Question

Which of the following does not depict the correct link between technology and physics?
A. Photocell-photoelectric effect
B. Rocket propulsion- Laws of thermodynamics
C. Optical fibres- Total internal reflection of light
D. Fusion test reactor- Magnetic Confinement of plasma

Answer 1

Hint: As per the question, one of the options, which doesn’t work on their given corresponding laws, and the correct option works on Newton's law of motion. It causes an equal and opposite reaction in the remaining matter.

Complete answer:
In option (A): The photoelectric effect of light is used in photocells. Photocells are modern devices that make advantage of the photoelectric effect. These devices consist of a metal plate that emits electrons when light touches it, as well as another metal plate. The electron gets or loses energy as it passes between these plates, depending on the voltage applied to the plates.

In option (C): Optical fibres work on the principle of complete internal reflection, which is an important feature of light. It is used to collect light that is passed through an optical fibre and confine it to the fiber's core. It will be reflected back into the core of the fibre and sent to the fiber's end if it is below that angle.

In option (D): Magnetic confinement of the plasma is used in the fusion test reactor. The fusion test reactor was a well-known magnetic plasma experiment. Magnetic confinement fusion is a method of generating thermonuclear fusion power in which fusion fuel is contained in the form of a plasma by magnetic fields. To overcome the electrical repulsion between the nuclei, a temperature of tens of millions of degrees must be reached, resulting in a plasma.

In option (B): The laws of thermodynamics are not used in rocket propulsion; instead, Newton's law of motion is used. The same fundamental concept underpins the propulsion of all rockets, jet engines, deflated balloons, and even squids and octopuses: Newton's third law of motion. When matter is ejected violently from a system, it causes an equal and opposite reaction in the remaining matter. The recoil of a pistol is another classic example.Therefore, the rocket propulsion doesn’t work on the laws of thermodynamics.

Hence, the correct option is B.

Note: The principle of conservation of momentum governs the rocket's operation. The rocket ejects gases in a backward direction, creating momentum for the gases in the backward direction, and so the rocket gains momentum in the forward direction, causing it to go ahead.