The velocity of an electron so that its momentum is equal to that of a photon of wavelength $$660 \mathrm{~nm}$$ is
A wire of uniform cross section and resistance 4 ohms is bent in the shape of square ABCD. Point A is connected to a point $$\mathrm{P}$$ on DC by a wire AP of resistance $$1 \mathrm{ohm}$$. When a potential difference is applied between $$\mathrm{A}$$ and $$\mathrm{C}$$, the points $$\mathrm{B}$$ and $$\mathrm{P}$$ are seen to be in same potential. What is the resistance of part $$\mathrm{DP}$$ ?
The percentage increase in magnetic field $$\mathrm{B}$$ when the space within a current carrying solenoid is filled with a medium of susceptibility 0.004 is
A storage battery of emf $$28.0 \mathrm{~V}$$ and internal resistance $$0.5 \Omega$$ is being charged by a $$140 \mathrm{~V}$$ dc supply using a series resistor of $$27.5 \Omega$$. The terminal voltage of the battery during charging is