Page 77 - Physics - XI

Q7. How does the least count of the metre scale limit the accuracy in the measurement of mass?
(NCERT)
Ans. Since, a meter scale can measure accurately up to one tenth part of length 1 cm, its least measurement
0.1 cm is called least count of the scale. There is a limitation of meter scale that it cannot measure the
value less than 0.1 cm. So, due to this reason, the least count of the meter scale limits the accuracy
in the measurement of mass.

Q8. What is the resultant torque on the meter scale, due to the gravitational force, when the scale
is perfectly horizontal? (NCERT)
Ans. When the scale is perfectly horizontal, then due to the gravitational force, the torque on the meter
scale will be zero.

Q9. Explain how a physical balance works on the principle of moments?
Ans. A physical balance is a device that is used to measure mass. The physical balance consists of two
pans of equal weights balanced by a beam and the known weight is added on one side while the
unknown weight to be measured is added on the other.

Q10. What is the name given to the point on the scale at which it is balanced horizontally on the
wedge? (NCERT)
Ans. Centre of gravity is a point on the meter scale at which it is balanced horizontally on the wedge.

Q11. What problems would air currents cause in this activity? (NCERT)
Ans. Air currents can be caused by diff erences in temperature, pressure, or impurity concentration. So, the
temperature diff erences can cause air currents because the warmer air is less dense than cooler air,
causing the warmer air to appear lighter. So, ultimately it results into an error in the measurement.

ACTIVITY - 3

Aim

To plot a graph for a given set of data, with proper choice of scales and error bars.

Apparatus and Materials Required
A ruler, an eraser, a sharp pencil, millimetre square graph paper, and given data

Set of Data

Load (gf) 100 200 300 400 500 600
Extension (cm) 0.16 0.32 0.48 0.64 0.82 0.98

Principle/Theory

Graph: It is a curve which shows the variation of two variable quantities of which one changes as a result
of change in the other.
Error Bar: When the value of variable is not represented on the graph by a point only, then it can be
represented by a bar called error bar around the point. The width of the bar is equal to the least count of
the measuring instrument.

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