JEE Advanced (Assertion-Reason Type): Units & Measurement | Chapter-wise Tests for JEE Main & Advanced PDF Download

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Directions : Each of these questions contain two statements, Assertion and Reason. Each of these questions also has four alternative choices, only one of which is the correct answer.
Q.1. Assertion : Dimensional constants are the quantities whose values are constant.
Reason : Dimensional constants are dimensionless.
(a) Assertion is correct, reason is correct; reason is a correct explanation for assertion.
(b) Assertion is correct, reason is correct; reason is not a correct explanation for assertion
(c) Assertion is correct, reason is incorrect
(d) Assertion is incorrect, reason is correct.

Correct Answer is Option (c)
Dimensional constants are not dimensionless.

Q.2. 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) Assertion is correct, reason is correct; reason is a correct explanation for assertion.
(b) Assertion is correct, reason is correct; reason is not a correct explanation for assertion
(c) Assertion is correct, reason is incorrect
(d) Assertion is incorrect, reason is correct.

Correct Answer is Option (a)
As the distance of star increases, the parallax angle decreases, and great degree of accuracy is required for its measurement. Keeping in view the practical limitation in measuring the parallax angle, the maximum distance of a star we can measure is limited to 100 light year.

Q.3. Assertion : Now a days a standard metre is defined in terms of the wavelength of light.
Reason : Light has no relation with length.
(a) Assertion is correct, reason is correct; reason is a correct explanation for assertion.
(b) Assertion is correct, reason is correct; reason is not a correct explanation for assertion
(c) Assertion is correct, reason is incorrect
(d) Assertion is incorrect, reason is correct.

Correct Answer is Option (c)

Light has well defined relation with length.

Q.4. Assertion : Out of three measurements I = 0.7 m; I = 0.70 m and I = 0.700 m, the last one is most accurate.
Reason : In every measurement, only the last significant digit is not accurately known.
(a) Assertion is correct, reason is correct; reason is a correct explanation for assertion.
(b) Assertion is correct, reason is correct; reason is not a correct explanation for assertion
(c) Assertion is correct, reason is incorrect
(d) Assertion is incorrect, reason is correct.

Correct Answer is Option (b)
The last number is most accurate because it has greatest significant figure (3).

Q.5. 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) Assertion is correct, reason is correct; reason is a correct explanation for assertion.
(b) Assertion is correct, reason is correct; reason is not a correct explanation for assertion
(c) Assertion is correct, reason is incorrect
(d) Assertion is incorrect, reason is correct.

Correct Answer is Option (c)
Since zeros placed to the left of the number are never significant, but zeros placed to right of the number are significant.

Q.6. Assertion: ‘Light year’ and ‘Wavelength’ both measure distance.
Reason : Both have dimension of time.
(a) Assertion is correct, reason is correct; reason is a correct explanation for assertion.
(b) Assertion is correct, reason is correct; reason is not a correct explanation for assertion
(c) Assertion is correct, reason is incorrect
(d) Assertion is incorrect, reason is correct.

Correct Answer is Option (c)

Light year and wavelength both represent the distance, so both have dimension of length not of time.