Measuring Wavelength of Light with Laser Diffraction Grating

Experiment 6: Measuring the Wavelength of Light using Laser Diffraction Grating

• Purpose: To measure the wavelength of a HeNe laser using a diffraction grating
• Apparatus:
  • Scale (100 cm)
  • Laser source (HeNe)
  • Holders
  • Screen
  • Mounted pin (Object)
  • Diffraction Grating (100-600 lines per millimeter)
• Theory:
  • A diffraction grating consists of a large number of equally spaced parallel slits
  • The space between any two lines is transparent to light and acts as a separate slit
  • The grating has three windows per slide (100, 300, and 600 lines per millimeter)
  • The geometry of light after passing through the diffraction grating is shown in Figure 1
  • The angle θ denotes the second maxima, and there is a θn for each xn

Experiment 5: Ohm's Law

• Aim: To investigate Ohm's Law
• Apparatus:
  • Power supply "E"
  • Ammeter
  • Rheostat
  • Constant resistance "R"
  • Voltmeter
• Theory:
  • Electrical resistance opposes the passage of electric current
  • The symbol R denotes the electrical resistance of the tungsten filament in the light bulb
  • Ohm's Law states that the current in a conductor is directly proportional to the potential difference and inversely proportional to the resistance of the conductor
  • The relationship between V and I is represented in Figure 3

Experiment 3: Lenses

• Objective: To find the focal length of a convex lens using two methods
• A. Focal Length Converging Lens (Displacement Method)
• Theory:
  • A lens is a piece of glass or other transparent material shaped to produce an image by refracting light
  • Lenses are used in many purposes (eye glasses, cameras, telescopes, microscopes, and even in our eyes)
  • Convex lenses are converging lenses, while concave lenses are diverging lenses

Experiment 2: Viscosity of Liquid

• Purpose: To determine the viscosity of a medium using a small sphere falls with a constant terminal velocity
• Apparatus:
  • Long glass tube (50 cm long)
  • Glycerin
  • Meter Scale
  • Small Sphere
  • Rubber bands
  • Magnet
  • Stop Watch
• Theoretical background:
  • A body moving in a fluid feels a frictional force in a direction opposite to its direction of motion
  • The dynamic viscosity η measures the internal friction of the fluid
  • Stokes derived an expression for the frictional force on a sphere moving in a fluid

Experiment 1: Surface Tension

• Objective: To measure the surface tension of a liquid
• Medical Application:
  • The alveoli in the lungs are similar to interconnected bubbles
  • The surface tension of the liquid lining the alveoli is an important factor in the pressure-volume relationship of the lung
  • Pulmonary surfactant lowers the surface tension by getting between water molecules, reducing their ability to attract each other by hydrogen bonding
  • The absence of surfactant in the lungs of some newborn infants, especially premature, is the cause of Respiratory Distress Syndrome (RDS)

General Properties of Sound

• A sound wave is a pattern of disturbance caused by energy traveling away from the source of sound.
• Sound is a mechanical disturbance that propagates through an elastic material medium with a definite velocity.
• In air, sound can be defined as a local increase (compression) or decrease (rarefaction) of pressure relative to atmospheric pressure.

Sonic Spectrum

• Sonic spectrum can be classified into three frequency ranges: infrasound, audible sound, and ultrasound.
• The human ear can hear sounds in the range of roughly 20 Hz to 20 KHz.
• Infrasound refers to sound frequencies below 20 Hz, produced by natural phenomena like earthquake waves and atmospheric pressure changes.
• Infrasound can travel long distances without losing much power, and its effects can be difficult to minimize.
• Infrasound can produce clear symptoms including respiratory impairment, aural pain, fear, visual hallucinations, and chills.
• Infrasound can also be used to study heart mechanical function, revealed by the seismocardiogram.
• Ultrasound is the frequency range above 20 KHz, used clinically in various specialties.

Effect of Sound on Human Hearing

• The human ear can distinguish two characteristics of sound: loudness (or volume) and pitch.
• Loudness is the degree of sensation of sound produced in the ear, dependent on its intensity.
• Pitch refers to whether a sound is high (sharp) or low.

Sound Reflection and Transmission

• When a sound wave is applied perpendicularly to the interface between two media with different acoustic impedance, a portion of the wave will pass through and another will reflect.
• The ratio of reflected (or transmitted) and incident waves can be measured.
• If the acoustic impedance of the two media is equal, there is no reflected wave, and transmission to the second medium is complete.
• If the acoustic impedance of the two media is different, the sign change indicates a phase change of the reflected wave.

Applications of Sound in Medicine

• Stethoscopes are diagnostic instruments that amplify sounds made by the body from the heart, lungs, or other body sites.
• The bell of a stethoscope serves as an impedance matcher between the body and the air in the tube.
• The frequency of the sounds must resonate in the bell membrane, and the natural frequency of the bell depends on its size and diaphragm tension.
• Stethoscopes can be used to selectivity pick up certain frequency ranges (e.g., low-frequency heart murmurs, high-frequency lung sounds).

Properties of Sound Waves

• The speed of sound is given by the formula: c = √(T/ρ)
• The frequency of a sound wave is denoted by the formula: f = 1/T
• The wavelength of a sound wave is denoted by the formula: λ = c/f
• The intensity of a sound wave is the energy carried by the wave per unit area and per unit time, expressed by the maximum change in pressure.

Sound Intensity Level [Ratio]

• The intensity of a sound wave can be compared to a reference intensity using the formula: Intensity ratio = I / I0
• The absolute value of sound intensity cannot be measured directly.