Physics Outside Delhi Set 3 2022-2023 Science (English Medium) Class 12 Question Paper Solution

The magnitude of the electric field due to a point charge object at a distance of 4.0 m is 9 N/C. From the same charged object the electric field of magnitude, 16 N/C will be at a distance of ______.

1 m

2 m

3 m

6 m

The energy of a photon of wavelength 663 nm is ______.

6.64 × 10^-20 J

5.18 × 10^-19 J

3.0 × 10^-19 J

2.0 × 10^-20 J

An electromagnetic wave is produced by a charge ______.

moving with a constant velocity.

moving with a constant speed parallel to a magnetic field.

moving with acceleration.

at rest.

A semiconductor device is connected in series with a battery, an ammeter and a resistor. A current flows in the circuit. If. the polarity of the battery is reversed, the current in the circuit almost becomes zero. The device is a/an ______.

intrinsic semiconductor

p-type semiconductor

n-type semiconductor

p-n junction diode

Beams of electrons and protons move parallel to each other in the same direction. They ______.

attract each other.

repel each other.

neither attract nor repel.

the force of attraction or repulsion depends upon the speed of the beams.

The radius of \[\ce{^27_13X}\] nucleus is R. The radius of \[\ce{^125_53Y}\] nucleus will be ______.

`5/3R`

`(13/53)^{1"/"3}R`

`(5/3R)^{1"/"3}`

`(13/53R)^{1"/"3}`

An electric dipole of dipole moment 2 × 10^-8 C-m in a uniform electric field experiences a maximum torque of 6 × 10^-4 N-m. The magnitude of the electric field is ______.

2.2 × 10³ Vm^-1

1.2 × 10⁴ Vm^-1

3.0 × 10⁴ Vm^-1

4.2 × 10³ Vm^-1

A ray of monochromatic light propagating in the air is incident on the surface of the water. Which of the following will be the same for the reflected and refracted rays?

Energy carried

Speed

Frequency

Wavelength

A point charge q₀ is moving along a circular path of radius a, with a point charge Q at the centre of the circle. The kinetic energy of q₀ is ______.

`(q_0Q)/(4piε_0a)`

`(q_0Q)/(8piε_0a)`

`(q_0Q)/(4piε_0a^2)`

`(q_0Q)/(8piε_0a^2)`

Which one of the following metals does not exhibit emission of electrons from its surface when irradiated by visible light?

Rubidium

Sodium

Cadmium

Caesium

The current in a device varies with time t as I = 6 t, where I is in mA and t is in s. The amount of charge that passes through the device from t = 0s to t = 3s is ______.

10 mC

18 mC

27 mC

54 mC

A ray of light travels a distance of 12.0 m in a transparent sheet in 60 ns. The refractive index of the sheet is ______.

1.33

1.50

1.65

1.75

In an extrinsic semiconductor, the number density of holes is 4 × 10²⁰ m^-3. If the number density of intrinsic carriers is 1.2 × 10¹⁵ m^-3, the number density of electrons in it is ______.

1.8 × 10⁹ m^-3

2.4 × 10¹⁰ m^-3

3.6 × 10⁹ m^-3

3.2 × 10¹⁰ m^-3

Pieces of copper and of silicon are initially at room temperature. Both are heated to temperature T. The conductivity of ______.

both increases.

both decreases.

copper increases and silicon decreases.

copper decreases and silicon increases.

The formation of the depletion region in a p-n junction diode is due to ______.

movement of dopant atoms

diffusion of both electrons and holes

drift of electrons only

the drift of holes only

• Assertion (A): Diamagnetic substances exhibit magnetism.
• Reason (R): Diamagnetic materials do not have a permanent magnetic dipole moment.

Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).

Both Assertion (A) and Reason (R) are true and Reason (R) is NOT the correct explanation of Assertion (A).

Assertion (A) is true and Reason (R) is false.

Assertion (A) is false and Reason (R) is also false.

• Assertion (A): Work done in moving a charge around a closed path, in an electric field is always zero.
• Reason (R): Electrostatic force is a conservative force.

Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).

Both Assertion (A) and Reason (R) are true and Reason (R) is NOT the correct explanation of Assertion (A).

Assertion (A) is true and Reason (R) is false.

Assertion (A) is false and Reason (R) is also false.

• Assertion (A): In Young's double slit experiment all fringes are of equal width.
• Reason (R): The fringe width depends upon the wavelength of light (λ) used, the distance of the screen from the plane of slits (D) and slits separation (d).

Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).

Both Assertion (A) and Reason (R) are true and Reason (R) is NOT the correct explanation of Assertion (A).

Assertion (A) is true and Reason (R) is false.

Assertion (A) is false and Reason (R) is also false.

State how a moving coil galvanometer can be converted into an ammeter.

How are infrared waves produced?

Why are infra-red waves often called heat waves? Explain.

