CBSE 12 Physics Question Paper-2018 by Pavan | Practice Test to Test Your Knowledge
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  3. CBSE 12 Physics Question Paper-2018
CBSE 12 Physics Question Paper-2018

CBSE 12 Physics Question Paper-2018

This mock test includes actual CBSE Class 12 Physics board exam questions from the year 2018, helping students understand exam trends and practice real paper format

2025-08-05
Pavan Pavan
CBSE Physics 2018 Grade 12 Class 12

Duration

50 min

Questions

50

Marking

Negative

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Questions Preview

Which mode of propagation is used by short wave broadcast services?

A
Ground wave
B
Space wave
C
Sky wave
D
Reflection wave

Four nuclei of an element undergo fusion to form a heavier nucleus, with release of energy. Which of the two—the parent or the daughter nucleus—would have higher binding energy per nucleon?

A
Parent nucleus
B
Daughter nucleus
C
Both have equal binding energy
D
Neither has binding energy

Name the electromagnetic radiations used for (a) water purification, and (b) eye surgery.

A
Ultraviolet radiation and X-rays
B
Infrared radiation and UV rays
C
Microwaves and Gamma rays
D
Gamma rays and UV rays

Draw graphs showing variation of photoelectric current with applied voltage for two incident radiations of equal frequency and different intensities. Mark the graph for the radiation of higher intensity.

A
Both currents are equal
B
The higher intensity radiation has higher current at all applied voltages
C
The higher intensity radiation has lower current
D
No current is generated

A proton and an electron travelling along parallel paths enter a region of uniform magnetic field, acting perpendicular to their paths. Which of them will move in a circular path with higher frequency?

A
The proton
B
The electron
C
Both will have the same frequency
D
Neither will move in a circular path

Two electric bulbs P and Q have their resistances in the ratio of 1 : 2. They are connected in series across a battery. Find the ratio of the power dissipation in these bulbs.

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

If light of wavelength 412·5 nm is incident on each of the metals given below, which ones will show photoelectric emission and why?

A
Na and K
B
K and Ca
C
Na, K, and Ca
D
Only Na

A 10 V cell of negligible internal resistance is connected in parallel across a battery of emf 200 V and internal resistance 38 . Find the value of current in the circuit.

A
The current will be zero.
B
The current will be the difference between the two emfs divided by the resistance.
C
The current will be proportional to the internal resistance.
D
The current will depend on the external load resistance.

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

A
Because they can be used for heat detection.
B
Because they carry energy that can be converted to heat.
C
Because they are emitted by all objects.
D
Because they are absorbed by water to create heat.

A carrier wave of peak voltage 15 V is used to transmit a message signal. Find the peak voltage of the modulating signal in order to have a modulation index of 60%.

A
9 V
B
6 V
C
8 V
D
5 V

Draw the typical input and output characteristics of an n-p-n transistor in CE configuration. Show how these characteristics can be used to determine (a) the input resistance (ri), and (b) current amplification factor ().

A
Input resistance can be calculated using the slope of the input characteristics, and current amplification factor from the ratio of output current to input current.
B
Current amplification factor can be calculated from the slope of the input characteristics, and input resistance from the output current.
C
Input resistance can be calculated from the base current, and current amplification factor from the output voltage.
D
Input resistance and current amplification factor cannot be calculated using the input and output characteristics.

A radioactive isotope has a half-life of 10 years. How long will it take for the activity to reduce to 3.125%?

A
20 years
B
25 years
C
30 years
D
35 years

Explain the processes of nuclear fission and nuclear fusion by using the plot of binding energy per nucleon (BE/A) versus the mass number A.

A
Nuclear fission involves splitting heavy nuclei, releasing energy, and nuclear fusion involves combining light nuclei, releasing energy.
B
Nuclear fusion releases energy by breaking up nuclei, and nuclear fission absorbs energy by merging light nuclei.
C
Nuclear fission releases energy by combining light nuclei, and nuclear fusion absorbs energy by splitting heavy nuclei.
D
Both nuclear fission and nuclear fusion involve splitting heavy nuclei and releasing energy.

Explain the processes of nuclear fission and nuclear fusion by using the plot of binding energy per nucleon (BE/A) versus the mass number A.

