PHYSICS [5 Mark Question Answer]

To measure the mass of a body using a physical balance
(i). Before starting, bring the plumb line just above the pointed projection by adjusting the leveling screws at the base. The beam is then gently raised using the lever. And it should be ensured that the pointer swings equally on both sides of the zero mark of the scale.
(ii). Now lower the beam gently and the given body is kept on the left pan.
(iii). Next, place some weight on the right pan form the weight box using the forceps.
(iv). Now the lever is turned towards the right so that the beam rises and the power begins to swing to pointer swing on either side. It must be carefully noted that the side to which the pointer moves more, denotes lesser mass on that side.
(v). Go on adjusting the standard weights till the pointer swings equally on both sides of the zero mark.
(vi). At this stage, the total mass of weights on the right pan gives the mass of the body.

Table to record the time period of a simple pendulum for different effective lengths.

Effective length, L (m)	Time period, T (s)
L1	T1
L2	T2
L3	T3
L4	T4
L5	TS

The presentation of the data in a tabular form helps in quickly grasping and analyzing the recorded observations. For example, to measure a diameter using a vernier caliper we record the following data in a tabular form as follows

Vernier caliper

No. of observations	Main scale reading (cm)	No. of vernier divisions p coinciding with main scale	Vernier reading =L.C. X p (cm)	Observed diameter
1
2
3

The measurements corresponding to one physical quantity from one instrument must be recorded in one table. And the name of the instrument should be written on top. Observation must be recorded up to the limit of the instrument and form the recorded individual observations, calculate the mean value, and record it at the bottom of the column.

For measuring the length of an object using a vernier caliper, these steps are followed:-
(a). First of all, we find the least count and zero error of the vernier calipers.
(b). Place the object whose length is to be measured below the lower jaws and move the jaw till it touches the object. Record the main reading.
(c). Note the division on the vernier scale that coincides with some division of the main scale. Multiply this number of vernier division with least count. This is vernier scale reading.
(d). Record the observed length by adding the main scale reading and the vernier scale reading. Also, subtract zero error with its proper sign, if any, from the observed length to find the true length of the object.

Rules observed while writing unit of a physical quantity :

1. It must be of proper size. A very small or large size may cause inconvenience.
2. It should be easily accessible
3. It must be reproducible at all places without any difficulty.
4. It must be accurately defined and must not change with time, place, and physical conditions such as pressure, humidity, etc.
5. It must be widely accepted all over the world.

Fundamental units in a SI system

Quantity	Unit	Symbol
Length	Metre	M
Mass	Kilogram	Kg
Time	Second	S
Temperature	Kelvin	K
Luminous intensity	Candela	Cd
Electric current	Ampere	A
Amount of substance	Mole	Mol

(a) Measuring the diameter of the rod



(b) Measuring Internal diameter of a cavity


(c) Measuring the depth of a cavity Least count of vernier caliper = 0.01 cm

(i) Main scale reading = 5.5 cm
Vernier scale division coinciding with main scale = 6 Vernier scale reading = 6 × 0.01 cm = 0.06 cm
Diameter of rod = 5.5 + 0.06 = 5.56 cm

(ii) Main scale reading = 1.6 cm
Vernier scale division coinciding with main scale = 5
Vernier scale reading = 5 × 0.01 cm = 0.05 cm
Internal diameter of a cavity = 1.6 + 0.05 = 1.65 cm

(iii) Main scale reading = 3.1 cm
Vernier scale division coinciding with main scale = 5 Vernier scale reading = 5 × 0.01 cm = 0.05 cm
Depth of a cavity = 3.1 + 0.05 = 3.15 cm

The main characteristics of a standard unit are as follows
(a). It must be well defined.
(b). It must be of proper size. A very small or large size may cause inconvenience.
(c). It should be easily accessible
(d). It must be reproducible at all places without any difficulty.
(e). It must be accurately defined and must not change with time, place, and physical conditions such as pressure, humidity, etc.
(f). It must be widely accepted all over the world.

Fundamental units of the SI system are

Quantity	Unit	Symbol
Length	Metre	M
Mass	Kilogram	Kg
Time	Second	S
Temperature	Kelvin	K
Luminous intensity	Candela	Cd
Electric current	Ampere	A
Amount of substance	Mole	Mol

An ideal pendulum is a simple pendulum consists a heavy mass (called the bob) considered as a point mass suspended by a thread which is considered to be massless and inextensible or non-elastic, from a fixed point or rigid support and in which there is no friction between the support and the string.

Graph of T versus l for a simple pendulum

The presentation of the data in a tabular form helps in quickly grasping and analyzing the recorded observations. For example, to measure a diameter using a vernier caliper we record the following data in a tabular form as follows
Vernier caliper

No. of observations	Main scale reading (cm)	No. of vernier divisions p coinciding with main scale	Vernier reading =L.C. X p (cm)	Observed diameter
1
2
3

The measurements corresponding to one physical quantity from one instrument must be recorded in one table. And the name of the instrument should be written on top. Observation must be recorded up to the limit of the instrument and form the recorded individual observations, calculate the mean value, and record it at the bottom of the column.

Precautions to be taken to measure the mass of a body using beam balance are
(a). The beam must be gently lowered before adding or removing weights from the pan.
(b). The weights should not be carried with bare hands to avoid the change in weights due to moisture and dust particles from the surrounding.
(c). The lever should be turned gently, in order to prevent knife-edges from chipping.
(d). Never keep the wet or hot objects on the pan.
(e). The weights should be placed into the weight box after use.
(f). Whenever you are near the actual weight, you should carefully try the weights in the descending order.

Due to mechanical errors, sometimes when the anvil and spindle end are brought in contact, the zero mark of the circular scale does not coincide with the base line of main scale. It is either above or below the base line of the main scale, in which case the screw gauge is said to have a zero error. It can be both positive and negative.
It is accounted by subtracting the zero error (with sign) from the observed reading in order to get the correct reading.
Correct reading = Observed reading - zero error (with sign)

A well-labeled diagram of Vernier caliper is shown in figure

The following procedure is used to measure the diameter of a wire
(a). Calculate the least count and zero error of the screw gauge.
(b). Place the wire in between the studs. Turn the ratchet clockwise so as to hold the wire gently in between the studs. Record the main scale reading.
(c). Now record the division of circular scale that coincides with the base line of the main scale. This circular scale division multiplied by the least count will give circular scale reading.
(d). The observed diameter is obtained by adding the circular scale reading to the main scale reading. Subtract the zero error if any, with its proper sign, from the observed diameter to get the true diameter.

Fundamental units in SI system.

Quantity	Unit	Symbol
Length	Metre	M
Mass	kilogram	kg
Time	Second	S
Temperature	Kelvin	K
Lumibous Intensity	Candela	Cd
Electric Current	Ampere	A
Amount of substance	Mole	Mol
Angle	Radian	Rad
Solid Angle	Steradian	sr

A simple pendulum consists of a heavy point mass (called the bob) suspended by a massless and an inextensible or non-elastic thread from a fixed point or rigid support.