Atoms — Physics STD 12 Science — Question

The coil of a moving-coil galvanometer keeps on oscillating for a long time if it is deflected and released. If the ends of the coil are connected together, the oscillation stops at once. Explain

The current generator I_g shown in figure, sends a constant current i through the circuit. The wire ab has a length l and mass m and can slide on the smooth, horizontal rails connected to I_g. The entire system lies in a vertical magnetic field B. Find the velocity of the wire as a function of time.

A nucleus with mass number A=240 and BE/A = 7.6 MeV breaks into two fragments each of A = 120 with BE/A = 8.5 MeV. Calculate the released energy.

Calculate the torque on the square plate of the previous problem if it rotates about a diagonal with the same angular acceleration.

Give the SI unit and definition of electric charge and also write down the smaller unit.

Define the term ‘linearly polarised light’.
When’ does the intensity of transmitted light become maximum, when a polaroid sheet is rotated between two crossed polaroids?

Electrons are emitted from an electron gun at almost zero velocity and are accelerated by an electric field E through a distance of 1.0m. The electrons are now scattered by an atomic hydrogen sample in ground state. What should be the minimum value of E so that red light of wavelength 656.3nm may be emitted by the hydrogen?

A capacitor of capacitance 'C' is being charged by connecting it across a dc source along with an ammeter.Will the ammeter show a momentary deflection during the process of charging? If so, how would you explain this momentary deflection and the resulting continuity of current in the circuit? Write the expression for the current inside the capacitor.

Show diagrammatically when is magnetic flux taken as:

1. Positive.
2. Negative.

The refractive index of the material of a convex lens is 1.5 and the radii of curvature of both its surfaces are equal. Prove that its focal length is equal to the radius of curvature.