A
In nuclear fission, a heavy nucleus splits into smaller nuclei and releases energy, while in nuclear fusion, two light nuclei combine to form a heavier nucleus and release energy.
B
Both nuclear fission and nuclear fusion result in the formation of a stable nucleus with the same mass number.
C
In nuclear fusion, smaller nuclei split, and in nuclear fission, larger nuclei combine to form a stable nucleus.
D
Both nuclear fusion and fission are processes that do not release any energy.

If one of two identical slits producing interference in Young’s experiment is covered with glass, so that the light intensity passing through it is reduced to 50%, find the ratio of the maximum and minimum intensity of the fringe in the interference pattern.

A
2:1
B
1:1
C
3:1
D
1:2

A symmetric biconvex lens of radius of curvature R and refractive index 1.5 is placed on a plane mirror. An optical needle moves along the axis of the lens until its real, inverted image coincides with the needle itself. The distance from the lens is 25 cm. Find the focal length of the lens.

A
20 cm
B
25 cm
C
30 cm
D
35 cm

State Bohr’s postulate to define stable orbits in hydrogen atom. How does de Broglie’s hypothesis explain the stability of these orbits?

A
Bohr's postulate states that the electron revolves in stable orbits without radiating energy. de Broglie’s hypothesis suggests that only orbits where the circumference is an integral multiple of the electron's wavelength are stable.
B
Bohr's postulate explains electron energy levels, while de Broglie’s hypothesis shows that electrons move freely within any orbit.
C
Bohr’s postulate shows that electron orbits are always unstable, and de Broglie’s hypothesis explains the electron's ability to emit energy.
D
Bohr's postulate states that the electron stays in a fixed orbit without radiating energy, and de Broglie’s hypothesis is unrelated to this concept.

A hydrogen atom initially in the ground state absorbs a photon which excites it to the n = 4 level. Estimate the frequency of the photon.

A
2.47 × 10^14 Hz
B
3.28 × 10^15 Hz
C
4.57 × 10^14 Hz
D
6.54 × 10^15 Hz

In Young’s double-slit experiment, the distance between the slits is 0.2 mm, and the screen is placed at a distance of 1.0 m from the slits. If the wavelength of light used is 600 nm, calculate the fringe width.

A
3 mm
B
0.3 mm
C
0.5 mm
D
1 mm

What is the formula to calculate the power dissipated in a resistor when a current I flows through it?

A
P = I²R
B
P = IV
C
P = V²/R
D
P = I/R

What is the direction of the force experienced by a current-carrying conductor in a magnetic field?

A
It is perpendicular to both the magnetic field and the current.
B
It is parallel to the magnetic field.
C
It is along the direction of current.
D
It is in the direction of the magnetic field.

What is the potential energy of a system of two point charges, q1 = 2 μC and q2 = 3 μC, separated by a distance of 5 cm in vacuum?

A
0.72 J
B
1.08 J
C
2.16 J
D
3.24 J

The speed of light in a vacuum is approximately 3 × 10^8 m/s. What is the value of light's frequency if its wavelength is 600 nm?

A
5 × 10^14 Hz
B
4 × 10^14 Hz
C
3 × 10^14 Hz
D
2 × 10^14 Hz

Which of the following factors affect the rate of a chemical reaction?

A
Temperature and concentration
B
Pressure and volume
C
Surface area and concentration
D
All of the above

A current of 2 A flows through a wire of resistance 5 Ω. What is the power dissipated in the wire?

A
10 W
B
20 W
C
50 W
D
40 W

What is the formula to calculate the total capacitance of capacitors connected in series?

A
1/C_total = 1/C1 + 1/C2 + 1/C3 + ...
B
C_total = C1 + C2 + C3 + ...
C
C_total = 1/(C1 + C2 + C3)
D
C_total = C1 * C2 * C3

The electric potential at a point in space is 500 V. What is the electric field at that point?

A
Zero, because the electric field is independent of potential.
B
The electric field depends on the charge distribution.
C
The electric field is related to the gradient of potential.
D
The electric field is constant at all points.

If two capacitors of capacitance 5 μF and 10 μF are connected in series, what will be the total capacitance of the combination?

