List of top Physics Questions

Under what conditions the
• [(i)] impedance of the circuit is minimum?
• [(ii)] wattless current flows in the circuit?
Two copper wires having their radii in the ratio of \(3:2\) are connected in series across a battery. Find the ratio of the drift velocities of the electrons in the wires.
Derive an expression for the capacitance of a parallel plate capacitor of plate area \(A\) and plate separation \(d\) with air present between the plates.
An electric field \(E\) is established across the ends of a cylindrical conductor of length \(L\) and area of cross-section \(A\). Discuss how electrons attain an average velocity, independent of time. Hence, obtain a relation between current in the conductor and this ‘average velocity’ of electrons.
Two air-filled capacitors of capacitances \(C_1\) and \(C_2\) are connected in parallel with a dc battery. After the capacitors are fully charged, a slab of dielectric constant \(K\) is inserted between the plates of each capacitor. How will the
• [(i)] charge on each capacitor, and
• [(ii)] energy stored in the capacitors be affected after the slab is introduced?
A series combination of \(L\), \(C\) and \(R\) is connected to an a.c. source. Using a phasor diagram, derive an expression for the impedance of the circuit and phase difference between \(V\) and \(I\).
Write two advantages of reflecting telescope over refracting telescope.
Draw a labelled ray diagram of a refracting telescope when it forms image of a distant object at infinity. Derive the expression for its magnifying power.
In a telescope the objective has much larger aperture than the eyepiece. Why?
What are coherent sources? Why are they necessary for observing stable interference pattern? Draw a graph showing the variation of intensity of light with the position on the screen in Young’s double-slit experiment.
Find the intensity of light at a point on the screen when two interfering waves of the same intensity \((I_0)\) have a path difference of
(i) \(\frac{\lambda}{4}\)
(ii) \(\frac{\lambda}{3}\)
Prove that, in Bohr model of hydrogen atom as principal quantum number \(n\) becomes large, the energy levels get closer and closer.
Derive an expression for the magnetic field \(B\), due to a circular coil of \(N\) turns, each of radius \(r\) carrying current \(I\), at a distance \(x\) from the centre along its axis.
Explain the statement: “Current is a scalar although we represent current with an arrow”.
Use Kirchhoff’s rules to find the current through \(3\,\Omega\) resistor in the circuit shown in the figure.
How does the size of a nucleus depend on its mass number A? Hence prove that the density of nucleus is a constant, independent of A, for all nuclei.
Define mutual inductance of a pair of coils. Write its SI unit.
Name the electromagnetic waves which are used for (i) detection of fractures in bones
(ii) physiotherapy
(iii) radar systems
Also write their wavelength range.
Two point charges \(-q\) and \(+q\) are located at points \((-a, 0, 0)\) and \((a, 0, 0)\) respectively. Find the electrostatic potential at point \((x, 0, 0)\) where \(x \gg a\).
A long solenoid of radius \(R\) and length \(L\) has \(n\) turns per unit length. A circular loop of radius \(r(<R)\) is placed inside at the centre of the solenoid such that its axis coincides with the axis of the solenoid. Obtain the mutual inductance of the solenoid and the loop.
Two long straight parallel conductors A and B carrying steady currents \(I_a\) and \(I_b\) in the same direction are separated by a distance \(d\). Deduce the expressions for the force acting on length \(L\) of conductor B due to conductor A and show it in figure. Write the expression for the force acting on length \(L\) of conductor A due to conductor B and show that it follows Newton’s third law.
An electric field \( \vec{E} = E_0 \hat{i} \) exists in a region of space. Draw three equipotential surfaces in the region.
State Bohr’s second postulate and mention its significance.
Consider the following nuclides : \(^{12}_{6}C,\ ^{198}_{80}Hg,\ ^{14}_{6}C,\ ^{197}_{79}Au\). Group them into isotopes and isotones.
Write two points of difference between intrinsic and extrinsic semiconductors.