Class 12th

The half-life of Au¹⁹⁸ is 2.7 days. The activity of 1.50 mg of Au¹⁹⁸ if its atomic weight is 198 g mol⁻¹ is, (Nₐ = 6*10²³ / mol)

Two identical antennas on identical towers are separated from each other by a distance of 45 km. What should be the minimum height of receiving antenna to receive the signals in line of sight? (Assume radius of earth is 6400 km)

A charge Q is moving dl distance in the magnetic field B. Find the value of work done by B

Red light differs from blue light as they have:

The following logic gate is equivalent to:

Calculate the time interval between 33% decay and 67% decay if half-life of a substance is 20 minutes.

The magnetic field in a region is given by B = B₀(x/a)k. A square loop of side d is placed with its edges along the x and y axes. The loop is moved with a constant velocity v = v₀i. The emf induced in the loop is:

For changing the capacitance of a given parallel plate capacitor, a dielectric material of dielectricconstant K is used, which has the same area as the plates of the capacitor. The thickness of the dielectric slab is 3d/4 , where 'd' is the separation between the plates of parallel plate capacitor. The new capacitance (C') in terms of original capacitance (C0) is given by the following relation:

The Kα - X ray of molybdenum has wavelength 0.071 nm. If the energy of a molybdenum atom with a K electron knocked out is 27.5 keV, the energy of this atom when an L electron is knocked out will be _____ keV. (Round off to the nearest integer)
[h = 4.14 * 10⁻¹⁵ eVs, c = 3 * 10⁸ ms⁻¹]

In the given figure the magnetic flux through the loop increases according to the relation φB(t) = 10t² + 20t, where φB is in milliwebers and t is in seconds. The magnitude of current through R = 2Ω resistor at t = 5s is _____ mA.