List of top Physics Questions

(a) State Bohr's postulates for the hydrogen atom.
(b) A hydrogen atom de-excites from level n to (n-1). Show that emitted frequency ν ∝ α/n³ for large n (α = constant).
An air-filled parallel plate capacitor (d = 1mm, C = 20pF) is charged to 4.0µC. Find work done to increase plate separation to 5mm (constant charge).
Differentiate between diffusion and drift current. Explain their role in p-n junction formation.
Who first produced and observed EM waves in the 25mm-5mm range?
A transformer has 500 primary turns and 5000 secondary turns. Input is 220V-50Hz. What's the output?
(a) Two characteristic properties of nuclear force. (b) Plot potential energy of a nucleon pair vs. separation. Two conclusions from the plot.
Coils P and Q. Current in P induces current in Q. (a) Explain the phenomenon. (b) Two factors affecting current in Q. (c) Direction of current in Q when current is in P and (i) R increases, (ii) R decreases.
A bar magnet (2.5 J/T) is aligned with a 0.32 T field. (a) Find work done to align it (i) normal, (ii) opposite to the field. (b) Find torque in both cases.
(a) Define current density. Scalar or vector? E field in a conductor (n electrons/volume, mass m, charge -e, relaxation time τ). Show j = αE, where α = ne²/mτ. (b) What's a Wheatstone bridge? Balance conditions?
Charges Q1, Q2, and Q3 are at (-d,0), (0,0), and (d,0). Q1=Q3, Q2>0. Find the nature and value of Q1 for zero potential energy.
How does conductivity of an intrinsic semiconductor vary with temperature? Show in a plot.
An object is placed 30 cm in front of a concave mirror (radius of curvature 40 cm). Find: (i) image position (ii) magnification
Two batteries (6V, 0.8Ω and 3V, 0.2Ω) are connected in series with external resistance R. Find R so that the potential difference across the 6V battery is zero.
An electron and a proton have the same wavelength λ. This implies they have the same:
Two beams (3.3 eV and 11.3 eV) illuminate a metal (work function 2.3 eV). Find the ratio of maximum electron speeds.
Electric and magnetic fields of EM waves are:
A conducting circular loop (radius shrinking at 1 mm/s) is in a uniform magnetic field B = 50 mT, plane perpendicular to the field. Find the induced emf when the radius is 4 cm.
A wire bent into circular loop A carries current I. The same wire is bent into loop B with two turns, same current. Find the ratio of magnetic fields at the centers of A to B.
Four cells (emf E, internal resistance r) are connected in series, but one is wrongly connected. Find the equivalent emf and internal resistance.
A charged sphere (radius r, surface charge density σ) has electric field E. If the radius doubles (charge density constant), what's the ratio of the old to new electric field?
What are the coherent sources of light? Can two independent sodium lamps act like coherent sources? Explain.
State Huygens’ principle. A plane wave is incident at an angle $i$ on a reflecting surface. Construct the corresponding reflected wavefront. Using this diagram, prove that the angle of reflection is equal to the angle of incidence.
The refractive index of the material of a prism is $\sqrt{2}$. If the refracting angle of the prism is $60^\circ$, find:
1. The angle of minimum deviation, and 
2. The angle of incidence.
A ray of light is incident normally on a refracting face of a prism of prism angle $A$ and suffers a deviation of angle $\delta$. Prove that the refractive index $n$ of the material of the prism is given by: \[ n = \frac{\sin(A + \delta)}{\sin A}. \]
A step-up transformer converts a low voltage into high voltage. Does it violate the principle of conservation of energy? Explain.