Two sources of equal emf are connected in series. This combination is, in turn connected to an external resistance R. The internal resistance of two sources are r₁ and r₂ (r₂ > r₁). If the potential difference across the source of internal resistance r₂ is zero, then R equals to -

Which of the following statements is correct?

The equivalent resistance between A and B of the network shown in figure is

A bar magnet has magnetic dipole moment $$\overrightarrow M $$. Its initial position is parallel to the direction of uniform magnetic field $$\overrightarrow B $$. In this position, the magnitudes of torque and force acting on it respectively are -