PHYSICS [3 Mark Question Answer]

Three 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). Whenever you are near the actual weight, you should carefully try the weights in the descending order.

In order to measure the length of an object using a metre rule, the metre rule must be placed with its marking close to the object, such that the zero marking on the scale coincides with one end of the object. Then the reading on the scale corresponding to the other end of the object will give the length of the object. Precautions to be taken for measuring the length of the object, the eye must be kept vertically above the end of the object to avoid parallax and the corresponding marking along the line should be carefully read. The meter scale can measure up to an accuracy of 1mm or 0.1 cm

No, we cannot measure the diameter of a wire by wrapping it around a pencil because it is not very accurate. We can use a screw gauge for this purpose as it can measure the diameter correct up to 1/100 of a millimeter or even less.

If the zero of the circular scale does not coincide with the zero of the main scale (pitch scale) when the end of the movable screw is brought in contact with the fixed end then the screw gauge is said to have a zero error.

Here, zero of the vernier scale coincides with the zero of the main scale, So, the zero error and zero error correction is nil.

The maintenance of standard units is essential because any variation in these standards would lead to wrong measurements, misleading results, and confusing generalizations. The standards are preserved in such a way that they do not undergo any change with the change in temperature, pressure, humidity, and other environmental changes.

Difference between fundamental units and derived units.

Fundamental units	Derived units
These units are not derived from other units	These units are derived from fundamental units
These cannot be further resolved into smaller units	These can be resolved into fundamental units
Fundamental units of mass, length, time are kilogram, metre, second respectively	Derived units are speed, density, etc

Measurement is needed for a precise description of any phenomenon happening in the world. For example, if a body is freely falling down to the ground, to understand this phenomenon we must know its velocity, time it will take to reach the ground, etc, and to get answers to all our questions we need a measurement.

A physical balance works on the principle of moments. According to the principle of moments, under equilibrium condition, the clockwise moment due to the body on one side of the beam equals the anti-clockwise moment due to standard weights on the other side of the beam. 

Due to constant use, there is space for the play of screw gauge but gradually this space increases with the use or wear and tear so that when the screw is moved by rotating it in some direction, it slips in the nut and does not cover any linear distance for some rotation of the screw head. The error due to this is known as backlash error. It is avoided by turning the screw always in the same direction.

If the zero of the circular scale lies above the line of graduation then it is called negative zero error. When there is a negative zero error, then the instrument reads less than the actual reading. Therefore in order to get the correct reading, the zero error should always be added from the observed reading.

When one complete rotation is given to the screw hand, it moves forward or backward by a distance is called the pitch of the screw. It is a distance between two consecutive threads of the screw.
Pitch of the screw = distance traveled by screw-in n rotations/n rotations

If the zero of the one scale (vernier scale or circular scale of screw gauge) does not coincide with the zero of the main scale, this is known as zero scales, zero error arises. There are two types of zero error -
(a) If the zero of the scale remains below the line of graduation of the main scale then it is called positive zero error
(b) If the zero of the scale lies above the line of graduation of the main scale then it is called negative zero error

Least count of an instrument refers to the smallest reading that can be accurately measured while using the instrument. For an instrument provided with a scale, the least count is the value of one division on its scale.

Basically there is no difference between the quantity being measured but there is a difference of significant figures in the measurement.
(a). Number of significant figures = 3
(b). Number of significant figures = 4
(c). Number of significant figures = 5
Since (c) part has the maximum number of significant figures = 5, therefore it is most accurate among the given three.

Two types of errors in measurement are
(a). Random errors-these errors are due to various factors. In a number of observations, we get different readings every time.
These errors can be minimized by making observations a large number of times and taking the arithmetic mean of the readings.
(b). Gross error- these errors are due to the carelessness of the observer like parallax, improper setting of the instrument.
These errors can be minimized only when the observer is careful in setting up of instrument and taking readings.

Accuracy is the extent to which a reported measurement approaches the true value of the quantity measured. This extent is usually described by the least count of the instrument and since the least count for a given instrument is limited hence, the accuracy of the instrument is limited.

The least count of an instrument refers to the smallest reading that can be accurately measured while using the instrument. For an instrument provided with a scale, the least count is the value of one division on its scale.

A beam balance works on the principle of moments. According to the principle of moments, under equilibrium condition, the clockwise moment due to the body on one side of the beam equals the anti-clockwise moment due to standard weights on the other side of the beam.

A graph of I against T2 for a simple pendulum of length I and time period T is shown in the figure

When one complete rotation is given to the screw hand, it moves forward or backward by a distance called the pitch of the screw. It is a distance between two consecutive threads of the screw.
Pitch of the screw = distance travelled by screw-in n rotations/n rotations

Precautions to be taken while measuring the volume of a solid lighter than water using the displacement method
(a). The sinker should be insoluble in water
(b). The sinker should have a high density than water.
(c). Lower meniscus should be read to note down the readings and errors due to parallax should be avoided.

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

If the zero of the circular scale lies above the line of graduation then it is called negative zero error. When there is a negative zero error, then the instrument reads less than the actual reading. Therefore in order to get the correct reading, the zero error should always be added to the observed reading.

When one complete rotation is given to the screw hand, it moves forward or backward by a distance is called the pitch of the screw. It is a distance between two consecutive threads of the screw.
Pitch of the screw = distance travelled by screw-in n rotations/n rotations

Pitch of the screw gauge = 0.5mm = 0.05 cm
Circular scale divisions = 100
Least Count of screw gauge = pitch of the gauge/circular scale divisions
= 0.05/100
= 0.0005cm

If the zero of the circular scale remains below the line of graduation then it is called positive zero error. When there is a positive zero error, then the instrument reads more than the actual reading. Therefore in order to get the correct reading, the zero error should always be subtracted from the observed reading.

Due to constant use, there is space for the play of screw gauge but gradually this space increases with the use or wear and tear so that when the screw is moved by rotating it in some direction, it slips in the nut and does not cover any linear distance for some rotation of the screw head. The error due to this is known as backlash error.