List of top Physics Questions

Briefly explain how energy is produced in stars, giving two examples of the nuclear reactions involved.
Draw energy band diagrams of n-type and p-type semiconductors at temperature \( T>0 \, \text{K} \). Show the donor/acceptor energy levels with the order of difference of their energies from the bands.
Write two differences in the patterns of double-slit interference experiment and single-slit diffraction experiment. Light waves from two pinholes illuminated by two sodium lamps do not produce interference patterns. Explain why.
Assertion (A): The minimum negative potential applied to the anode in a photoelectric experiment at which photoelectric current becomes zero, is called cut-off voltage.
Reason (R): The threshold frequency for a metal is the minimum frequency of incident radiation below which emission of photoelectrons does not take place.
A convex lens of focal length 10 cm, a concave lens of focal length 15 cm, and a third lens of unknown focal length are placed coaxially in contact. If the focal length of the combination is +12 cm, find the nature and focal length of the third lens, if all lenses are thin. Will the answer change if the lenses were thick?
A cell of emf \( E \) and internal resistance \( r \) is connected across a resistor of variable resistance \( R \). Show graphically the variation of
(a) the terminal voltage across the cell,
(b) the current supplied by the cell,
with \( R \) as it is increased from 0 to the maximum value.
Germanium crystal is doped at room temperature with a minute quantity of boron. The charge carriers in the doped semiconductor will be:
Isotones are the nuclides having:
Assertion (A): A ray of light is incident normally on the face of a prism. The emergent ray will graze along the opposite face of the prism when the critical angle at glass-air interface is equal to the angle of the prism.
Reason (R): The refractive index of a prism depends on angle of the prism.
Assertion (A): A charged particle is moving with velocity \( v \) in \( x \)-\( y \) plane, making an angle \( \theta \) (\( 0<\theta<90^\circ \)) with \( x \)-axis. If a uniform magnetic field is applied in the region, along \( y \)-axis, the particle will move in a helical path with its axis parallel to \( x \)-axis.
Reason (R): The direction of the magnetic force acting on a charged particle moving in a magnetic field is along the velocity of the particle.
A p-n junction diode is forward biased. As a result,
Out of the four options given, in which transition will the emitted photon have the maximum wavelength?
Assertion (A): EM waves do not require a medium for their propagation.
Reason (R): EM waves are transverse waves.
An alternating current is given by \( I = I_0 \cos (100\pi t) \). The least time the current takes to decrease from its maximum value to zero will be:
A metal rod of length 50 cm is held vertically and moved with a velocity in a magnetic field at the place of 0.4 G. The emf induced across the ends of the rod is:
The effective resistance between points A and B in the given circuit is:
effective resistance between points A and B
The dimensional formula of magnetic permeability \(\mu_0\) is:
The frequency of a photon of energy 1.326 eV is:
A capacitor and an inductor are connected in series across an ac source of voltage of variable frequency. The frequency is increased continuously. The nature of the circuit before and after the resonance will be:
Two horizontal plates, separated by 1 cm, are arranged one above the other. A particle of mass 5 mg and charge 2 nC is released in air between the plates. The potential difference that should be applied to the plates so that the particle remains suspended between them is:
There are two inclined surfaces of equal length inclined at an angle of \(45^\circ\) with the horizontal. One of them is rough and the other is perfectly smooth. A given body takes 2 times as much time to slide down on the rough surface than on the smooth surface. The coefficient of kinetic friction (\(\mu_k\)) between the object and the rough surface is close to :
In some appropriate units, time (t) and position (x) relation of a moving particle is given by \(t = \alpha x^2 + \beta x\). The acceleration of the particle is :

In the given circuit, the equivalent resistance between points A and D is: 

If an 18 $\Omega$ resistance wire is bent into the shape of an equilateral triangle, then the equivalent resistance across the ends of any side = ?
If the weight of an object is 200 Newtons, then the weight of the object at the midpoint between the Earth's surface and the Earth's center will be: