Notes, summaries, assignments, exams, and problems for Physics

Photomultiplier Characteristics

What is dark current?

The dark current is a small amount of current flowing in the photomultiplier even when it is not illuminated. This current should be minimized for accurate measurements. The region between 800 V and 1300 V is often ideal for operating the photomultiplier.

The primary source of dark current is the thermionic emission rate from the photocathode and dynodes. Other sources include:

• Leakage current
• Incandescent lighting phenomena
• Field emission
• Current from residual gas ionization
• Radioactive contamination within the device materials

What is the photomultiplier gain?

The gain (G) of a photomultiplier is the ratio between the number of electrons at the output and the number of photons incident on the photocathode.... Continue reading "Photomultiplier Dark Current, Gain & Lifetime Measurements" »

Archimedes' Principle

Archimedes' Principle: Any body immersed in a fluid suffers an apparent weight loss equal to the weight of the liquid displaced (evicted).

Pressure Concepts

Pressure: It is the force exerted per unit area.

Atmospheric Pressure: Pressure exerted by the atmospheric layer above the Earth.

Hydrostatic Pressure: Is the pressure exerted by a column of fluid at the bottom of the tank that contains it.

Pascal's Principle

Pascal's Principle: All fluid enclosed in a tank, when subjected to pressure, exerts this in all directions with equal intensity.

Flow Characteristics

• Steady-flow: When the particles of a fluid passing a given point of the pipe keep the speed constant.
• Incompressible-flow: Liquids are considered incompressible because their

Concept of Slope and Gradient

The closeness of curves indicates a steep slope, while a large separation indicates a slight incline. This equidistance, whenever we have to compare the two cases, is the same. The equidistance of curves in a plane is unique.

• A series of concentric curves, where the heights rise to the center, indicates a rise or hill.
• A series of concentric curves, in which the dimensions decrease toward the center, indicates a depression or hollow.

We define slope as the ratio between the horizontal and vertical displacement, always looking from the top down. The gradient is defined as the ratio between the vertical and horizontal displacement.

Alignment

• Natural Distance (Dn): Dn is the distance traveled on the ground, following the

**Fe, Co, Ni: Ferromagnetic Materials**

_Iron (Fe), Cobalt (Co), and Nickel (Ni)_ are ferromagnetic materials. They strongly attract metals and exert attractive or repulsive forces on other materials.

**Early Discoveries in Magnetism**

• **William Gilbert:** Identified North and South Poles as magnetic.
• **First Discovered Natural Magnet:** Magnetite (iron oxide (Fe₃O₄)) and Magnesia (Chinese).

**Electric and Magnetic Fields**

• **Charge (Q) at rest:** Creates an electric field.
• **Moving charge:** Creates an electromagnetic field.

Analogy:

• Computer storage ↔ Electric field
• Mass ↔ Gravitational field
• Magnet ↔ Magnetic field

**Key Figures in Electromagnetism**

• **1831 Michael Faraday:**

  Introduced the concept of lines of force to explain the behavior of forces

Motor Performance Problem

A motor has a resistance of 250 Ω and operates at 100 V at 25 °C. The temperature coefficient of resistance (α) at 25 °C is 0.0018 /°C. We need to determine the following:

Questions for Analysis

1. The resistance value when the temperature is 50 °C.
2. The current absorbed from the network when the temperature is 25 °C and 50 °C.
3. The cost of the energy consumed in 120 minutes at 50 °C if the cost per kWh is $1.
4. At what temperature and why does the motor consume less energy?

Principles of Electromagnetism

Induced Electromotive Force (EMF)

When a conductor of length (l) moves with a constant velocity (v) within a magnetic field of induction (B), an electromotive force (EMF) is induced across its ends.

• Perpendicular Motion:

Vacuum and Pressure Measurement Devices

Cold Cathode Ionization Transducer

The cold cathode transducer is based on the principle of measuring the ion current produced by a high-voltage discharge. Electrons detached from the cathode take a spiraling motion as they move through a magnetic field on their way to the anode. This spiraling motion ensures that the mean free path of the electrons is greater than the distance between the electrodes.

This extended path increases the possibility of collisions with residual gas molecules, leading to increased ion current. Consequently, the cathode discharge is maintained at a lower pressure, indicating a higher vacuum level. While this instrument cannot degas as quickly as a hot filament gauge, it is significantly... Continue reading "Vacuum Transducers and Pressure Control Mechanisms" »

Work-Energy Theorem

The work (Wt) done by the net force on an object is equal to the variation in its kinetic energy (ΔEc). This can be expressed as: Wt = ΔEc = Ec2 - Ec1, where Ec1 is the initial kinetic energy and Ec2 is the final kinetic energy.

Gravitational Potential Energy

Gravitational potential energy is the energy associated with a system of two masses attracted by a gravitational force. It is also defined as the work required to move a mass 'm' from infinity to a specific distance 'r' from the Earth.

Variation of Potential Energy

The variation of potential energy is the work required to move a mass 'm' from a first point to a second point within a force field.

Moment of a Force (Torque)

The moment of a force (F) represents the ability... Continue reading "Fundamental Concepts in Mechanics and Gravitation" »

Item 18. Non-ionizing Radiation

Non-ionizing radiation is radiation that is not capable of producing ions when interacting with atoms of a material. It is characterized by low frequency and small photon energy (<1.23 meV).

Main Types

They fall into two main groups:

• Microwave (MW) and radio frequency (RF)
• Visible and near

Public Health Concern

In May 1996, in response to growing concern in many Member States about the potential public health effects of exposure to electric and magnetic fields emitted by increasingly numerous and diverse sources, the World Health Organization launched an international project to assess the health and environmental effects of exposure to these fields. This became known as the International EMF Project.

Units

• Electric

Ancient Worldviews

Worldview: The Greek "cosmos" implied a beautiful order and harmony, as opposed to chaos and disorder. It represents a coherent and systematic view of the world, a total interpretation of reality.

Scientific Worldviews

Theories of science:

• Astronomy: Studies the stars.
• Cosmology: A part of astronomy that explains the origin and evolution of the universe.
• Physics: A fundamental science for understanding the world, contributing laws that explain the movements and forces affecting bodies.

Former Worldviews: 6th Century BC

• Principles of Reality

  The ancients believed that all substances came from the transformation of one or several elements that could be considered the origin of reality.

  • Basic Principle or Arche

    The Milesian school of philosophy

Acoustics Fundamentals

Acoustics is the part of physics that deals with the study of sound from sound waves.

Sound Waves

Are those that produce sound.

Mechanical Waves

These are waves that produce due to a disturbance, and their propagation in the form of oscillation requires a material medium.

Classification of Mechanical Waves

This classification agrees with the direction in which a wave vibrates the particles of the material medium.

Longitudinal Waves

They occur when material particles of the medium vibrate parallel to the direction of wave propagation.

Transverse Waves

They occur when material particles of the medium vibrate perpendicular to the direction of wave propagation.

Sound Definition

A longitudinal mechanical wave that propagates through an... Continue reading "Physics of Sound: Waves, Frequencies, and Intensity" »