Experimental Skills Summary

Measuring Instruments, Physics Experiments, and Electronics

Measuring Instruments
Mechanics Experiments
Waves & Sound
Electricity
Optics
Electronics

1. Measuring Instruments for Length

(A) Instruments with Linear Scale

Metre Scale

Basic measuring instrument with least count typically 1 mm.

Vernier Calipers

Used for more precise measurements than a metre scale.

Vernier Constant = 1 MSD - 1 VSD
Travelling Microscope

Used for very precise linear measurements with vernier scale.

(B) Instruments with Circular Scale

Screw Gauge

Used for measuring small dimensions like wire diameter.

Least Count = Pitch / Number of divisions on circular scale
Spherometer

Used to measure radius of curvature of spherical surfaces.

Same least count formula as screw gauge

Key Points:

  • Vernier Constant (Least Count) is the smallest measurement that can be taken with the instrument.
  • Pitch is the linear distance moved on the main scale in one complete rotation of the circular scale.
  • For accurate measurements, always check for zero error and apply correction if necessary.

2. Mechanics Experiments

2.1 Simple Pendulum

In absence of energy loss, the amplitude of oscillations remains constant and the time period is given by:

\[T = 2\pi \sqrt{\frac{L}{g}}\]
Total Energy = \(\frac{1}{2} m \omega^2 A^2\)

With damping, amplitude decreases exponentially.

2.2 Young's Modulus

Measured using Searle's apparatus with two wires:

  • Experimental wire - material under test
  • Auxiliary wire - used for comparison

Important:

Both wires should initially be of same length and same material for accurate comparison.

2.3 Surface Tension

Determined by capillary rise method:

\[\sigma = \frac{h r \rho g}{2 \cos \theta}\]

Where: σ = surface tension, h = capillary rise, r = radius of capillary, ρ = density, θ = contact angle

2.4 Viscosity

Measured using Stokes' law with spherical object falling in liquid:

\[\eta = \frac{2r^2 (\rho - \sigma) g}{9v_t}\]

Where: η = viscosity, r = radius of sphere, ρ = density of solid, σ = density of liquid, vₜ = terminal velocity

2.5 Specific Heat

Measured using:

  • Cooling curve method - based on Newton's law of cooling
  • Method of mixtures - based on principle of calorimetry
Newton's Law: \(\frac{d\theta}{dt} \propto (\theta - \theta_0)\)

3. Waves and Sound Experiments

3.1 Resonance Tube

Used to determine speed of sound in air at room temperature.

For first and second resonance with tuning fork of frequency ν:

\[C = \nu \times 2(\ell_2 - \ell_1)\]

Where: C = speed of sound, ℓ₁ = length for first resonance, ℓ₂ = length for second resonance

Procedure:

  1. Find air column lengths for first and second resonance with same tuning fork
  2. Calculate the difference between these lengths
  3. Multiply by 2 and by the frequency to get speed of sound

4. Electricity Experiments

4.1 Resistance Measurement

Methods to measure resistance:

  • Ohm's Law - Using voltmeter and ammeter
  • Post Office Box - Based on Wheatstone bridge principle
  • Metre Bridge - Based on Wheatstone bridge principle

Important Connections:

  • Voltmeter always connected in parallel
  • Ammeter always connected in series
  • In Metre Bridge, interchange resistances to eliminate end corrections

4.2 Potentiometer

Works on principle that when current flows through uniform wire, potential difference between two points is directly proportional to length between them.

Uses of Potentiometer:

  1. Compare EMF of two cells
  2. Compare two resistances
  3. Measure internal resistance of a cell

Important Condition:

EMF of driving cell (in main circuit) should be greater than that of cells in auxiliary circuits.

5. Optics Experiments

5.1 Focal Length Measurement

Using optical bench for:

  • Concave mirror
  • Convex mirror
  • Convex lens

For Concave Mirror & Convex Lens:

  • Real image formation possible
  • Can use parallax method
  • Can calculate graphically using u-v method

For Convex Mirror:

  • Always forms virtual image
  • Need convex lens to form real image

5.2 Refractive Index Measurement

Glass Slab Method:

Using concept of real depth and apparent depth:

\[\mu = \frac{\text{Real depth}}{\text{Apparent depth}}\]

Prism Method:

Using minimum deviation method:

\[\mu = \frac{\sin\left(\frac{A + D_m}{2}\right)}{\sin\left(\frac{A}{2}\right)}\]

Where: A = angle of prism, Dₘ = minimum deviation

6. Electronics Experiments

6.1 Diodes

For diode to conduct: Anode should be positive with respect to cathode.

Regular Diode:

  • Conducts in forward bias
  • Blocks in reverse bias

Zener Diode:

  • Used in reverse biased condition
  • Used as voltage regulator

6.2 Transistors

For proper working:

  • Base-Emitter (b-e) junction: Forward biased
  • Base-Collector (b-c) junction: Reverse biased

Characteristics studied:

  1. Input characteristics
  2. Output characteristics
  3. Mutual or transfer characteristics

6.3 Multimeter Usage

Used to identify components:

Diode Identification:

  • Very low resistance in one direction (forward bias)
  • Very high resistance in opposite direction (reverse bias)

Transistor Identification:

  • Three-terminal device
  • If conduction occurs between emitter-base and base-collector in both cases
  • The common terminal is the base

Resistor Identification:

  • Same resistance in both directions