Competency Based Questions,Ch1- Measurement and Experimentation

📘 Competency Based Questions

Q1.
Assertion: The unit of speed is a derived unit.
Reason: Derived units cannot be related to fundamental units.

(a) Both true, correct explanation
(b) Both true, not explanation
(c) A false, R true
(d) A true, R false

The assertion is true because speed is derived from fundamental quantities (distance and time). The reason is false because derived units can be expressed in terms of fundamental units. Therefore, the correct option is (d).

Q2.
Assertion: Smaller the least count of an instrument, more precise is the measurement.
Reason: Least count is the smallest value that can be measured accurately by an instrument.

(a) Both true, correct explanation
(b) Both true, not explanation
(c) A false, R true
(d) A true, R false

Both the assertion and the reason are true, and the reason correctly explains the assertion. A smaller least count allows finer measurements, thus increasing precision. Hence, the correct option is (a).

Q3.
Assertion: The least count of a screw gauge can be decreased by increasing pitch and decreasing circular scale divisions.
Reason: Least count is directly proportional to the pitch of the screw gauge.

(a) Both true, correct explanation
(b) Both true, not explanation
(c) A false, R true
(d) A true, R false

The assertion is false because increasing pitch actually increases the least count. The reason is true since least count is directly proportional to pitch. Therefore, the correct option is (c).

Q4.
Assertion: A pendulum clock goes slow when taken to mines.
Reason: This is due to increase in the value of acceleration due to gravity (g).

(a) Both true, correct explanation
(b) Both true, not explanation
(c) A false, R true
(d) A true, R false

The assertion is true because in mines the value of g decreases, causing the time period of the pendulum to increase, so the clock runs slow. The reason is false because g actually decreases, not increases. Hence, the correct option is (d).

Case Study 1 (Measurement)
Ayush measured the length of a metal rod as 25.4 cm using instrument A. Reema measured the same rod as 25.36 cm using instrument B.

(b) Why did Ayush and Reema get different values?

They obtained different values because the instruments used have different least counts. An instrument with a smaller least count provides more precise measurements, resulting in more decimal places.

(c) Which measuring instrument is more accurate?

Instrument B is more accurate because it provides readings up to two decimal places, indicating higher precision and smaller least count.

(d) Identify instruments A and B.

Instrument A is a metre scale, while instrument B is a Vernier calipers, which is more precise.

(e) Why are SI units used?

SI units are used to maintain uniformity and standardization in measurements across the world, ensuring consistency and ease of communication in science.

Case Study 2 (Simple Pendulum)
A student recorded time for 20 oscillations for different lengths.

Length (m)	Time (s)
0.40	25.4
0.60	31.0
0.90	38.0
1.00	40.2

(a) Calculate time period.

Time period (T) is calculated using T = time / number of oscillations. Thus, T = t/20. For 0.40 m → 25.4/20 = 1.27 s For 0.60 m → 31.0/20 = 1.55 s For 0.90 m → 38.0/20 = 1.90 s For 1.00 m → 40.2/20 = 2.01 s

(b) Which graph should be plotted?

A graph between the square of time period (T²) and length (L) should be plotted to study the relationship between them.

(c) What conclusion can be drawn?

The graph shows that T² is directly proportional to L, which confirms the relation for a simple pendulum.

(d) What can be calculated from the slope of the graph?

The slope of the graph can be used to calculate the acceleration due to gravity (g).

(e) Will the graph remain same on the Moon?

No, the graph will not remain the same because the value of g on the Moon is smaller. This changes the slope of the graph.