CBSE 12 Physics Question Paper-2019 by Pavan | Practice Test to Test Your Knowledge
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CBSE 12 Physics Question Paper-2019

CBSE 12 Physics Question Paper-2019

This mock test includes actual CBSE Class 12 Physics board exam questions from the year 2019, helping students understand exam trends and practice real paper format

2025-08-05
Pavan Pavan
CBSE Class 12 Physics 2019 Grade 12

Duration

30 min

Questions

30

Marking

Negative

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Questions Preview

What is the pattern of electric field lines when a point charge –Q is kept near an uncharged conducting plate?

A
Radial lines towards the charge
B
Field lines from the plate to the charge
C
No field lines near the plate
D
Random distribution of field lines

What is the ratio of radii of the circular paths described by an α-particle and a proton of the same kinetic energy passing through a magnetic field?

A
1:1
B
2:1
C
1:2
D
4:1

How does the mobility of electrons in a conductor change if the potential difference applied across the conductor is doubled, keeping the length and temperature constant?

A
It increases
B
It decreases
C
It remains the same
D
It becomes zero

What is the speed of light in a denser medium of polarising angle 30°?

A
It increases
B
It decreases
C
It remains constant
D
It becomes infinite

In sky wave mode of propagation, why is the frequency range of transmitting signals restricted to less than 30 MHz?

A
To avoid interference with other waves
B
To minimize absorption by the ionosphere
C
To ensure efficient reflection from the ionosphere
D
To increase the coverage area

Two bulbs are rated (P1, V) and (P2, V). If they are connected in series and parallel across a supply V, find the power dissipated in the two combinations in terms of P1 and P2.

A
P1 + P2
B
P1 * P2
C
(P1 + P2)/2
D
(P1 * P2)/(P1 + P2)

Calculate the radius of curvature of an equi-concave lens of refractive index 1.5, when it is kept in a medium of refractive index 1.4, to have a power of –5D.

A
5 cm
B
10 cm
C
15 cm
D
20 cm

What is the speed of light in a denser medium of polarising angle 30°?

A
It increases
B
It decreases
C
It remains constant
D
It becomes infinite

An α-particle and a proton of the same kinetic energy are allowed to pass through a magnetic field acting normal to the direction of motion. What is the ratio of the radii of their circular paths?

A
1:1
B
2:1
C
1:2
D
1:4

Why is wave theory of electromagnetic radiation not able to explain photoelectric effect? How does photon picture resolve this problem?

A
Wave theory cannot explain the energy quantization, while photon theory does
B
Wave theory cannot explain the wave-particle duality
C
Wave theory explains the photoelectric effect completely
D
Photon theory explains interference and diffraction

What is the function of the radial magnetic field when a current-carrying coil is kept in it?

A
To create a uniform magnetic field
B
To produce a torque on the coil
C
To generate an electric field in the coil
D
To increase the current in the coil

What is the expression for the torque acting on a current-carrying loop placed in a magnetic field?

A
τ = BIA sinθ
B
τ = BI cosθ
C
τ = BIL sinθ
D
τ = BIL cosθ

State Gauss's law for magnetism. Explain its significance.

A
Gauss's law states that magnetic field lines never form closed loops
B
Gauss's law states that the net magnetic flux through any closed surface is zero
C
Gauss's law states that the total magnetic charge within a volume is zero
D
Gauss's law states that the electric field outside a conductor is zero

Write the three points of differences between para-, dia-, and ferro-magnetic materials, giving one example for each.

A
Para-magnetic: weakly attracted by a magnetic field, example: aluminum; Dia-magnetic: weakly repelled by a magnetic field, example: copper; Ferro-magnetic: strongly attracted, example: iron
B
Para-magnetic: strongly attracted, example: iron; Dia-magnetic: repelled, example: water; Ferro-magnetic: weakly attracted, example: gold
C
Para-magnetic: repelled, example: copper; Dia-magnetic: weakly attracted, example: oxygen; Ferro-magnetic: strongly attracted, example: steel
D
Para-magnetic: weakly attracted, example: iron; Dia-magnetic: strongly repelled, example: lead; Ferro-magnetic: neutral, example: plastic

Define the term ‘decay constant’ of a radioactive sample. The rate of disintegration of a given radioactive nucleus is 10000 disintegrations/s and 5,000 disintegrations/s after 20 hr. and 30 hr. respectively from start. Calculate the half-life and initial number of nuclei at t = 0.

A
Half-life = 10 hours, initial nuclei = 20000
B
Half-life = 20 hours, initial nuclei = 20000
C
Half-life = 10 hours, initial nuclei = 10000
D
Half-life = 15 hours, initial nuclei = 15000

Describe the function of the three segments of an n-p-n transistor.

