Class 11 Physics Cbse Chapter 2 (Unit and Measurements) Important Question and Answer

Question 1.

If the size of the atom were enlarged to the tip of the sharp pin, how large would the height of Mount Everest be?

Answer:

1010 m.

Question 2.

What does the LASER mean?

Answer:

It stands for Light Amplification by Stimulated Emission of Radiation.

Question 3.

If the Universe were shrunk to the size of the Earth, how large would the Earth be on this scale?

Answer:

1o-11 m (size of an atom.).

 Question 4.

A research worker takes 100 careful readings in an experiment. If he repeats the same experiment by taking 400 readings, then by what factor will the probable error be reduced?

Answer:

By a factor of 4.

Question 5.

What is the number of significant figures in 0.06070?

Answer:

4.

Question 6.

Which of the following reading is most accurate?

(a) 7000m,

(b) 7 × 102 m,

(c) 7 × 103 m

Answer:

(a) i.e. 7000 m.

Question 7.

The density of a cube is calculated by measuring the length of one side and its mass. If the maximum errors in the measurement of mass and length are 3% and 2% respectively, then what is the maximum possible error in the measurement of density?

Answer:

3% + 3 × 2% = 9%.

Question 8.

The mass of a body as measured by two students is given as 1.2 kg and 1.23 kg. Which of the two is more accurate and why?
Answer:
The second measurement is more accurate as it has been made to the second decimal point.

Question 9.
Do the inertial and gravitational masses of ordinary objects differ in magnitude?
Answer:
No.

Question 10.
Are S.I. units Coherent? Why?
Answer:
Yes, because all the derived units in this system can be obtained by multiplying or dividing a certain set of basic units.

Question 11.
Do A.U. And Å represents the same magnitudes of distance?
Answer:
No, 1 A.U. = 1.496 × 1011 m and 1 Å = 1010 m.

Question 12.
What does SONAR stand for?
Answer:
It stands for Sound Navigation and Ranging.

Question 13.
What is the atomic mass unit (a.m.u.)?
Answer:
It is defined as 112th of the mass of one 6C12 atom
i.e. 1 a.m.u. = 112×126.023×1023 = 1.66 × 10-27 kg

Question 14.
Which is the most accurate clock?
Answer:
Cesium atomic clock.

Question 15.
Write the S.I. units of the following physical quantities:
(a) Luminous intensity
Answer:
Candela (cd)

(b) Temperature
Answer:
Kelvin (K)

(c) Electric current
Answer:
Ampere (A)

(d) Amount of substance
Answer:
Mole (mol)

(e) Plane angle
Answer:
Radian (rd)

(f) Solid angle
Answer:
Steradian (sr)

(g) Pressure.
Answer:
Nm-2 = pascal (pa).

Question 16.
What is the difference between mN, Nm, and nm?
Answer:

• mN means.milli-newton, 1 mN = 10-3N.
• Nm means newton-meter, 1 Nm = 1 J
• nm means namometer, 1 nm = 10-9 m.

Question 17.
If x = a + bt + ct2 where x is in meter and t in seconds, what is the unit of c?
Answer:
The unit on the left-hand side is a meter so the units of ct2 should also be a meter. Since t2 has units of s2, so the unit of c is ms-2

Question 18.
Will the dimensions of a physical quantity be the same, whatever be the units in which it is measured? Why?
Answer:
Yes, the dimensions don’t depend on the system of units chosen.

Question 19.
Write the dimensions of:
(i) gravitational constant
Answer:
[M-1 L3 T2]

(ii) Plank’s constant
Answer:
[M L2 T-1]

(iii) torque
Answer:
[M L2 T2]

(iv) surface tension
Answer:
[M L0 T-2]

(v) angular momentum.
Answer:
[M L2 T-1]

Question 20.
Name at least two physical quantities each having dimensions:
(a) [M L-1 T-2]
Answer:
Pressure and stress,

(b) [M L2 T-1]
Answer:
Plank’s constant and angular momentum.

Question 21.
State the principle of homogeneity of dimensions?
Answer:
It states that the dimensions of each term on both sides of an equation are the same.

Question 22.
Which are the main types of errors in a physical measurement?
Answer:
Main errors are systematic error, random error, gross error, relative error, and percentage error.

Question 23.
Which one is large, the number of microseconds in a second or the number of seconds in a year?
The number of seconds in a year = 107s and the number of microseconds in a second = 106μs. So the number of seconds in a year is larger than microseconds in a second.

Question 24.
Do significant figures change if the physical quantity is measured in different systems of units?
Answer:
No, significant figures don’t depend on the system of units. e.s. 250 g = 2.50 × 10-1 kg.
Both have 3 significant figures.

Question 25.
Suggest a distance corresponding to each of the following order of length:
(a) 10-4 m
Answer:
Size of the atomic nucleus

(b) 10-9 m
Answer:
Size of the oil molecule

(c) 104 m
Answer:
Height of Mount Everest

(d) 107 m
Answer:
Radius of Earth

(e) 109 m.
Answer:
The radius of Sun.

Question 26.
What do you understand by the following?
(a) Century
Answer:
It is the largést unit of time, 1 century = 100 years.

(b) Shake
Answer:
It is the smallest unit of time, 1 shake = 10-8s.

(c) Lunar month
Answer:
It is the time taken by the moon to complete one revolution around the Earth, 1 lunar month = 27.3 days.

(d) Leap year
Answer:
A year that is divisible by four and in which the month of February is of 29 days is called a leap year.

(e) Tropical year.
Answer:
The year in which the total solar eclipse takes place is called a tropical year.