Question

State scientific principle involved in the following technologies.

i) Rocket.

ii) Laser

iii) Optical fibers

iv) Nuclear reactor

Answer 1

$1.$

With rockets, the action is the expelling of gas out of the engine. The reaction is the movement of the rocket in the opposite direction. To enable a rocket to lift off from the launch pad, the action, or thrust, from the engine must be greater than the mass of the rocket. In space, however, even tiny thrusts will cause the rocket to change direction.

One of the most commonly asked questions about rockets is how they can work in space where there is no air for them to push against. The answer to this question comes from the third law. Imagine the skateboard again. On the ground, the only part air plays in the motions of the rider and the skateboard is to slow them down. Moving through the air causes friction, or as scientists call it, drag. The surrounding air impedes the action-reaction

$2.$

To explain the process of light amplification in a laser requires an understanding of the energy transition phenomena in the atoms of its active medium. They include: spontaneous emission, stimulated emission/absorption and non-radiative decay. The theory of quantum mechanics states that the electrons of atoms can take different energy states

for example, with $E_1<E_2<E_3.$By quantum mechanics the lower energy level is more stable than higher energy levels, so electrons tend to occupy the lower level. Those electrons in higher energy levels decay into lower levels, with the emission of EM radiation. This process is called spontaneous emission. The radiation emitted is equal to the energy difference between the two levels.

$3.$

An optical fibre is a cylindrical dielectric waveguide (nonconducting waveguide) that transmits light along its axis, by the process of total internal reflection. The fibre consists of a core surrounded by a cladding layer, both of which are made of dielectric materials. To confine the optical signal in the core, the refractive index of the core must be greater than that of the cladding. The boundary between the core and cladding may either be abrupt, in step-index fibre or gradual, in graded-index fibre. the information (such as voice) into electrical signals firstly, then send to laser modulation of the laser beam, strengthen the light signal with the amplitude (frequency) change, and send out through the optical fibre; At the receiving end, after receiving a light signal, the detector transforms it into electrical signals, recover to original information after demodulation.

$4.$

Nuclear reactors operate on the principle of nuclear fission, the process in which a heavy atomic nucleus splits into two smaller fragments. The nuclear fragments are in very excited states and emit neutrons, other subatomic particles, and photons. The emitted neutrons may then cause new fissions, which in turn yield more neutrons, and so forth. Such a continuous self-sustaining series of fissions constitutes a fission chain reaction. A large amount of energy is released in this process, and this energy is the basis of nuclear power systems. Most of the energy of fission—approximately 85 per cent of it—is released within a very short time after the process has occurred. The remainder of the energy produced as a result of a fission event comes from the radioactive decay of fission products, which are fission fragments after they have emitted neutrons. Radioactive decay is the process by which an atom reaches a more stable state; the decay process continues even after fissioning has ceased, and its energy must be dealt with in any proper reactor design.