Give any two uses of infrared waves.

How are X-rays produced?

Write two uses of the following radiation.

X-rays

With the help of a circuit diagram, explain how a full wave rectifier gives output rectified voltage corresponding to both halves of the input ac voltage.

What happens to the interference pattern when two coherent sources are infinitely close?

What happens to the interference pattern when two coherent sources are far apart from each other?

The power of a thin lens is +5 D. When it is immersed in a liquid, it behaves like a concave lens with a focal length of 100 cm. Calculate the refractive index of the liquid. Given the refractive index of glass = 1.5.

Draw an energy band diagram for a p-type semiconductor at T > 0 K.

Answer the following giving reasons:

A p-n junction diode is damaged by a strong current.

Answer the following giving reasons:

Impurities are added to intrinsic semiconductors.

A ray of light is refracted by a glass prism. Obtain an expression for the refractive index of the glass in terms of the angle of prism A and the angle of minimum deviation δ_m.

Define Current density.

Define relaxation time.

Derive an expression for resistivity of a conductor in terms of the number density of charge carriers in the conductor and relaxation time.

A series CR circuit with R = 200 Ω and C = (50/π) µF is connected across an ac source of peak voltage ε₀ = 100 V and frequency v = 50 Hz. Calculate (a) impedance of the circuit (Z), (b) phase angle (Φ), and (c) voltage across the resistor.

A potential difference V is applied across a conductor of length l and cross-sectional area A. Briefly explain how the current density J in the conductor will be affected if

1. the potential difference V is doubled.
2. the conductor was gradually stretched to reduce its cross-sectional area to `A/2` and then the same potential difference V is applied across it.

A resistor of 50 Ω, a capacitor of `(25/pi)` µF and an inductor of `(4/pi)` H are connected in series across an ac source whose voltage (in volts) is given by V = 70 sin (100 πt). Calculate:

1. the net reactance of the circuit
2. the impedance of the circuit
3. the effective value of current in the circuit.

Use Gauss' law to derive the expression for the electric field `(vecE)` due to a straight uniformly charged infinite line of charge density λ C/m.

An infinitely long positively charged straight wire has a linear charge density λ. An electron is revolving in a circle with a constant speed v such that the wire passes through the centre, and is perpendicular to the plane, of the circle. Find the kinetic energy of the electron in terms of the magnitudes of its charge and linear charge density λ on the wire.

Draw a graph of kinetic energy as a function of linear charge density λ.

Consider two identical point charges located at points (0, 0) and (a, 0).

Is there a point on the line joining them at which the electric field is zero?

Consider two identical point charges located at points (0, 0) and (a, 0).

Is there a point on the line joining them at which the electric potential is zero?

Justify your answers for each case.

State the significance of the negative value of electrostatic potential energy of a system of charges.

Three charges are placed at the corners of an equilateral triangle ABC of side 2.0 m as shown in the figure. Calculate the electric potential energy of the system of three charges.

Define the coefficient of self-induction.

Derive the expression for the self-inductance of a long solenoid of cross sectional area A and length l, having n turns per unit length.

Calculate the self-inductance of a coil using the following data obtained when an AC source of frequency `(200/pi)` Hz and a DC source are applied across the coil.

With the help of a labelled diagram, describe the principle and working of an ac generator. Hence, obtain an expression for the instantaneous value of the emf generated.

The coil of an ac generator consists of 100 turns of wire, each of area 0.5 m². The resistance of the wire is 100 Ω. The coil is rotating in a magnetic field of 0.8 T perpendicular to its axis of rotation, at a constant angular speed of 60 radians per second. Calculate the maximum emf generated and power dissipated in the coil.

State Huygen's principle.

With the help of a diagram, show how a plane wave is reflected from a surface. Hence verify the law of reflection.

A concave mirror of focal length 12 cm forms three times the magnified virtual image of an object. Find the distance of the object from the mirror.

Draw a labelled ray diagram showing the image formation by a refracting telescope. Define its magnifying power.

Write two important limitations of a refracting telescope over a reflecting-type telescope.

The focal lengths of the objective and the eye-piece of a compound microscope are 1.0 cm and 2.5 cm respectively. Find the tube length of the microscope for obtaining a magnification of 300.

Read the following paragraph and answer the questions.

1. Explain the reason for the jumping of the ring when the switch is closed in the circuit.
2. What will happen if the terminals of the battery are reversed and the switch is closed? Explain.
3. Explain the two laws that help us understand this phenomenon.

Briefly explain various ways to increase the strength of the magnetic field produced by a given solenoid.

Read the following paragraph and answer the questions.

1. Which light beam has the highest frequency and why?
2. Which light beam has the longest wavelength and why?
3. Which light beam ejects photoelectrons with maximum momentum and why?

What is the effect of threshold frequency and stopping potential on increasing the frequency of the incident beam of light? Justify your answer.