Question

Write notes on the following:-

a) Seismograph
b) Positive and Negative charge
c) LED
d) Audible and Inaudible sound
e) Lubricants
f) Pressure

Answer 1

pressure=> it is the force per unit area.
position charge ( anion)
negative charge ( cation)
sorry to say haan
..............

Answer 2

a. an instrument that measures and records details of earthquakes, such as force and duration.

b. The electric charge of a macroscopic object is the sum of the electric charges of the particles that make it up. ... An ion is an atom (or group of atoms) that has lost one or more electrons, giving it a net positive charge (cation), or that has gained one or more electrons, giving it a net negative charge (anion).

c. A light-emitting diode is a semiconductor light source that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. This effect is called electroluminescence. 

d. Audible sound: The human ear can only recognize sounds of frequencies in the range of 20 Hz and 20,000 Hz and this range of frequency is called audible sound. ... Inaudible sound: Sound with frequency below 20 hertz and above 20,000 hertz is called sound ofinaudible range.

e. a substance used for lubricating an engine or component, such as oil or grease.

f. continuous physical force exerted on or against an object by something in contact with it.