Physics (Theory) Official 2023-2024 ISC (Science) ISC Class 12 Question Paper Solution

If potential difference between the two ends of a metallic wire is doubled, drift speed of free electrons in the wire ______.

Remains same.

Becomes double.

Becomes four times

Becomes half

A meter bridge is balanced with a known resistance (R) in the left hand gap and an unknown resistance (S) in the right hand gap. Balance point is found to be at a distance of 1 cm from the left hand side. When the battery and the galvanometer are interchanged, balance point will ______.

Shift towards left.

Shift towards right.

Remain same.

Shift towards left or right depending on the values of R and S.

Lorentz force in vector form is ______.

F = Bq v sin θ

`overset(→)(F) = q(overset(→)(v) xx overset(→)(B))`

`overset(→)(F) = q(overset(→)(B) xx overset(→)(v))`

`overset(→)(F) = overset(→)(v)(overset(→)(q) xx overset(→)(B))`

Assertion: When an electric current is passed through a moving coil galvanometer, its coil gets deflected.

Reason: A circular coil produces a uniform magnetic field around itself when an electric current is passed through it.

Both Assertion and Reason are true and Reason is the correct explanation for Assertion.

Both Assertion and Reason are true but Reason is not the correct explanation for Assertion.

Assertion is true and Reason is false.

Assertion is false and Reason is true.

When a ray of white light is incident obliquely on the first surface of a prism, then ______.

Red colour is deviated most.

Green colour is deviated most.

Yellow colour is deviated most.

Violet colour is deviated most.

The de-Broglie wavelength (λ) associated with a moving electron having kinetic energy (E) is given by ______.

`(2h)/(sqrt(2mE))`

`(2(sqrt(2mE)))/(h)`

`h/(sqrt(2mE))`

`sqrt(2mhE)`

The majority charge carriers in a P-type semiconductor are ______.

Electrons

Holes

Protons

Ions

In an electric dipole, what is the locus of a point having zero potential?

Three identical cells each of emf 'e' are connected in parallel to form a battery. What is the emf of the battery?

Three bulbs B₁ (230V, 40W), B₂ (230V, 60W) and B₃ (230V, 100W) are connected in series to a 230V supply. Which bulb glows the brightest?

Explain the meaning of the following statement:

Curie temperature for soft iron is 770°C.

What type of wavefronts are associated with a point source of light?

What is 'Pair production'?

In semiconductor physics, what is the function of a rectifier?

A hollow sphere of radius R has a point charge q at its centre. Electric flux emanating from the sphere is X. How will the electric flux change, if at all, when radius of the sphere is doubled?

A hollow sphere of radius R has a point charge q at its centre. Electric flux emanating from the sphere is X. How will the electric flux change, if at all, when charge q is replaced by an electric dipole?

In case of an infinite line charge, how does intensity of electric field at a point change, if at all, when.

1. charge on it is doubled?
2. distance of the point is halved?

What is meant by the statement: "Relative permittivity of water is 81"?

Can a body be given a charge of 2.2 × 10^-19 C? Give a reason for your answer.

What type of transformer is used in a mobile phone charger?

Why is the core of a transformer made of soft iron?

Name the electromagnetic radiation whose frequency is 10 Hz.

What is the speed of radio waves in vacuum?

Draw a labelled graph showing the variation in intensity of diffracted light with diffracting angle in a single slit Fraunhofer diffraction experiment.

The figure below is the Energy level diagram for the Hydrogen atom. Study the transitions shown and answer the following question:

1. State the type of spectrum obtained.
2. Name the series of spectrum obtained.

In a nuclear reactor, state the use of graphite rods.

In a nuclear reactor, state the use of cadmium rods.

With reference to a semiconductor diode, define the depletion region.

With reference to a semiconductor diode, define the potential barrier.

Obtain an expression for equivalent capacitance when three capacitors C₁, C₂ and C₃ are connected in series.

The figure below shows two batteries, E1 and E2, having emfs of 18V and 10V and internal resistances of 1 Ω and 2 Ω, respectively. W₁, W₂ and W₃ are uniform metallic wires AC, FD and BE having resistances of 8 Ω, 6 Ω and 10 Ω respectively. B and E are midpoints of the wires W₁ and W₂. Using Kirchhoff's laws of electrical circuits, calculate the current flowing in the wire W₃:

The Figure below shows a potentiometer circuit in which the driver cell D has an emf of 6 V and internal resistance of 2 Ω. The potentiometer wire AB is 10 m long and has a resistance of 28 Ω. The series resistance R_S is of 2 Ω.

