HSEB Notes of Physics | Units and Measurement | Mechanics | Short Question Answer | Class 11

PHYSICS | HSEB NOTES | SHORT QUESTION ANSWER
UNIT 1 : MECHANICS
LESSON 1 : UNITS AND MEASUREMENT OF PHYSICAL QUANTITIES
CLASS : 11

Following are some question from Units and measurement :

Q.1. Can we tell the unit of a physical quantity from its dimension ?

Ans. => Yes, we can tell the unit of a physical quantity. For example, if a physical quantity has the dimension [M^oLT^-1], its SI-unit will be ms^-1.

Q.2. Can dimension analysis tell you that a physical relation is completely right ?

Ans. => No. it can not tell the relation completely correct. It is because that the numerical factor in the relation can not be determined.

Q.3. What is the importance if base units ?

Ans. => There are seven base units in SI-units. All the physical quantities can be expressed in terms of there base units.

Q.4. Do all the constants carry dimension ?

Ans. => No, all the constants do not carry dimensions but some constants carry dimensions. For example : G is a constant which has a dimensiion.

Q.5. Does the measurement if a physical quantity depend upon the system if units used ?

Ams. => It does not depend on the system of units. There is only change in the numerical value of the physical quantity.

Q.6. Can a physical quantities have unit but is dimensionless ?

Ams. => Yes, it is possible to have unit but no dimension. For example angle has no dimension but has the uni of radian.

Q.7. Which physical quantities have the same dimension of [ML^-1T^-2] ?

Ans. => Stress, young’s modulus and pressure.

Q.8. Is dimensionally correct equation necessarily to be a correct physical relation ? What about dimensionally wrong equation ? [HSEB 2063]

Ans. => Even if a physical relation is dimensionally correct, it doesn’t prove that the relation is completely correct. It is because the numerical factor in the relation can be wrong. Dimensionally wrong equation has no meaning.

Q.9. What are characteristics of a physical standard ?

Ans. => A physical standard must have following characteristics :

1. Invariablity
2. Accessibility
3. Indestructibility
4. reproduciblity

Q.10. Do you think that a defination of a physical quantity for which no direct method of measurement is known or given has a physical meaning ?

Ans. => Yes, the measurement may be made by indirect method.

Q.11. Can you suggest a way to measure length along a curved line ?

Ans. => The length along a curved line may be measured by the technique of trajactory or by measuring the length of string by placing it on the curved line.