📚 12th Physics Most Repeated Compulsory Sums – Tamil Nadu Board 2026

Two Marks Compulsory Sums Important – Tamil Nadu Board 2026

MOST IMPORTANT :

1. Compute the speed of electromagnetic wave in a medium if the amplitudes of electric and magnetic fields are 3 × 10⁴ N/C and 2 × 10⁻⁴ T, respectively. – (Repeated 3 times) cH5 pG275
2. Calculate the cut-off wavelength of X-rays from an X-ray tube of accelerating potential 20000 V. – (Repeated 2 times)Ch8 Pg132
3. Determine the number of electrons flowing per second through a conductor when a current of 32 A flows through it. – (Repeated 2 times)Ch2 Pg86
4. Calculate the time required for 60% of a sample of radon to undergo decay. Given T₁/₂ of radon = 3.8 days.Ch9  BB8
5. A sample of HCl gas is placed in a uniform electric field of magnitude 3 × 10⁴ N/C. The dipole moment of each HCl molecule is 3.4 × 10⁻³⁰ Cm. Calculate the maximum torque experienced by each HCl molecule.Ch1 Pg25

Chapter 2

1. In a Wheatstone’s bridge, P = 100Ω, Q = 1000Ω and R = 40Ω. If the galvanometer shows zero deflection, determine the value of ‘S’. (Ch2 Pg107)
2. If the resistance of a coil is 3Ω at 20°C and α = 0.004/°C, then determine its resistance at 100°C. (Ch2 Pg96)
3. Resistance of a material at 20°C and 400°C are 45Ω and 85Ω respectively. Find its temperature coefficient of resistivity. (Ch2 Pg97)

Chapter 4

1. A 400 mH coil of negligible resistance is connected to an AC circuit in which an effective current of 6 mA is flowing. Find out the voltage across the coil if the frequency is 1000 Hz. (Ch4 Pg242)
2. The self-inductance of an air core solenoid is 4.8mH. If its core is replaced by iron, the self-inductance becomes 1.8H. Find out the relative permeability of iron. (Ch4 Nm 13)
3. A capacitor of capacitance 10/πμF is connected across a 220 V, 50 Hz AC mains. Calculate the capacitive reactance. (Ch4 Pg242)
4. A square coil of side 30 cm with 500 turns is kept in a uniform magnetic field of 0.4 T. The plane of the coil is inclined at an angle of 30° to the field. Calculate the magnetic flux through the coil. (Ch4 Nm1)
5. A series RLC circuit which resonates at 400 kHz has an 80 µH inductor, 2000 pF capacitor, and 50Ω resistor. Calculate the Q-factor of the circuit. (Ch4 Pg250)
6. An ideal transformer has 460 and 40,000 turns in the primary and secondary coils respectively. Find the voltage developed per turn of the secondary coil if the transformer is connected to a 230 V AC main. (Ch4 231)

Chapter 6

1. The angle of minimum deviation for an equilateral prism is 37°. Find the refractive index of the material of the prism. (Ch6 Pg40)
2. Pure water has a refractive index of 1.33. What is the speed of light through it? (Ch6 Pg13)

Chapter 7

1. In Young’s double slit experiment, the two slits are 0.15 mm apart. The light source has a wavelength of 450 nm. The screen is 2m away from the slits. Find the bandwidth. (Ch7 Pg65)
2. Calculate the distance up to which ray optics is a good approximation for light of wavelength 500 nm falling on an aperture of width 0.5 mm. (Ch7 Pg74)
3. Calculate the power of the lens of the spectacles needed to rectify the defect of sightedness for a person who could see clearly up to a distance of 1.8m. (Ch7 Pg97)

Chapter 9

1. Calculate the radius of 79Au¹⁹⁷ nucleus. (Ch9 Pg165)

Chapter 10

1. The given circuit has two ideal diodes connected as shown in the figure below. Calculate the current flowing through the resistance R₁. (Ch10 Numerical 1)
2. In the combination of the below gates, write the Boolean equation for output Y in terms of inputs A and B. (Circuit diagram shown in the image.) (Ch10 Pg230)

Three Marks Compulsory Questions Important :

