Wave Optics — Physics STD 12 Science — Question

A source of electromotive force (emf) is a:

Two identical charged spherical drops each of capacitance C merge to form a single drop. The resultant capacitance is(a) Equal to 2C (b) Greater than 2C (c) Less than 2C but greater than C(d) Less than C

If we double the radius of a coil keeping the current through it unchanged, then the magnetic field at any point at a large distance from the centre becomes approximately:

A radioactive element emits 200 particles per second. After three hours 25 particles per second are emitted. The half life period of element will be(a) 50 minutes(b) 60 minutes(c) 70 minutes(d) 80 minutes

In order to increase the capacity of a parallel plate condenser, one should introduce a sheet of between the plates (assume that the space is completely filled).

The shape of the wavefront of the portion of the wavefront of light from a distant star intercepted by the earth is

The ozone layer in the atmosphere absorbs:

The Bohr radius of the fifth electron of phosphorus (atomic number = 15) acting as dopant in silicon (relative dielectric constant = 12) is(a) 10.6 Å(b) 0.53 Å(c) 21.2 Å                                           (d) None of these

A solid is completely immersed in a liquid. The force exerted by the liquid on the solid will.

1. Increase if it is pushed deeper inside the liquid.
2. Change if its orientation is changed.
3. Decrease if it is taken partially out bf the liquid.
4. Be in the vertically upward direction.

You are given a resistance wire of length 50 cm and a battery of negligible resistance. In which of the following cases is largest amount of heat generated(a) When the wire is connected to the battery directly(b) When the wire is divided into two parts and both the parts connected to the battery in parallel(c) When the wire is divided into four parts and all the four connected to the battery in parallel(d) When only half the wire is connected to the battery