Tamil Nadu Board Class 12 Physics — Important Questions 2026

A spherical conducting shell of radius R carries a surface charge density σ. A point charge +q is placed at its centre. What is the electric field at a point just outside the shell? (Given: total charge on shell = Q)

The electric potential in a region is given by V = 6x² - 4y, where V is in volts and x, y are in metres. What is the electric field vector at the point (1, 2)?

Consider the Gauss's law statement: 'The net electric flux through any closed surface equals Q_enclosed/ε₀.' Which of the following is the CORRECT interpretation?

A capacitor of capacitance 8 μF is charged to 200 V. It is then connected in parallel to an uncharged capacitor of capacitance 4 μF. What is the common potential and the loss of energy after connection?

A thin convex lens of focal length 20 cm and a concave mirror of focal length 15 cm are placed coaxially with the mirror facing the lens. Their separation is 50 cm. A point object is placed on the principal axis at 30 cm from the lens (on the side away from mirror). Where is the final image formed?

The refractive index of the material of a prism is √2 and the apex angle is 45°. For what angle of incidence will the refracted ray inside the prism graze along the second surface (angle of emergence = 90°)?

An optical fibre has core refractive index 1.6 and cladding refractive index 1.4. What is the numerical aperture (NA) of the fibre when placed in air?

A silvered plano-convex lens has its convex surface silvered. The radius of curvature of the convex surface is 20 cm and the refractive index of glass is 1.5. What is the focal length of the equivalent mirror?

A battery of emf 12 V and internal resistance 2 Ω is connected to an external resistance R. The terminal voltage is found to be 10 V. What is the value of R?

Four cells each of emf 1.5 V and internal resistance 0.5 Ω are connected in parallel. This combination is connected to an external resistance of 2 Ω. What is the total current through the external resistance?

In a meter bridge experiment, the balance point is found at 60 cm from end A when unknown resistance P is in the left gap and standard resistance Q = 10 Ω is in the right gap. If P and Q are interchanged, what will be the new balance length from end A?

In a potentiometer experiment, the balancing length for cell of emf ε₁ is 75 cm and for cell of emf ε₂ is 45 cm. If the cells are connected in series aiding (same polarity), the balancing length would be: