NEET 2026 (Phase 1) · PhysicsThresholdPrevious Year Question
For a metal of work function 6.6 eV, which of the following wavelengths of incident radiation does NOT give rise to the photoelectric effect? (Take Planck's constant as 6.6 × 10⁻³⁴ J·s)
- A.100 nm
- B.150 nm
- C.200 nm✓
- D.50 nm
Correct Answer
(C) 200 nm
Solution & Explanation
Answer: (c) 200 nm Solution: Threshold wavelength λ₀ = hc/W = (6.6×10⁻³⁴ × 3×10⁸)/(6.6×1.6×10⁻¹⁹) ≈ 187.5 nm. Emission occurs only for λ < λ₀ ≈ 187.5 nm. 200 nm > 187.5 nm ⇒ no photoelectric effect.
🎯
Practice NEET 2026 (Phase 1) Physics — free, with instant solutions
10,000+ NEET PYQs solved step-by-step, chapter-wise, in the MedicNEET app.
More NEET PYQ solutions
PhysAn electric dipole with dipole moment 5 × 10⁻⁶ C·m is aligned with the direction of a uniform electric field of magnitude 4 × 10⁵ N/C. The dipole is then rotated through an angle of 60° with respect to the electric field. The change in the potential energy of the dipole is:PhysTwo identical charged conducting spheres A and B have their centres separated by a certain distance. Charge on each sphere is q and the force of repulsion between them is F. A third identical uncharged conducting sphere is brought in contact with sphere A first and then with B and finally removed from both. New force of repulsion between spheres A and B (radii negligible vs separation, treated as point charges) is best given as:PhysThe plates of a parallel plate capacitor are separated by d. Two slabs of different dielectric constant K1 and K2 with thickness 3d/8 and d/2 respectively are inserted in the capacitor. Due to this, the capacitance becomes two times larger than when there is nothing between the plates. If K1/K2 = 1.25, the value of K1 is:PhysA sphere of radius R is carved out of a uniform solid sphere of radius 2R (internally tangent, so its centre is at distance R from the big centre). The ratio of the moment of inertia of the small sphere to that of the remaining part, both about the Y-axis through the big sphere's centre, is:PhysThe Sun rotates once in 27 days. If it expanded to twice its present radius (uniform-density sphere, no external influence), its new period would be about:PhysA uniform rod of mass 20 kg and length 5 m leans against a smooth vertical wall, making 60° with the wall; its lower end rests on a rough horizontal floor. The friction force exerted by the floor is: (g = 10 m/s²)PhysA bob of mass m is suspended by a light string of length l and given a horizontal velocity v₀ at the lowest point. The string goes slack at a point P where it makes an angle θ above the horizontal. The ratio of the speed v at P to the initial speed v₀ is:PhysA ball of mass 0.5 kg is dropped from a height of 40 m. It hits the ground and rebounds to a height of 10 m. The impulse imparted to the ball during its collision with the ground is (g = 9.8 m/s²):