The decay constants of two radioactive substances X and Y are 4$$\lambda$$ and $$\lambda$$ respectively. At t = 0, a sample has the same number of two nuclei. The time taken for the ratio of number of nuclei to become $${1 \over {{e^3}}}$$ will be
What is the magnitude of the force experienced per unit length by a thin wire that carries a current of I = 10 A and is formed into a semi-circle with a radius of R = 20$$\pi$$ cm at a point O?
A long cylindrical iron core of cross-sectional area 5 cm2 is inserted into a long solenoid having 4000 turns/meter and carrying a current 5 A. The magnetic field inside the core is $$\pi$$ T. Find the pole strength developed.
A plane requires for take off a speed of 72 kmh$$-$$1, the run on the ground being 50 m. The mass of the plane is 10000 kg and the coefficient of friction between the plane and the ground is 0.2. Assume that the plane accelerates uniformly during take off. The minimum force required by the engine of the plane for take off is