A
3.33 μF
B
7.5 μF
C
15 μF
D
2 μF

Which of the following statements is true for a current-carrying conductor placed in a magnetic field?

A
The force experienced by the conductor is proportional to the current.
B
The force depends on the angle between the conductor and the magnetic field.
C
The force is independent of the length of the conductor.
D
The force is always directed opposite to the direction of current.

What is the formula to calculate the power dissipated in a resistor when a current I flows through it?

A
P = I²R
B
P = IV
C
P = V²/R
D
P = I/R

What is the relationship between current and voltage in Ohm's Law?

A
Current is directly proportional to voltage.
B
Current is inversely proportional to voltage.
C
Current is independent of voltage.
D
Current is equal to the square of voltage.

What is the effect of increasing the temperature on the resistance of a conductor?

A
Resistance decreases with temperature.
B
Resistance increases with temperature.
C
Resistance remains unchanged with temperature.
D
Resistance first decreases and then increases with temperature.

Which type of wave is the electromagnetic wave?

A
Longitudinal wave
B
Transverse wave
C
Mechanical wave
D
None of the above

What is the unit of electric charge?

A
Ampere
B
Volt
C
Coulomb
D
Ohm

In an RL circuit, the inductance L is 10 H, and the resistance R is 5 Ω. What is the time constant?

A
2 s
B
0.5 s
C
10 s
D
0.1 s

What is the function of a capacitor in an electric circuit?

A
It stores electric charge.
B
It restricts the flow of current.
C
It increases the current.
D
It converts energy into heat.

Which of the following electromagnetic waves have the highest frequency?

A
Microwaves
B
Infrared waves
C
X-rays
D
Radio waves

What happens to the kinetic energy of a particle when its velocity is doubled?

A
The kinetic energy remains unchanged.
B
The kinetic energy is quadrupled.
C
The kinetic energy is doubled.
D
The kinetic energy is halved.

The energy stored in a capacitor is given by the equation E = ½ C V². What is the energy stored when a 10 μF capacitor is charged to 5 V?

A
0.125 J
B
0.25 J
C
0.5 J
D
1 J

The magnetic field strength at a point is measured to be 2 T. What is the magnetic force on a 1 m long conductor carrying 5 A of current placed perpendicular to the magnetic field?

A
2 N
B
5 N
C
10 N
D
1 N

Which of the following is true for a resistive circuit?

A
The current is directly proportional to voltage.
B
The current is inversely proportional to voltage.
C
The resistance decreases as the voltage increases.
D
The current is independent of voltage.

What is the total resistance in a circuit where two resistors of 4 Ω and 6 Ω are connected in parallel?

A
2.4 Ω
B
10 Ω
C
1.5 Ω
D
10/3 Ω

In a moving coil galvanometer, what is the effect of increasing the number of turns in the coil?

A
The sensitivity increases.
B
The sensitivity decreases.
C
The galvanometer becomes less sensitive.
D
The resistance of the coil decreases.

In a transformer, the number of turns in the primary coil is 1000, and the number of turns in the secondary coil is 500. If the input voltage is 220 V, what is the output voltage?

A
110 V
B
220 V
C
440 V
D
330 V

What is the unit of inductance?

A
Ohm
B
Farad
C
Henry
D
Tesla

What is the magnetic field around a long straight conductor carrying current given by?

A
B = μ₀I / 2πr
B
B = μ₀I / r
C
B = μ₀r / I
D
B = μ₀r / 2πI

What is the unit of electric field strength?

A
Volt
B
Newton per Coulomb
C
Coulomb
D
Joule

What is the effect of increasing the frequency of an AC voltage applied to a capacitor?

A
The current through the capacitor decreases.
B
The current through the capacitor increases.
C
The current remains unchanged.
D
The voltage across the capacitor increases.

In a parallel plate capacitor, what is the effect of decreasing the distance between the plates on its capacitance?

A
Capacitance decreases.
B
Capacitance increases.
C
Capacitance remains unchanged.
D
Capacitance first increases and then decreases.

What happens to the total resistance when resistors are connected in parallel?

A
The total resistance increases.
B
The total resistance decreases.
C
The total resistance remains constant.
D
The total resistance is zero.