PHYSICS [2 Mark Question Answer]

A simple pendulum is a heavy point mass (known as bob) suspended from a rigid support by a massless and inextensible string.
No, the pendulum used in pendulum clock is not a simple pendulum because the simple pendulum is an ideal case. We cannot have a heavy mass having the size of a point and string having no mass.

A pendulum with the time period of oscillation equal to two seconds is known as a seconds pendulum.
OR
“A pendulum which has a time period of two seconds is called seconds’ pendulum”

Pendulum A will take more time (twice) in a given time because the time period of oscillation is directly proportional to the square root of the length of the pendulum. Therefore, the pendulum B will have a greater time period and thus making lesser oscillations.

The ratio of their time periods would be 1:1 because the time period does not depend on the weight of the bob.

A vernier Callipers are said to be free from zero error if the zero marks of the vernier scale coincides with the zero marks of the main scale.

Vernier constant is equal to the difference between the values of one main scale division and one vernier scale division. It is the least count of vernier callipers.

Thickness of the pencil (observed reading) = 1.4 mm
Zero error = + 0.02 cm = + 0.2 mm
Correct reading = observed reading - zero error (with sign)
= 1.4 mm - 0.2 mm
= 1.2 mm

The least count of a metre rule is 1 cm.
The length cannot be expressed as 2.60 cm because a metre scale measures length correctly only up to one decimal place of a centimeter.

Value of 1 m.s.d. = 1 mm
10 vernier divisions = 9 m.s.d.
L.C. = Value of 1 m.s.d./number of divisions on vernier scale
= 1 mm/10
= 0.1 mm or 0.01 cm

The least count of an instrument is the smallest measurement that can be taken accurately with it. For example, if an ammeter has 5 divisions between the marks 0 and 1A, then its least count is 1/5 = 0.2 A or it can measure current up to the value 0.2 accurately.

Pitch of the screw gauge = 0.5 mm
L.C. of the screw gauge = 0.001 mm
No. of divisions on circular scale = Pitch / L.C.
= 0.5 / 0.001
= 500

The least count of a screw gauge can be decreased by

1. Decreasing the pitch and
2. Increasing the total number of divisions on the circular scale.

Least count (L.C.) of a screw gauge : The L.C. of a screw gauge is the distance moved by it in rotating the circular scale by one division.
Thus, L.C. = Pitch of the screw gauge/total no. of divisions on its circular scale.
If a screw moves by 1 mm in one rotation and it has 100 divisions on its circular scale, then pitch of screw = 1 mm.
Thus, L.C. = 1 mm / 100 = 0.01 mm = 0.001 cm

No. of divisions on the circular scale = 50
(i) Pitch = Distance moved ahead in one revolution
= 1 mm/2 = 0.5 mm
(ii) L.C. = Pitch/No. of divisions on the circular head
= (0.5/50) mm
= 0.01 mm

Three uses of vernier callipers are
(a) Measuring the internal diameter of a tube or a cylinder.
(b) Measuring the length of an object.
(c) Measuring the depth of a beaker or a bottle.

A fundamental (or basic) unit is that which is independent of any other unit or which can neither be changed nor can be related to any other fundamental unit.

The three requirements for selecting a unit of a physical quantity are
(1) It should be possible to define the unit without ambiguity.
(2) The unit should be reproducible.
(3) The value of units should not change with space and time.

One lunar month is the time in which the moon completes one revolution around the earth. A lunar month is made of nearly 4 weeks.

The units quintal and metric tonne are two units of mass bigger than the kilogramme.
1 quintal = 100 kg
1 metric tonne = 1000 kg

S.I. unit of mass is ‘kilogramme’.
In 1889, one kilogramme was defined as the mass of a cylindrical piece of a platinum-iridium alloy kept at the International Bureau of Weights and Measures at serves near Paris.