Most Important

1. The resistance of a nichrome wire at 20°C is 10Ω. If its temperature coefficient of resistivity of nichrome is 0.004/°C, find the resistance of the wire at the boiling point of water. Comment on the result.Ch2 nm4
2. Calculate the number of nuclei of Carbon-14 undecayed after 22,920 years if the initial number of Carbon-14 atoms is 10,000. The half-life of Carbon-14 is 5730 years.Ch9 Pg176
3. A monochromatic light is incident on an equilateral prism at an angle 30° and is emergent at an angle of 75°. What is the angle of deviation produced by the prism?Ch6 Pg39

Important

Chapter 1

1. Calculate the electric flux through the rectangle of sides 5 cm and 10 cm kept in the region of a uniform electric field 100 NC⁻¹. The angle θ is 60°. (Ch1 Pg38)

Chapter 2

1. A copper wire of 10⁻⁶ m² area of cross-section carries a current of 2 A. If the number of free electrons per cubic meter in the wire is 8 × 10²⁸, calculate the current density and the average drift velocity of electrons. (Ch2 Pg86)

Chapter 3

1. A coil of a tangent galvanometer of diameter 0.24 m has 100 turns. If the horizontal component of Earth’s magnetic field is 25 × 10⁻⁶ T, then calculate the current which gives a deflection of 60°. (Ch3 Pg160)
2. Suppose a cyclotron is operated to accelerate protons with a magnetic field of strength 1T. Calculate the frequency in which the electric field between two Dees could be reversed. (Ch3)
   (Given: mp=1.67×10−27m_p = 1.67 \times 10^{-27}mp​=1.67×10−27kg, q=1.60×10−19q = 1.60 \times 10^{-19}q=1.60×10−19C)
3. An electron moving perpendicular to a uniform magnetic field 0.500 T undergoes circular motion of radius 2.50 mm. What is the speed of the electron? (Ch3 Pg171)
4. Two materials X and Y are magnetized whose values of intensity of magnetization are 500 A/m⁻¹ and 2000 A/m⁻¹, respectively. If the magnetizing field is 1000 A/m⁻¹, then among these materials, which one can be easily magnetized?

Chapter 4

1. The self-inductance of an air-core solenoid is 4.8 mH. If its core is replaced by iron core, then its self-inductance becomes 1.8 H. Find out the relative permeability of iron.
2. Find the impedance of a series RLC circuit if the inductive reactance, capacitive reactance, and resistance are 184 Ω, 144 Ω, and 30 Ω respectively. Also, calculate the phase angle between voltage and current. (Ch4 Pg247)
3. The equation for an alternating current is given by i=77sin⁡(314t)i = 77 \sin(314 t)i=77sin(314t). Find the peak current, frequency, and time period. (Ch4 Pg237)

Chapter 6

1. Light travels from air into a glass slab of thickness 50 cm and refractive index 1.5. (Ch6 Pg14)
   • a) What is the speed of light in the glass slab?
   • b) What is the time taken by the light to travel through the glass slab?
   • c) What is the optical path of the glass slab?
2. Obtain the lens maker’s formula for a lens of refractive index n2n_2n2​, which is separating two media of refractive indices n1n_1n1​and n3n_3n3​on the left and right, respectively. (Ch6 NM5)
3. An object is placed at a certain distance from a convex lens of focal length 20 cm. Find the object distance if the image obtained is magnified 4 times.Ch6 Pg10

Chapter 9

1. Calculate the amount of energy released when 1 kg of 235U^{235}U235Uundergoes fission reaction. (Ch9 Pg181)
2. Calculate the time required for 60% of a sample of radon to undergo decay. (Ch9 NM8)

Chapter 10

1. In a transistor connected in the common base configuration, α=0.95\alpha = 0.95α=0.95, Ie=1I_e = 1Ie​=1mA. Calculate the values of IoI_oIo​and IbI_bIb​. (Ch10 Pg219)
2. In the circuit shown in the figure,What are the values of ? (Ch10 Pg221)

📚 12th Physics Ch1 – Ch11 Important 2,3 & 5 Mark Questions 2026

📚 12th Most Most Repeated Questions – Tamil Nadu Board 2026

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