If an electron in a hydrogen atom jumps from the third orbit to the second orbit, it emits a photon of wavelength $$\lambda$$. When it jumps from the second to the first orbit, the corresponding wavelength of the photon will be
A solid cylinder of mass $$2 \mathrm{~kg}$$ and radius $$0.2 \mathrm{~m}$$ is rotating about its own axis without friction with angular velocity $$5 \mathrm{~rad} \mathrm{s}^{-1}$$. A particle of mass $$1 \mathrm{~kg}$$ moving with a velocity of $$5 \mathrm{~ms}^{-1}$$ strikes the cylinder and sticks to it as shown in figure.
The angular velocity of the system after the particle sticks to it will be
A neutral water molecule is placed in an electric field $$E=2.5 \times 10^4 \mathrm{NC}^{-1}$$. The work done to rotate it by $$180^{\circ}$$ is $$5 \times 10^{-25} \mathrm{~J}$$. Find the approximate separation of centre of charges.
A telescope has an objective of focal length $$60 \mathrm{~cm}$$ and eyepiece of focal length $$5 \mathrm{~cm}$$. The telescope is focussed for least distance of distinct vision $$300 \mathrm{~cm}$$ away from the object. The magnification produced by the telescope at least distance of distinct vision is