The resistance of wire at $$0^{\circ} \mathrm{C}$$ is $$20 \Omega$$. If the temperature coefficient of the resistance is $$5 \times 10^{-3}{ }^{\circ} \mathrm{C}^{-1}$$. The temperature at which the resistance will be double of that at $$0^{\circ} \mathrm{C}$$ is
An electron having kinetic energy of 100 eV circulates in a path of radius 10 cm in a magnetic field. The magnitude of magnetic field $$|\mathbf{B}|$$ is approximately [Mass of electron $$=0.5 \mathrm{~MeV} \mathrm{c}^{-2}$$, where c is the velocity of light].
A particle of mass $$2.2 \times 10^{-30} \mathrm{~kg}$$ and charge $$1.6 \times 10^{-19} \mathrm{C}$$ is moving at a speed of $$10 \mathrm{~km} \mathrm{~s}^{-1}$$ in a circular path of radius 2.8 cm inside a solenoid. The solenoid has $$25 \frac{\text { turns }}{\mathrm{cm}}$$ and its magnetic field is perpendicular to the plane of the particle's path. The current in the solenoid is
(Take, $$\mu_0=4 \pi \times 10^{-7} \mathrm{~Hm}^{-1}$$)
Two short magnets of equal dipole moments $$M$$ are fastened perpendicularly at their centres. The magnitude of the magnetic field at a distance $$d$$ from the centre on the bisector of the right angle is ($$\mu_0=$$ Permeability of free space)