A
The emitter emits electrons, the base controls current flow, and the collector collects the electrons
B
The collector collects electrons, the base provides the current, and the emitter controls voltage
C
The emitter collects electrons, the base generates the current, and the collector controls voltage
D
The emitter absorbs electrons, the base controls temperature, and the collector stores charge

Draw the circuit diagram for studying the output characteristics of an n-p-n transistor in a CE configuration. Explain how the output characteristics are obtained.

A
The output characteristics are obtained by plotting the current through the collector against the collector-emitter voltage
B
The output characteristics are obtained by plotting the input voltage against the emitter current
C
The output characteristics are obtained by measuring the collector current while keeping the base current constant
D
The output characteristics are obtained by plotting the base-emitter voltage against the current

What is the expression for the modulation index in terms of the maximum and minimum amplitudes of an amplitude-modulated wave?

A
Modulation Index = (A - B)/(A + B)
B
Modulation Index = (A + B)/(A - B)
C
Modulation Index = A/B
D
Modulation Index = (B - A)/(A + B)

Why is the modulation index kept less than one in an amplitude-modulated wave?

A
To prevent overmodulation and distortion
B
To increase the transmission range
C
To decrease the power consumption
D
To maintain constant amplitude

Define the term ‘wavefront’ and verify Snell’s law of refraction when a plane wavefront is propagating from a denser to a rarer medium.

A
A wavefront is a surface of constant phase; Snell’s law explains the bending of light at the interface of two media
B
A wavefront is a surface of minimum intensity; Snell’s law is used to find the speed of light in a medium
C
A wavefront is a line joining points of equal amplitude; Snell’s law relates to the frequency of waves
D
A wavefront is a surface perpendicular to the wave; Snell’s law determines the velocity of sound waves

Define the term ‘decay constant’ of a radioactive sample. The rate of disintegration of a given radioactive nucleus is 10000 disintegrations/s and 5000 disintegrations/s after 20 hr. and 30 hr. respectively from start. Calculate the half-life and initial number of nuclei at t = 0.

A
Half-life = 10 hours, initial nuclei = 20000
B
Half-life = 15 hours, initial nuclei = 15000
C
Half-life = 20 hours, initial nuclei = 10000
D
Half-life = 5 hours, initial nuclei = 5000

Three photo diodes D1, D2, and D3 are made of semiconductors having band gaps of 2.5 eV, 2 eV, and 3 eV respectively. Which of them will not be able to detect light of wavelength 600 nm?

A
D1 and D2 will not be able to detect the light
B
D2 will not be able to detect the light
C
D3 will not be able to detect the light
D
All three diodes will detect the light

What is the expression for the torque acting on a current-carrying loop placed in a magnetic field?

A
τ = BIA sinθ
B
τ = BIL sinθ
C
τ = BIL cosθ
D
τ = BIA cosθ

What is the significance of a radial magnetic field when a current-carrying coil is placed in it?

A
It creates a uniform magnetic field that helps in generating maximum torque
B
It increases the field strength around the coil
C
It prevents the coil from rotating
D
It decreases the energy consumed by the coil

State Bohr’s quantization condition of angular momentum. Calculate the shortest wavelength of the Bracket series and state to which part of the electromagnetic spectrum it belongs.

A
The shortest wavelength belongs to the infrared spectrum
B
The shortest wavelength belongs to the ultraviolet spectrum
C
The shortest wavelength belongs to the X-ray spectrum
D
The shortest wavelength belongs to the visible spectrum

What is the formula to calculate the magnetic field intensity of an ideal solenoid?

A
B = μ₀ n I
B
B = μ₀ I / n
C
B = n μ₀ I
D
B = n / μ₀ I

What is the relationship between frequency and wavelength of electromagnetic waves?

A
Frequency is inversely proportional to wavelength
B
Frequency is directly proportional to wavelength
C
Frequency is independent of wavelength
D
Frequency is proportional to the square of wavelength

In the phenomenon of photoelectric effect, why is the photoelectron emitted only when the frequency of the incident light exceeds a certain threshold value?

A
Because the photon energy must overcome the work function of the material
B
Because the photon energy is always insufficient for the emission of photoelectrons
C
Because the wavelength must match the material’s electron wavelength
D
Because the frequency determines the speed of the emitted photoelectron

What is the significance of the de Broglie wavelength associated with a particle?

A
It describes the wave-particle duality of matter
B
It is the wavelength of the photon emitted by the particle
C
It describes the speed of the particle
D
It describes the energy of the particle

What is the relationship between the wavelength and the velocity of a wave?

A
Velocity = wavelength × frequency
B
Velocity = wavelength / frequency
C
Velocity = frequency / wavelength
D
Velocity = frequency × wavelength^2