Two cells of same emf but different internal resistances \(I_{1}\) and \(I_{2}\) are connected in series with a resistance \(R\). The value of resistance \(R\), for which the potential difference across second cell is zero, is

The magnetic flux through a coil perpendicular to its plane is varying according to the relation \(\phi=\) \(\left(5 t^{3}+4 t^2+2 t-5\right) \; Weber\). If the resistant of the coil is \(5 \; ohm\), then the induced current through the coil at \(t =2 \; sec\) will be \(....\,A\)

The wavelength of an \(X-\)ray beam is \(10 \, \mathring A\). The mass of a fictitious particle having the same energy as that of the \(X-\)ray photons is \(\frac{ x }{3} h \,kg\). The value of \(x\) is ....... . \((h =\) Planck's constant \()\)

A \(1 \mathrm{~kg}\) mass is suspended from the ceiling by a rope of length \(4 \mathrm{~m}\). A horizontal force ' \(F\) ' is applied at the mid point of the rope so that the rope makes an angle of \(45^{\circ}\) with respect to the vertical axis as shown in figure. The magnitude of \(F\) is _______.

Two identical particles each of mass \(m\) go round a circle of radius \(a\) under the action of their mutual gravitational attraction. The angular speed of each particle will be

A Carnot's engine works as a refrigerator between \(250\, K\) and \(300\, K\). It receives \(500\, cal\) heat from the reservoir at the lower temperature. The amount of work done in each cycle to operate the refrigerator is ..... \(J\)

An excited \(He^+\) ion emits two photons in succession, with wavelengths \(108.5\, nm\) and \(30.4\, nm\), in making a transition to ground state. The quantum number \(n\), corresponding to its initial excited state is \(n=........\) (for photon of wavelength \(\lambda \), energy \(E = \frac{{1240\,eV}}{{\lambda \,(in\,nm)}}\))

A tube of length \(50\,cm\) is filled completely with an incompressible liquid of mass \(250\,g\) and closed at both ends. The tube is then rotated in horizontal plane about one of its ends with a uniform angular velocity \(x \sqrt{ F }\) rad \(s ^{-1}\). If \(F\) be the force exerted by the liquid at the other end then the value of \(x\) will be\(....\)

The ratio of the density of oxygen nucleus \(\left({ }_8^{16} O \right)\) and helium nucleus \(\left({ }_2^4 He \right)\) is