistance 55 Ω produces a full scale deflection for a current of 250 mA. How will you convert it into an ammeter with a range of 0 - 3A?

How are electric vector `(vec "E")`, magnetic vector `(vec "B")` and velocity vector `(vec "C")` oriented in an electromagnetic wave?

Name the electromagnetic wave/radiation which is used to study crystal structure.

Name any two phenomena which take place in the formation of a rainbow.

With reference to semiconductor physics, answer the following question.

What is meant by “Forbidden band" of energy levels?

With reference to semiconductor physics, answer the following question.

In which material “Forbidden band” is absent?

Show that intensity of electric field at a point in broadside position of an electric dipole is given by:

E = `(1/(4piepsilon_0)) "p"/(("r"^2 + l^2)^(3//2))`

Where the terms have their usual meaning.

Eight identical cells, each of emf 2V and internal resistance 3 Ω, are connected in series to form a row. Six such rows are connected in parallel to form a battery. This battery is now connected to an external resistor R of resistance 6 Ω. Calculate:

1. emf of the battery.
2. internal resistance of the battery.
3. current flowing through R.

In the circuit shown in Figure below, E₁ and E₂ are batteries having emfs of 25V and 26V. They have an internal resistance of 1 Ω and 5 Ω respectively. Applying Kirchhoff’s laws of electrical networks, calculate the currents I₁ and I₂.

Using Ampere’s circuital law, obtain an expression for magnetic flux density ‘B’ at a point near an infinitely long and straight conductor, carrying a current I.

Using Huygen's wave theory of light, show that the angle of incidence is equal to the angle of reflection. Draw a neat and labelled diagram.

For any prism, obtain a relation between the angle of the prism (A), the angle of minimum deviation (δ_m) and the refractive index of its material (μ or n).

Obtain an expression for refraction at a single convex spherical surface, i.e., the relation between μ₁ (rarer medium), μ₂ (denser medium), object distance u, image distance v and the radius of curvature R.

What are the conditions for obtaining a good interference pattern? Give reasons.

In Young's double slit experiment, the distance of the 4^th bright fringe from the centre of the interference pattern is 1.5 mm. The distance between the slits and the screen is 1.5 m, and the wavelength of light used is 500 nm. Calculate the distance between the two slits.

Monochromatic light of wavelength 396 nm is incident on the surface of a metal whose work function is 1.125 eV. Calculate:

1. the energy of an incident photon in eV.
2. the maximum kinetic energy of photoelectrons in eV.

Name any two essential parts of a nuclear reactor. State the function of any one of them.

Draw a labelled circuit diagram of a full wave rectifier. Show graphically how the output voltage varies with time.

A 60 Ω resistor, a 1.0 H inductor and a 4 μF capacitor are connected in series to an ac supply generating an emf e = 300 sin (500t) V. Calculate:

1. impedance of the circuit.
2. peak value of the current flowing through the circuit.
3. phase difference between the current and the supply voltage.

An ac generator generates an emf which is given by e = 311 sin (240 πt) V. Calculate:

1. frequency of the emf.
2. r.m.s. value of the emf.

The primary coil of a transformer has 60 turns whereas its secondary coil has 3000 turns.

If a 220 V ac voltage is applied to the primary coil, how much emf is induced in the secondary coil?

The primary coil of a transformer has 60 turns whereas its secondary coil has 3000 turns.

If a current of 5A flows in the primary coil, how much current will flow in a load in the secondary coil? State the assumption you have made regarding the transformer, in this calculation.

Name the series of lines of hydrogen spectrum which lie in the ultraviolet region.

Name the series of lines of hydrogen spectrum which lie in the visible region.

How much is the angular momentum of an electron when it is orbiting in the second Bohr orbit of hydrogen atom?

With reference to Nuclear Physics, answer the following question.

What is meant by Isotopes?

With reference to Nuclear Physics, answer the following question.

Define lu (where u stands for unified atomic mass unit).

Using Bohr’s Theory of hydrogen atom, obtain an expression for the velocity of an electron in the n^th orbit of an atom.

What is meant by “binding energy per nucleon” of a nucleus?

State the significance of binding energy per nucleon.

Read the passage given below and answer the questions that follow.

1. State any one factor on which the focal length of a lens depends.
2. Give an example where a convex lens behaves like a diverging lens.
3. What type of lens is used in a camera?
4. Write an expression for magnifying power of a compound microscope when its final image lies at the least distance of distinct vision (D).
5. State any one difference between a reflecting telescope and a refracting telescope.