List of practice Questions

A sample of HCl gas is placed in an electric field \(3\times 10^{4}\,NC^{-1}\). The dipole moment of each HCl molecule is \(6\times 10^{-30}\,Cm\). The maximum torque that can act on a molecule is
When a metallic plate swings between the poles of a magnet
When an electrical appliance is switched on, it responds almost immediately, because
Two identical incandescent light bulbs are connected as shown in the figure. When the circuit is an AC voltage source of frequency \(f\), which of the following observations will be correct?
A transformer rated at 10 kW is used to connect a 5 kV transmission line to a 240 V circuit. The ratio of turns in the windings of the transformer is
Three resistances of \(4\Omega\) each are connected as shown in figure. If the point D divides the resistance into two equal halves, the resistance between point A and D will be
The resistance of a metal increases with increasing temperature because
In the absence of applied potential, the electric current flowing through a metallic wire is zero because
A meter bridge is used to determine the resistance of an unknown wire by measuring the balance point length \(l\). If the wire is replaced by another wire of same material but double the length and half the thickness, the balancing point is expected to be
Equal amounts of a metal are converted into cylindrical wires of different lengths (\(L\)) and cross-sectional area (\(A\)). The wire with the maximum resistance is the one, which has
If the force exerted by an electric dipole on a charge \(q\) at a distance of 1 m is \(F\), the force at a point 2 m away in the same direction will be
A solid sphere of radius \(R_1\) and volume charge density \(\rho = \frac{\rho_0}{r}\) is enclosed by a hollow sphere of radius \(R_2\) with negative surface charge density \(\sigma\), such that the total charge in the system is zero. \(\rho_0\) is a positive constant and \(r\) is the distance from the centre of the sphere. The ratio \(\frac{R_2}{R_1}\) is
A solid spherical conductor of radius \(R\) has a spherical cavity of radius \(a\) (\(a<R\)) at its centre. A charge \(+Q\) is kept at the centre. The charge at the inner surface, outer surface and at a position \(r\) (\(a<r<R\)) are respectively
A cylindrical capacitor has charge \(Q\) and length \(L\). If both the charge and length of the capacitor are doubled, by keeping other parameters fixed, the energy stored in the capacitor
In Colpitt oscillator the feedback network consists of
The reverse saturation current of p--n diode
A radio station has two channels. One is AM at 1020 kHz and the other is FM at 89.5 MHz. For good results you will use
The communication using optical fibers is based on the principle of
In nature, the electric charge of any system is always equal to
The energy stored in the capacitor as shown in Fig. (a) is \(4.5\times 10^{-6}\) J. If the battery is replaced by another capacitor of 900 pF as shown in Fig. (b), then the total energy of system is
\(^{234}\)U has 92 protons and 234 nucleons total in its nucleus. It decays by emitting an alpha particle. After the decay it becomes
The \(K_{\alpha}\) and \(K_{\beta}\) X-rays are emitted when there is a transition of electron between the levels
A certain radioactive material \(_x^AX\) starts emitting \(\alpha\) and \(\beta\) particles successively such that the end product is \(_{Z-3}^{A-8}\)A. The number of \(\alpha\) and \(\beta\) particles emitted are respectively
In the circuit shown above, an input of 1V is fed into the inverting input of an ideal Op-amp A. The output signal \(V_{out}\) will be
When a solid with a band gap has a donor level just below its empty energy band, the solid is