12th Physics Important 1 Mark Questions Chapter Wise (Samacheer Kalvi)

The multiple choice section of the Class 12 Physics public exam is worth securing completely, because the concepts repeat year after year and the questions are drawn tightly from the textbook evaluation sections.

Here is what actually gets asked, unit by unit.

Unit 1: Electrostatics

• Coulomb law dependence on distance and medium
• Electric field due to a dipole on the axial and equatorial lines
• Gauss law applications: field inside and outside a charged conductor or shell
• Capacitors in series and parallel, and the effect of inserting a dielectric
• Energy stored in a capacitor, and what happens when the battery stays connected versus disconnected

The capacitor-with-dielectric question is a perennial trap. Whether charge or voltage stays constant depends entirely on whether the battery is still connected, and the question always specifies it in a clause that is easy to skim past.

Unit 2: Current Electricity

• Drift velocity and its relation to current
• Temperature dependence of resistance for conductors versus semiconductors
• Kirchhoff laws and their physical basis
• Wheatstone bridge balance condition
• Potentiometer, and why it measures emf more accurately than a voltmeter

Unit 3: Magnetism and Magnetic Effects of Electric Current

• Biot-Savart law and the field at the centre of a circular loop
• Ampere circuital law applied to a solenoid or toroid
• Force on a moving charge and the direction rules
• Torque on a current loop and the moving coil galvanometer
• Classification of magnetic materials into dia, para and ferromagnetic

Magnetic material classification questions are pure recall. Learn the three sets of properties as a table and this becomes a guaranteed mark.

Unit 4: Electromagnetic Induction and Alternating Current

• Lenz law and the direction of induced current
• Self and mutual inductance
• Phase relationship between current and voltage in pure resistive, inductive and capacitive circuits
• Resonance condition in an LCR circuit
• Transformer relations and sources of energy loss

The phase questions are the most commonly missed in this unit. Fix the leads-and-lags relationships once and they stay fixed.

Unit 5: Electromagnetic Waves

• Ordering of the electromagnetic spectrum by wavelength and frequency
• Which region is used for which application
• Properties of electromagnetic waves, including transverse nature and speed in vacuum

Short unit, high return. Do not leave it out.

Unit 6: Optics

• Mirror and lens formulas with sign conventions
• Total internal reflection and critical angle
• Prism, angle of minimum deviation and dispersion
• Young double slit: fringe width and how it changes with wavelength, slit separation and medium
• Diffraction versus interference, and conditions for each
• Polarisation, Brewster law and Malus law

Fringe width questions asking what happens when the apparatus is immersed in water are very common. Wavelength decreases in the medium, and so does fringe width.

Unit 7: Dual Nature of Radiation and Matter

• Work function and threshold frequency
• Effect of intensity versus frequency on photoelectric current and stopping potential
• de Broglie wavelength and its dependence on mass and velocity

The single most tested idea here is that intensity affects the number of photoelectrons while frequency affects their maximum kinetic energy. Almost every year there is a question separating those two.

Unit 8: Atomic and Nuclear Physics

• Bohr postulates and the radius and energy of the nth orbit
• Spectral series and which lies in which part of the spectrum
• Mass defect, binding energy per nucleon and the shape of the binding energy curve
• Radioactive decay law, half life and mean life
• Nature of alpha, beta and gamma radiation

Unit 9: Semiconductor Electronics

• Intrinsic versus extrinsic, and p-type versus n-type doping
• Forward and reverse bias characteristics of a diode
• Half wave and full wave rectifier output
• Zener diode as a voltage regulator
• Logic gates and their truth tables, including NAND and NOR as universal gates

Truth table questions are free marks. Learn all seven gates properly and never lose one here.

Unit 10: Communication Systems

• Block diagram of a communication system
• Amplitude, frequency and phase modulation and their differences
• Modes of propagation: ground, sky and space wave
• Why modulation is needed at all, including the antenna size argument

Unit 11: Recent Developments in Physics

• Nanoscience definitions and scale
• Applications of nanotechnology
• Robotics classification
• Physics in medical diagnosis

Entirely factual and very short. Students skip it and lose marks that took ten minutes to secure.

How to revise this section

Do not read these lists as a checklist. Convert each bullet into a question you answer from memory, and keep a running list of the ones you fail. Timed sets of twenty questions are far more effective than an hour of reading, because they reproduce the retrieval pressure of the actual exam.

More Class 12 practice material is being added continuously on the Class 12 section.