The meter is defined as the distance travelled by light in 1 299 , 792 , 458 second. Why didn't people choose some easier number such as 1 300 , 000 , 000 second? Why not 1 second?

The speed of light in vacuum is 299 , 792 , 458 m s - 1 and one meter is defined as the distance travelled by light in a vacuum. As we know that, s = v t ⇒ s = 299 , 792 , 458 m s - 1 × 1 299 , 792 , 458 s ⇒ s = 1 m . This is because light is very fast in the universe, if we try to change 1 299 , 792 , 458 to 1 300 , 000 , 000 . It will make huge error in defining the standard of meter. We can't compromise with the accuracy of measurement. Second part, If we choose 1 sec to travel by the light then it will be 300 , 000 , 000 meter we won't able to make the standard meter stick because this stick will become 300 , 000 , 000 times of the meter stick which we are using today.

The meter is defined as the distance travelled by light in 1 299 , 792 , 458 second. Why didn't people choose some easier number such as 1 300 , 000 , 000 second? Why not 1 second?

The speed of light in vacuum is 299 , 792 , 458 m s - 1 and one meter is defined as the distance travelled by light in a vacuum. As we know that, s = v t ⇒ s = 299 , 792 , 458 m s - 1 × 1 299 , 792 , 458 s ⇒ s = 1 m . This is because light is very fast in the universe, if we try to change 1 299 , 792 , 458 to 1 300 , 000 , 000 . It will make huge error in defining the standard of meter. We can't compromise with the accuracy of measurement. Second part, If we choose 1 sec to travel by the light then it will be 300 , 000 , 000 meter we won't able to make the standard meter stick because this stick will become 300 , 000 , 000 times of the meter stick which we are using today.

Match the physical quantities with their correct SI units. List-I List-II (A) Planck's constant (I) kg m s - 2 (B) Torque (II) kg - 1 m 3 (C) Weight (III) m 2 kg s - 1 (D) Specific volume (IV) kg m 2 s - 2 The correct match is

A = III , B = IV , C = I , D = II

A = II , B = IV , C = I , D = III

A = IV , B = I , C = II , D = III

A = II , B = III , C = I , D = IV

Velocity v and acceleration a in two systems of units 1 and 2 are related as v 2 = n m 2 v 1 and a 2 = a 1 m n respectively. Here m and n are constants. The relations for distance and time in two systems respectively are

n 3 m 3 L 1 = L 2 and n 2 m T 1 = T 2

L 1 = n 4 m 2 L 2 and T 1 = n 2 m T 2

L 1 = n 2 m L 2 and T 1 = n 4 m 2 T 2

n 2 m L 1 = L 2 and n 4 m 2 T 1 = T 2

EASY

Earn 100

The meter is defined as the distance travelled by light in $\frac{1}{299, 792, 458}$ second. Why didn't people choose some easier number such as $\frac{1}{300, 000, 000}$ second? Why not $1$ second?

Important Questions on Units and Measurements

MEDIUM

Physics>Mechanics>Units and Measurements>Physical Quantities

The period of oscillation of a simple pendulum is

T = 2 π \sqrt{\frac{l}{g}} .

Measured value of

l

20.0 cm

, known to

1 mm

accuracy and time for

100

oscillations of the pendulum is found to be

90 s

using a wristwatch of

1 s

resolution. The accuracy in the determination of

g

EASY

Physics>Mechanics>Units and Measurements>Physical Quantities

An accurate measurement implies that

MEDIUM

Physics>Mechanics>Units and Measurements>Physical Quantities

A huge circular arc of length $4.4 ly$ subtends an angle $4 s$ at the centre of the circle. How long it would take for a body to complete $4$ revolution if its speed is $8 AU$ per second?
Given : $1 ly = 9.46 \times 10^{15} m$

$1 AU = 1.5 \times 10^{11} m$

EASY

Physics>Mechanics>Units and Measurements>Physical Quantities

A student measured the diameter of a small steel ball using a screw gauge of least count

0.001 cm .

The main scale reading is

5 mm

and zero division of the circular scale coincides with

25

divisions above the reference level. If the screw gauge has a zero error of

- 0.004 cm .

the correct diameter of the ball is__________

EASY

Physics>Mechanics>Units and Measurements>Physical Quantities

Match the physical quantities with their correct $SI$ units.

	List-I		List-II
(A)	Planck's constant	(I)	$kg m s^{- 2}$
(B)	Torque	(II)	${kg}^{- 1} m^{3}$
(C)	Weight	(III)	$m^{2} kg s^{- 1}$
(D)	Specific volume	(IV)	$kg m^{2} s^{- 2}$