Electromagnetic Waves — Physics STD 12 Science — Question

The half-life of   is 100μs. The time taken for the radioactivity of a sample of   to decay to 1/16^th of its initial value is

(a) 400 μs

(b) 6.3 μs

(c) 40 μs

(d) 300 μs

Which one of the following has maximum refractive index ?

A charged particle moves in a uniform magnetic field. The velocity of the particle at some instant makes an acute angle with the magnetic field. The path of the particle will be

(a) A straight line	(b) A circle
(c) A helix with uniform pitch	(d) A helix with non-uniform pitch

Which of the following quantities related to a lens depend on the wavelength or wavelengths of the incident light?

1. Power.
2. Focal length.
3. Chromatic aberration.
4. Radii of curvature.

The oscillating electric and magnetic vectors of an electromagnetic wave are oriented along

(a) The same direction but differ in phase by 90°

(b) The same direction and are in phase

(c) Mutually perpendicular directions and are in phase

(d) Mutually perpendicular directions and differ in phase by 90°

A thin metal plate P is inserted between the plates of a parallel-plate capacitor of capacitance C in such a way that its edges touch the two plates (figure). The capacitance now becomes:

The value of stopping potential in the following diagram

(a) – 4V

(b) – 3 V

(c) – 2V

(d) – 1 V

A cell of e.m.f 1.5 V having a finite internal resistance is connected to a load resistance of 2Ω. For maximum power transfer the internal resistance of the cell should be

(a) 4 ohm

(b) 0.5 ohm

(c) 2 ohm

(d) None of these

Consider the following statements regarding series grouping of capacitors and select the correct statements.

1. Charge on each capacitor remains same and equals to the main charge supplied by the battery.
2. Potential difference and energy distributes in the reverse ratio of capacitance.
3. Effective capacitance is even less than the least of teh individual capacitances.

In  solution when electric current equal to 2.5 faraday is passed, the gm equivalent deposited on the cathode is

(a) 1

(b) 1.5

(c) 2

(d) 2.5