Physics for students

Physical Quantity: Any measurable quantity is called Physical Quantity.

Base Quantity: The physical quantity that could be measured independently is called a base quantity.

I will be removing the phrase .........is called or ........is defined as ...

Derived Quantity: The physical quantity that depends upon other physical quantities for measurement.

Vector: The physical quantity that has both magnitude and direction.

Scalar: The physical quantity that has magnitude only.

Actually, vector means 'to carry' and scalar means 'of a scale', so if we try to learn through etymology we can learn the definitions easily.

Precision: The degree to which the  observed values are least scattered.
The precision is the measure of goodness of data. Many of us may have misconception that precision has to do anything with the errors made by experimenter. During recording of data, we take a large number of data. Precision refers to the spread of data for at least one fixed parameter.

Accuracy: The degree to which the observed value approaches the true value.
The accuracy is based on the type of instrument we use. If a length is measured with a micrometer screw gauze the reading may be 1.738 cm, the same length recorded by vernier calipers is 1.74 cm and for meter rule it is 1.7 cm. Here the degree of accuracy is decreasing. Actually, the least count plays an important role on accuracy of the data.

Systematic Error: The error that arises due to known causes.
As the cause is known one can eliminate the error by proper adjustment of the instrument. Furthermore, if the reading has a error of same magnitude, it is a systematic error.

Random Error: The error that arises due to unknown causes.
As the cause is unknown, it can't be removed; but one can minimize the error by taking multiple readings for a parameter and taking the average value.

In Young's Double Slit experiment following changes are observed if we change the parameters in following way:

DOUBLE SLIT ARRANGEMENT

INTERFERENCE AND FRINGE FORMATION

1. If wavelength of the incident light is increased the fringe spacing will be increased as it is directly proportional to the wavelength of the incident light but the contrast between the bright and dark fringes will not be affected.

2. If the double slit separation is increased the fringe spacing will be reduced as it is inversely proportional to the double slit separation but the contrast between the bright and dark fringes will not be affected.

3. If the distance from the double slits to the screen is increased the fringe spacing will be increased as it is directly proportional to distance between the double slit and screen but the contrast between the bright and dark fringes will be reduced as the intensity of the bright fringes will be reduced.