1. The current I_p flowing in the potentiometer wire AB when the jockey (J) does not touch the wire AB.
2. emf of the cell X if the balancing length AC is 4.5 m.

Using Biot-Savart law, show that magnetic flux density 'B' at the centre of a current carrying circular coil of radius R is given by: `B = ("μ"_0I)/(2R)` where the terms have their usual meaning.

The Figure below shows an infinitely long metallic wire YY' which is carrying a current I'.

P is a point at a perpendicular distance r from it.

Using Huygen's wave theory, show that (for refraction of light):

`sin i/sin r = "constant"`

where terms have their usual meaning. You must draw a neat and labelled diagram.

In Young's double slit experiment, show that:

`β = (λ"D")/"d"`

Where the terms have their usual meaning.

The Figure below shows a ray of monochromatic light LM incident on the first surface AB of a regular (equilateral) glass prism ABC. The emergent ray grazes the adjacent surface AC. Calculate the angle of incidence. (Refractive Index of glass = 1.5)

State whether the student's response is correct or incorrect. Give a reason for your answer.

1. EXAMINER: Image formed by the lens is magnified. Reduce the size of the image.
   STUDENT moves the lens towards the object pin.

2. EXAMINER: Plot a graph of (1/v) against (1/u).
   STUDENT takes (1/v) on Y axis and (1/u) on X axis.

3. EXAMINER: Write the relation between the optical power (P) and the focal length (f) of the convex lens.
   STUDENT writes P = 2f.

In an experiment on photo electric effect, how does stopping potential change, if at all, when intensity of incident monochromatic UV radiation is increased?

Ultraviolet light is incident on metals P, Q and R, having work functions 8 eV, 2 eV and 4 eV respectively,

1. Which metal has lowest threshold frequency for photoelectric effect?
2. For which metal is the value of E_max minimum?
   (Note: E_max is maximum kinetic energy of the emitted photoelectrons.)

What is meant by forward biasing of a semiconductor diode?

Draw a labelled characteristic curve (l-V graph) for a semiconductor diode during forward bias.

A 220V, 50Hz ac source is connected to a coil having coefficient of self-induction of 1H and a resistance of 400 Ω. Calculate:

1. the reactance of the coil.
2. the impedance of the coil.
3. the current flowing through the coil.

Draw a labelled graph showing variation of impedance (Z) of a series LCR circuit Vs frequency (f) of the ac supply. Mark the resonant frequency as f₀·

When current flowing through a solenoid decreases from 5A to 0 in 20 milliseconds, an emf of 500V is induced in it.

1. What is this phenomenon called?
2. Calculate coefficient of self-inductance of the solenoid.

RMS value of an alternating current flowing in a circuit is 5A. Calculate its peak value.

State any one difference between a direct current (dc) and an alternating current (ac).

On the basis of Bohr's theory, derive an expression for the radius of the n^th orbit of an electron of hydrogen atom.

Calculate the energy released in the following nuclear fusion reaction:

\[\ce{^2_1H + ^2_1H -> ^4_2He + energy}\]

Mass of \[\ce{^2_1H = 2.014102 u}\]

Mass of \[\ce{^4_2He = 4.002604 u}\]

Calculate mass defect and binding energy per nucleon of `"_10^20 Ne`, given 

Mass of `"_10^20 Ne= 19.992397` u

Mass of `"_0^1H = 1.007825`  u

Mass of `"_0^1n = 1.008665` u

State the Bohr's postulate of angular momentum of an electron.

What is the velocity of an electron in the 3rd orbit of hydrogen atom if its velocity in the 1^st orbit is v₀?

Radius of the 1^st orbit of hydrogen atom is r₀. What will be the radius of the 4^th orbit?

Read the passage given below and answer the question that follows.

1. Rohit observed the launch of Chandrayan 3 with the help of an optical instrument. Name the instrument used by him.
2. State any one advantage of a reflecting telescope over a refracting telescope.
3. Which instrument is used to study the structure of a virus?
4. What is the ability of an optical instrument to form enlarged images called?
5. What is the difference between a compound microscope and an astronomical telescope (refracting type), as far as their lenses are concerned?

Useful Constants & Relations: