Physics Delhi Set - 2 2023-2024 Science (English Medium) Class 12 Question Paper Solution

An ammeter and a voltmeter are connected in series to a battery. Their readings are noted as ‘A’ and ‘V’ respectively. If a resistor is connected in parallel with the voltmeter, then ______.

A will increase, V will decrease.

A will decrease, V will increase.

Both A and V will decrease.

Both A and V will increase.

An ac voltage is applied across an ideal inductor. The current in it ______.

leads the voltage by `(1/4)` cycle.

lags the voltage by `(1/4)` cycle.

leads the voltage by `(1/2)` cycle.

lags the voltage by `(1/2)` cycle.

An iron needle is kept near a strong bar magnet. It will experience ______.

a force of attraction and no torque.

a force of attraction and a torque.

a torque and no force.

neither a force nor a torque.

A galvanometer shows full scale deflection for a current I_g. If a shunt of resistance S₁ is connected to the galvanometer, it gets converted into an ammeter of range (0 - I). When resistance of the shunt is made S₂, its range becomes (0 - 2I). Then `(S_1/S_2)` is ______.

`(I + I_g)/(I - I_g)`

`(I - I_g)/(I + I_g)`

`(2I - I_g)/(I - I_g)`

`(I - I_g)/(2I - I_g)`

A coil of area of cross-section 0.5 m² is placed in a magnetic field acting normally to its plane. The field varies as B = 0.5t² + 2t, where B is in tesla and t in seconds. The emf induced in the coil at t = 1s is ______.

0.5 V

1.0 V

1.5 V

3.0 V

A pure \[\ce{Si}\] crystal having 5 × 10²⁸ atoms m⁻³ is dopped with 1 ppm concentration of antimony. If the concentration of holes in the doped crystal is found to be 4.5 × 10⁹ m⁻³, the concentration (in m⁻³) of intrinsic charge carriers in \[\ce{Si}\] crystal is about ______.

1.2 × 10¹⁵

1.5 × 10¹⁶

3.0 × 10¹⁵

2.0 × 10¹⁶

The potential energy between two nucleons inside a nucleus is minimum at a distance of about ______.

0.8 fm

1.6 fm

2.0 fm

2.8 fm

In a Young's double-slit experiment in air, the fringe width is found to be 0.44 mm. If the entire setup is immersed in water `(n = 4/3)` the fringe width will be ______.

0.88 mm

0.59 mm

0.33 mm

0.44 mm

The variation of the stopping potential (V₀) with the frequency (v) of the incident radiation for four metals A, B, C and D is shown in the figure. For the same frequency of incident radiation producing photo-electrons in all metals, the kinetic energy of photo-electrons will be maximum for metal ______.

A

B

C

D

The energy of an electron in the ground state of hydrogen atom is −13.6 eV. The kinetic and potential energy of the electron in the first excited state will be ______.

−13.6 eV, 27.2 eV

−6.8 eV, 13.6 eV

3.4 eV, −6.8 eV

6.8 eV, −3.4 eV

The electromagnetic waves used to purify water are ______.

Infrared rays

Ultraviolet rays

X-rays

Gamma rays

The focal lengths of the objective and the eyepiece of a compound microscope are 1 cm and 2 cm respectively. If the tube length of the microscope is 10 cm, the magnification obtained by the microscope for most suitable viewing by relaxed eye is ______.

250

200

150

125

Assertion (A): An alpha particle is moving towards a gold nucleus. The impact parameter is maximum for the scattering angle of 180°.

Reason (R): The impact parameter in an alpha particle scattering experiment does not depend upon the atomic number of the target nucleus.

If both Assertion (A) and Reason (R) are true and Reason (R) is correct explanation of Assertion (A).

If both Assertion (A) and Reason (R) are true and Reason (R) is not the correct explanation of Assertion (A).

If Assertion (A) is true but Reason (R) is false.

If both Assertion (A) and Reason (R) are false.

Assertion (A): In a Young's double-slit experiment, interference pattern is not observed when two coherent sources are infinitely close to each other.

Reason (R): The fringe width is proportional to the separation between the two sources.

If both Assertion (A) and Reason (R) are true and Reason (R) is correct explanation of Assertion (A).

If both Assertion (A) and Reason (R) are true and Reason (R) is not the correct explanation of Assertion (A).

If Assertion (A) is true but Reason (R) is false.

If both Assertion (A) and Reason (R) are false.

Assertion (A): Equal amount of positive and negative charges are distributed uniformly on two halves of a thin circular ring as shown in figure. The resultant electric field at the centre O of the ring is along OC.

Reason (R): It is so because the net potential at O is not zero.

If both Assertion (A) and Reason (R) are true and Reason (R) is correct explanation of Assertion (A).

If both Assertion (A) and Reason (R) are true and Reason (R) is not the correct explanation of Assertion (A).

If Assertion (A) is true but Reason (R) is false.

If both Assertion (A) and Reason (R) are false.

Assertion (A): The energy of a charged particle moving in a magnetic field does not change.

Reason (R): It is because the work done by the magnetic force on the charge moving in a magnetic field is zero.

If both Assertion (A) and Reason (R) are true and Reason (R) is correct explanation of Assertion (A).

If both Assertion (A) and Reason (R) are true and Reason (R) is not the correct explanation of Assertion (A).

If Assertion (A) is true but Reason (R) is false.

If both Assertion (A) and Reason (R) are false.

Four point charges of 1μC, −2 μC, 1 μC and −2 μC are placed at the corners A, B, C and D respectively, of a square of side 30 cm. Find the net force acting on a charge of 4 μC placed at the centre of the square.

Three point charges, 1 pC each, are kept at the vertices of an equilateral triangle of side 10 cm. Find the net electric field at the centroid of triangle.

Derive an expression for magnetic force `vecF` acting on a straight conductor of length L carrying current I in an external magnetic field `vecB`. Is it valid when the conductor is in zig-zag form? Justify.

The radius of curvature of a convex mirror is 30 cm. It forms an image of an object which is half the size of the object. Find the separation between the object and the image.

Calculate the energy released/absorbed (in MeV) in the nuclear reaction:

\[\ce{_1^1H + _1^3H -> _1^2H + _1^2H}\]

Given: \[\ce{m(_1^1H)}\] = 1.007825 μ

\[\ce{m(_1^2H)}\] = 2.014102 μ

\[\ce{m(_1^3H)}\] = 3.016049 μ

A proton of energy 1.6 MeV approaches a gold nucleus (Z = 79). Find the distance of its closest approach.

A photosensitive surface of work function 2.1 eV is irradiated by radiation of wavelength 150 nm. Calculate

1. the threshold wavelength, 
2. energy (in eV) of an incident photon, and 
3. maximum kinetic energy of emitted photoelectron.

State Lenz's Law. In a closed circuit, the induced current opposes the change in magnetic flux that produced it as per the law of conservation of energy. Justify.

A metal rod of length 2 m is rotated with a frequency 60 rev/s about an axis passing through its centre and perpendicular to its length. A uniform magnetic field of 2T perpendicular to its plane of rotation is switched-on in the region. Calculate the e.m.f. induced between the centre and the end of the rod.

State and explain Ampere’s circuital law.

Two long straight parallel wires separated by 20 cm, carry 5 A and 10 A current respectively, in the same direction. Find the magnitude and direction of the net magnetic field at a point midway between them.

Define ‘temperature coefficient of resistance’ of a metal.

Show variation of resistivity of copper as a function of temperature in a graph.

The resistance of a wire is 10 Ω at 27°C. Find its resistance at −73°C. The temperature coefficient of resistance of the material of the wire is 1.70 × 10⁻⁴°C⁻¹.

Name the part of the electromagnetic spectrum which is stopped by the face mask worn by welders. Also write the order of wavelengths in the given case.

Name the part of the electromagnetic spectrum which is used in detectors in Earth satellites. Also write the order of wavelengths in the given case.

Name the part of the electromagnetic spectrum which is used in the ‘short-wave band’ in communication. Also write the order of wavelengths in the given case.

Explain the characteristics of a p-n junction diode that makes it suitable for its use as a rectifier.

With the help of a circuit diagram, explain the workings of a full-wave rectifier.

Explain the following, giving reasons:

A doped semiconductor is electrically neutral.

Explain the following, giving reasons: 

In a p-n junction under equilibrium, there is no net current.

Explain the following, giving reasons:

In a diode, the reverse current is practically not dependent on the applied voltage.

An electron moving with a velocity `vecv = (1.0 xx 10^7 m//s)hati + (0.5 xx 10^7 m//s)hatj` enters a region of uniform magnetic field `vecB = (0.5 mT)hatj`. Find the radius of the circular path described by it. While rotating; does the electron trace a linear path too? If so, calculate the linear distance covered by it during the period of one revolution.

