General Physics

GENERAL PHYSICS

1. Physical Quantities and SI Units

A physical quantity is something that can be measured and expressed using a numerical value and a unit.

The main SI quantities in these notes are:

• Length — metre (m)
• Mass — kilogram (kg)
• Time — second (s)

2. Measurement of Length

Length can be measured using different instruments depending on the size of the object. Common instruments include:

• Measuring tape — long lengths
• Metre rule — medium lengths
• Vernier callipers — short and internal/external dimensions
• Micrometer screw gauge — very small dimensions
• Accuracy refers to the smallest measurement that can be read using an instrument.
• An instrument with a smaller scale division can give more precise measurements.

3. Rulers and Measuring Tapes

The eye should be placed directly above the measurement mark when reading a ruler. This prevents parallax error, which occurs when the scale is viewed from an angle.

4. Vernier Callipers

Vernier callipers contain a main scale and a vernier scale. Inside jaws measure internal dimensions. Outside jaws measure external dimensions.

To read a vernier calliper:

1. Read the main scale just before the vernier zero.
2. Find the vernier division that coincides with a main-scale division.
3. Multiply the coinciding division by the least count.
4. Add the main-scale and vernier readings.

Formula: Final reading = Main scale reading + Vernier reading.

5. Micrometer Screw Gauge

A micrometer screw gauge measures very small dimensions, such as the diameter of a thin wire. Important parts include the anvil, spindle, sleeve, thimble, ratchet, and frame. It has a main scale on the sleeve and a circular scale on the thimble. Each circular-scale division may represent 0.01 mm.

To read it:

1. Read the visible main-scale measurement.
2. Read the circular-scale division.
3. Multiply the circular reading by the least count.
4. Add the two readings.

Formula: Final reading = Main scale reading + Circular scale reading.

6. Errors in Length Measurement

Calibration error occurs when an instrument's scale is incorrectly marked. Zero error occurs when an instrument does not read zero when it should. Human error occurs when the user incorrectly reads or interprets the scale.

7. Measurement of Time

Time can be measured using a clock, stopwatch, or pendulum. A stopwatch can measure minutes, seconds, and fractions of a second. Manual stopwatch measurements can be affected by human reaction time.

8. Simple Pendulum

A simple pendulum consists of a bob attached to an inextensible string. Important terms include bob, length, equilibrium position, and oscillation. One complete oscillation is a movement from one extreme position to the other and back to the starting position.

9. Period of a Pendulum

The period (T) is the time taken for one complete oscillation. Formula: T = Total time ÷ Number of oscillations The SI unit of period is the second (s).

10. Frequency of a Pendulum

Frequency (f) is the number of complete oscillations made per second.

• Formula:

f = Number of oscillations ÷ Total time

• The SI unit of frequency is the hertz (Hz).
• One hertz means one oscillation per second.

11. Relationship Between Period and Frequency

• Period and frequency are inversely related.
• T = 1/f
• f = 1/T
• A higher frequency means a shorter period, while a lower frequency means a longer period.

12. Factors Affecting the Period of a Pendulum

The period depends mainly on:

• Length of the pendulum (l)
• Acceleration due to gravity (g)

For small oscillations: T = 2π√(l/g)

• Increasing the length increases the period.
• Increasing gravitational acceleration decreases the period.