Assertion & Reason Type Questions: Physical World | Physics Class 11 - NEET PDF Download

For following question, two statements are given—one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
Question 1:
Assertion (A): Energy is a scalar quantity. 
Reason (R): All conserved quantities are scalars.
(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R are true but R is NOT the correct explanation of A
(c) A is true but R is false
(d) A is false and R is also false

Correct Answer is Option (c)
Assertion is true since energy is a scalar quantity. But all conserved quantities are not necessarily scalars. The total linear momentum and total angular momentum (both vectors) of an isolated system are also conserved quantities. So, the reason is not true.

Question 2:
Assertion (A): Classical Physics mainly includes subjects like Mechanics, Electrodynamics, Optics and Thermodynamics. 
Reason (R): The macroscopic domain includes phenomena at the laboratory, terrestrial and astronomical scales.
(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R are true but R is NOT the correct explanation of A
(c) A is true but R is false
(d) A is false and R is also false

Correct Answer is Option (a)
Assertion is true since classical physics mainly includes subjects like Mechanics, Electrodynamics, Optics and Thermodynamics. Mechanics is concerned with the motion (or equilibrium) of particles, rigid and deformable bodies, and general systems of particles. Electrodynamics deals with electric and magnetic phenomena associated with charged and magnetic bodies. Optics deals with phenomena involving light. The working of telescopes and microscopes, colours exhibited by thin films, etc., are topics in optics. Thermodynamics deals with systems in macroscopic equilibrium and is concerned with changes in internal energy, temperature, entropy, etc., of the system through external work and transfer of heat. So all these are in the macroscopic domain. Therefore, the reason is also true and properly explains the assertion.

Question 3:
Assertion (A): Wireless communication technology followed the discovery of the basic laws of electricity and magnetism. 
Reason (R): Technology gives rise to new physics.
(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R are true but R is NOT the correct explanation of A
(c) A is true but R is false
(d) A is false and R is also false

Correct Answer is Option (b)
Assertion is true since the basic laws of electricity and magnetism were discovered first, and then wireless communication technology developed. The reason is also true that sometimes technology gives rise to new physics. But it is not the correct explanation of the assertion.

Question 4:
Assertion: Units of Rydberg constant R are m^-1.
Reason: It follows from Bohr’s formula , where the symbols have their usual meaning.
(a) If both the assertion and the reason are true and the reason is a correct explanation of the assertion
(b) If both the assertion and reason are true but the reason is not a correct explanation of the assertion
(c) If the assertion is true but the reason is false
(d) If both the assertion and reason are false

Correct Answer is Option (a)
We know that the Rydberg equation is:
1⁄λ = R_H (1/H²₁ − 1/H²₂)
Here, the dimension of R_H is [L⁻¹].
Hence, the unit of R_H is m⁻¹.
Rydberg constant’s unit follows directly from Bohr’s formula.

Question 5:
Assertion: Parallax method cannot be used for measuring distances of stars more than 100 light years away. 
Reason: Because parallax angle reduces so much that it cannot be measured accurately.
(a) If both the assertion and the reason are true and the reason is a correct explanation of the assertion
(b) If both the assertion and reason are true but the reason is not a correct explanation of the assertion
(c) If the assertion is true but the reason is false
(d) If both the assertion and reason are false

Correct Answer is Option (a)
Parallax angle θ = I/r.
As the distance r increases, θ reduces.
Thus, the measurement becomes inaccurate at large distances.

Question 6: 
Assertion: Number of significant figures in 0.005 is one and that in 0.500 is three.
Reason: This is because zeros are not significant.
(a) If both the assertion and the reason are true and the reason is a correct explanation of the assertion
(b) If both the assertion and reason are true but the reason is not a correct explanation of the assertion
(c) If the assertion is true but the reason is false
(d) If both the assertion and reason are false

Correct Answer is Option (c)
In a number less than one, zeros between the decimal point and the first non-zero digit are not significant. But zeros to the right of the last non-zero digit are significant. Hence, the assertion is true but the reason is false.

Question 7: 
Assertion: Out of three measurements l = 0.7 m; l = 0.70 m and l = 0.700 m, the last one is most accurate.
Reason: In every measurement, only the last significant digit is not accurately known.
(a) If both the assertion and the reason are true and the reason is a correct explanation of the assertion
(b) If both the assertion and reason are true but the reason is not a correct explanation of the assertion
(c) If the assertion is true but the reason is false
(d) If both the assertion and reason are false

Correct Answer is Option (b)
Fractional errors in the three measurements respectively are

Question 8: 
Assertion: Mass, length and time are fundamental physical quantities.
Reason: They are independent of each other.
(a) If both the assertion and the reason are true and the reason is a correct explanation of the assertion
(b) If both the assertion and reason are true but the reason is not a correct explanation of the assertion
(c) If the assertion is true but the reason is false
(d) If both the assertion and reason are false

Correct Answer is Option (a)
Mass, length and time are fundamental physical quantities as they are not derived from each other, meaning they are independent of each other.

Question 9:
Assertion: Density is a derived physical quantity. 
Reason: Density cannot be derived from the fundamental physical quantities.
(a) If both the assertion and the reason are true and the reason is a correct explanation of the assertion
(b) If both the assertion and reason are true but the reason is not a correct explanation of the assertion
(c) If the assertion is true but the reason is false
(d) If both the assertion and reason are false

Correct Answer is Option (c)
Density is a derived quantity because it can be calculated from fundamental quantities, namely mass and volume.

Question 10:
Assertion: Nowadays a standard metre is defined in terms of the wavelength of light.
Reason: Light has no relation with length.
(a) If both the assertion and the reason are true and the reason is a correct explanation of the assertion
(b) If both the assertion and reason are true but the reason is not a correct explanation of the assertion
(c) If the assertion is true but the reason is false
(d) If both the assertion and reason are false

Correct Answer is Option (c)
The assertion is true; a standard metre is now defined in terms of the wavelength of a specified spectral line of light.
The velocity of light v = νλ, where λ is wavelength and ν is frequency.
Therefore, light indeed has a relationship with length, making the reason false.