The critical angle for glass is θ₁ and that for water is θ₂. The critical angle for glass-water surface would be ______.
(given _aμ_g = 1.5, _aμ_w = 1.33)

less than θ₂

between θ₁ and θ₂

greater than θ₂

less than θ₁

When a ray of light of wavelength λ and frequency v is refracted into a denser medium ______.

λ and v both increase.

λ increases but v is unchanged.

λ decreases but v is unchanged.

λ and v both decrease.

The critical angle for a ray of light passing from glass to water is minimum for ______.

red colour

blue colour

yellow colour

violet colour

Three beams of red, yellow and violet colours are passed through a prism, one by one under the same condition. When the prism is in the position of minimum deviation, the angles of refraction from the second surface are r_R, r_Y and r_V respectively. Then ______.

r_V < r_Y < r_R

r_Y < r_R < r_V

r_R < r_Y < r_V

r_R = r_Y = r_V

A ray of light is incident normally on a prism ABC of refractive index `sqrt2`, as shown in figure. After it strikes face AC, it will ______.

go straight undeviated

just graze along the face AC

refract and go out of the prism

undergo total internal reflection

Which of the following is a polar molecule?

\[\ce{O2}\]

\[\ce{H2}\]

\[\ce{N2}\]

\[\ce{HCl}\]

Which of the following statements about dielectrics is correct?

A polar dielectric has a net dipole moment in absence of an external electric field which gets modified due to the induced dipoles.

The net dipole moments of induced dipoles is along the direction of the applied electric field.

Dielectrics contain free charges.

The electric field produced due to induced surface charges inside a dielectric is along the external electric field.

When a dielectric slab is inserted between the plates of an isolated charged capacitor, the energy stored in it ______.

increases and the electric field inside it also increases.

decreases and the electric field also decreases.

decreases and the electric field increases.

increases and the electric field decreases.

An air-filled capacitor with plate area A and plate separation d has capacitance C₀. A slab of dielectric constant K, area A and thickness `(d/5)` is inserted between the plates. The capacitance of the capacitor will become ______.

`[(4K)/(5K + 1)]C_0`

`[(K + 5)/(4)]C_0`

`[(5K)/(4K + 1)]C_0`

`[(K + 4)/(5K)]C_0`

Two capacitors of capacitances 2 C₀ and 6 C₀ are first connected in series and then in parallel across the same battery. The ratio of energies stored in series combination to that in parallel is ______.

`1/4`

`1/6`

`2/15`

`3/16`

A plane light wave propagating from a rarer into a denser medium, is incident at an angle i on the surface separating two media. Using Huygen’s principle, draw the refracted wave and hence verify Snell's law of refraction.

In a Young's double slit experiment, the slits are separated by 0.30 mm and the screen is kept 1.5 m away. The wavelength of light used is 600 nm. Calculate the distance between the central bright fringe and the 4^th dark fringe.

Discuss briefly diffraction of light from a single slit and draw the shape of the diffraction pattern.

An object is placed between the pole and the focus of a concave mirror. Using mirror formula, prove mathematically that it produces a virtual and an enlarged image.

Draw equipotential surfaces for an electric dipole.

Two point charges q₁ and q₂ are located at `vec r_1 and vec r_2` respectively in an external electric field `vec E`. Obtain an expression for the potential energy of the system.

The dipole moment of a molecule is 10⁻³⁰ Cm. It is placed in an electric field `vec E` of 10⁵ V/m such that its axis is along the electric field. The direction of `vec E` is suddenly changed by 60° at an instant. Find the change in the potential energy of the dipole, at that instant.

A thin spherical shell of radius R has a uniform surface charge density σ. Using Gauss’ law, deduce an expression for electric field

1. outside and
2. inside the shell.

Two long straight thin wires AB and CD have linear charge densities 10 μC/m and −20 μC/m, respectively. They are kept parallel to each other at a distance 1 m. Find magnitude and direction of the net electric field at a point midway between them.

You are given three circuit elements X, Y and Z. They are connected one by one across a given ac source. It is found that V and I are in phase for element X. V leads I by `(pi/4)` for element Y while I leads V by `(pi/4)` for element Z. Identify elements X, Y and Z.

Establish the expression for impedance of circuit when elements X, Y and Z are connected in series to an ac source. Show the variation of current in the circuit with the frequency of the applied ac source.

In a series LCR circuit, obtain the conditions under which impedance is minimum.

In a series LCR circuit, obtain the conditions under which wattless current flows in the circuit.

Describe the construction and working of a transformer and hence obtain the relation for `(v_s/v_p)` in terms of the number of turns of primary and secondary.

Discuss four main causes of energy loss in a real transformer.