Revision: Physical Quantities and Measurement Physics ICSE ICSE Class 6 CISCE

The average of the varying solar days, when the earth completes one revolution around the sun, is called mean solar day.

“A second is defined as 1/86400 the part of a mean solar day.”
OR
Second may also be defined “as to be equal to the duration of9,192,631,770 vibrations corresponding to the transition between two hyperfine levels of cesium – 133 atoms in the ground state.”

The time taken by the earth to complete one rotation about its own axis is called solar day.

The physical quantities like mass, length and time which do not depend on each other are known as fundamental quantities.

A standard metreis equal to 1650763.73 wavelengths in vacuum, of the radiation from krypton isotope of mass 86.

Measurement is the process of comparison of the given physical quantity with the known standard quantity of the same nature.

One year is defined as the time in which earth completes one complete revolution around the sun.

It is defined as the 1/1440 part of the mean solar day.

The standard metre is defined in terms of the speed of light, according to which one metre is the distance travelled by light in `1/(299,792,458)` of a second in the air (or vacuum).

The quantity of matter contained in a body is known as its mass.

Mass is the measure of the amount of matter in an object.

It is defined as 1/24 the part of the mean solar day.

Unit is the quantity of a constant magnitude which is used to measure the magnitudes of other quantities of the same nature.

The density of a substance is defined as the mass of a unit volume of that substance.

`"Density" = "Mass"/"Volume"`

Mass is the amount of matter contained in a body. Its unit is a kilogram (kg).

One metre is defined as the distance travelled by light in the air in  `1/(299,792,458)` of a second.

The S. I. unit of length is meter.

Multiple of metre = Kilometre (km).

Submultiple of metre = Centimetre (cm)

One kilogram (kg) is the S.I. unit of mass. It is defined as the mass of the international prototype of the kilogram, which is a platinum-iridium alloy cylinder stored at the International Bureau of Weights and Measures in France.

Mass is the measure of the amount of matter in an object. It is a fundamental property of matter and does not change with location or the object’s state.

Temperature is a parameter which tells the thermal state of a body (i.e., the degree of hotness or coldness of the body). It determines the direction of flow of heat when two bodies at different temperatures are placed in contact.

The temperature at which the pressure and volume of a gas theoretically reach zero is called absolute zero.

Coefficient of Linear expansion is equal to the change in length of a rod of length 1m when its temperature rises by 1°C.

• If no heat flows between two bodies in contact, they are said to be at the same temperature, even though their thermal energies may be different.
• The S.I. unit of temperature is kelvin (K), and absolute zero (0 K) is the temperature at which molecular motion ceases.