Magnetism — Physics STD 12 Science — Question

Assertion  :   X-rays are used for studying the structure of crystals.
Reason      : The distance between the atoms of crystals is of the order of wavelength of X-rays.(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.(c) If assertion is true but reason is false.(d) If the assertion and reason both are false.

Energy required for the electron excitation in Li++ from the first to the third Bohr orbit is:

Two identical coaxial circular loops carry current i each circulating in the clockwise direction. If the loops are approaching each other, then              (a) Current in each loop increases(b) Current in each loop remains the same(c) Current in each loop decreases(d) Current in one-loop increases and in the other it decreases

In a semiconductor:

Which of the following statements is incorrect about hysteresis(a) This effect is common to all ferromagnetic substances(b) The hysteresis loop area is proportional to the thermal energy developed per unit volume of the material(c) The hysteresis loop area is independent of the thermal energy developed per unit volume of the material(d) The shape of the hysteresis loop is characteristic of the material

Carbon has __________ isotopes.

Assertion  : Density of all the nuclei is same.
Reason      : Radius of nucleus is directly proportional to the cube root of mass number.(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.(c) If assertion is true but reason is false.(d) If the assertion and reason both are false.

In rear-wheel drive cars, the engine rotates the rear wheels and the front wheels rotate only because the car moves. If such a car accelerates on a horizontal road, the friction:

1. On the rear wheels is in the forward direction.
2. On the front wheels is in the backward direction.
3. On the rear wheels has larger magnitude than the friction on the front wheels.
4. On the car is in the backward direction.

To make P type semiconductor in silicon :