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

Wave Reflection Study

Purpose

To study the reflection of a plane wave, generated by a wave source, off different obstacles.

Planning

1. Position the right triangle reflector in the form of a right angle.
2. Generate plane waves incident upon the reflector.
3. Affix paper to the table. Use a ruler to draw one or more lines to show the front of the incident wave and the reflected wave front. Ensure the ruler is parallel to the corresponding disturbance.
4. Trace the position of the reflective barrier.
5. Repeat steps for two other positions of the triangle.

Part 2: Reflection in a Curved Obstacle

1. Trace the circular barrier on a new sheet of paper.
2. Mark the position where the reflected waves converge.
3. Turn off the generator. Use your fingertip to produce a circular pulse

Conservative Forces and Inertia

Conservative Force: The work done is independent of the distance traveled and only depends on the changes in potential energy. The work (W) performed by a conservative force comes at the expense of a decrease in potential energy (Ep).

Forces of Inertia: These are forces that enter the mathematical description of moving bodies in an accelerated system so that Newton's laws remain valid. Example: A ball hanging from the roof of a bus.

Kepler's Second Law of Planetary Motion

Kepler's 2nd Law: If t1 = t2, then A1 = A2. This means that planets do not move with the same speed at all points of the orbital path; when they are closer to the Sun, they move faster, and when they are farther away, they move slower.

Electric Field

Key Kinematics Concepts

Reference System

A reference system is a coordinate system (O, X, Y) combined with a clock, used to define the position and motion of objects.

Position

Position is the location of a body in space, defined by coordinates within a chosen reference system.

Trajectory

The trajectory is the imaginary path or line described by a moving body, formed by the sequence of positions it occupies over time.

Distance Traveled (Path Length)

Distance traveled (or path length) is the total length of the path covered by a body along its trajectory.

Displacement

Displacement is the vector difference between a body's final and initial positions, indicating the change in position and direction. It is measured in meters (m).

Velocity

Velocity is a vector... Continue reading "Fundamental Concepts of Motion in 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

Gravitational and Electric Forces Comparison

Similarities and Differences: An Analogy

The mathematical expressions for these forces are similar. Both forces are proportional to the extent of physical interactions, specifically gravitational mass and electric charge. In both laws, forces are inversely proportional to the square of the distance. Furthermore, both are central forces, acting in the direction of the straight line joining the masses or charges.

Key Differences Between Forces

• The gravitational force depends on mass, while the electric force depends on electric charge.
• Gravitational force is strictly attractive, whereas electric force involves both attraction and repulsion.
• The value of the gravitational constant (G) does not depend on the

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: