SCI EXAM 2ND QUARTER

Electromagnetic Waves

Electromagnetic waves are waves that are created as a result of vibrations between an electric field and a magnetic field. These waves can travel through a vacuum (empty space) and do not need a medium to propagate.

Wavelength

Wavelength is the distance measured from one crest of a wave to the next crest or from one trough to the next trough. It is usually measured in meters (m).

Frequency

Frequency refers to the number of waves that pass a given point in a specified amount of time. It is typically measured in Hertz (Hz), where 1 Hz equals one wave per second.

Speed of Light (c)

The speed at which electromagnetic waves travel through a vacuum. It is approximately 3 x 10^8 meters per second (m/s). This is the maximum speed at which any wave can travel.

Radio Waves

Radio waves are electromagnetic waves with the longest wavelengths and the lowest frequencies. They are commonly used for communication, such as in radio, television, and cell phones.

Microwaves

Microwaves are electromagnetic waves with shorter wavelengths than radio waves but longer than infrared waves. They are used in microwave ovens, radar systems, and for communication purposes.

Infrared Radiation

 Infrared radiation has wavelengths shorter than microwaves but longer than visible light. It is primarily associated with heat, as it can be absorbed and emitted by warm objects. Commonly used in night vision and remote controls.

Visible LIGHTs

• Light: It enables us to see things and provides light for electronic device screens.

• Artificial Lights: These are light sources like flashlights and lamps that produce light, unlike natural light from the sun.

• Optical Fibers: A use of optical fibers in medicine is the endoscope, a flexible tube with a tiny camera used to observe the body's internal parts.

Ultraviolet (UV) Radiation

• Vitamin D production: Ultraviolet B (UVB) radiation from sunlight interacts with a protein in the skin (7-DHC) to create vitamin D3, which is important for healthy bones and teeth.

• Security markings: Sensitive documents like credit cards and passports have UV watermarks that are only visible under UV light.

• Water sterilization: UV light disinfection is a water treatment method that eliminates most microbiological contamination.

• Fluorescence: Some laundry detergents contain fluorescent chemicals that glow in sunlight, making clothes appear "whiter than white."

X-rays

• Diagnosing bone fractures: X-rays are produced when fast-moving electrons hit a metal target. Long-wavelength X-rays can penetrate flesh but not bones, which is why they are used to diagnose bone fractures.

• Airport security scanner: Short-wavelength X-rays can penetrate through metals, which is why they are used in airport security scanners.

Gamma Rays

• Radiotherapy: High-energy gamma rays are used to destroy cancer cells in tumors.

• Sterilization: Gamma rays sterilize surgical instruments by penetrating through materials and killing bacteria and other microorganisms.

refraction

It is the change in the direction of light when it passes form one medium to another of different optical density.

It occurs as a result of the change in the speed of light as light crosse the boundary of the two different media.

OPTICAL DENSITY

It is related to the transparency of a material to light.

The higher the optical density of a material, the slower that light travels through it.

INDEX OF REFRACTION

The optical density of a material is indicated by its index of refraction or refractive index, which is the ratio of the speed of light in a vacuum to that in the material.

In equation,

n=c/v

Spherical lens

is a piece of glass or transparent material that at least one spherical surface.

may be convex or concave.

convex lenses

Lenses that are thicker at the middle than at the edges are called

concave lenses.

those that are thicker at the edges than at the middle are called

Convex lenses

is subdivided into double convex, plano-convex, and concavo-convex.

Concave lenses

may be double concave, plane concave, or convexo-concave.

Convex lenses

are converging lenses, and these are used to correct farsightedness.

converging lenses

are diverging lenses, and these are used to correct nearsightedness

Spherical lenses

differ in their ability to refract light. Thus there is a difference in the type of image they form.

Converging lenses

produce both real and virtual images

diverging lenses

can only produce virtual images.

eye

____- is an opaque ball around 2.3 cm in diameter.

cornea

The light from the object enters the eye though the ______, the thin transparent membrane covering the eyeball.

pupil

After passing through the cornea, a portion of the light passes through the _____, an opening that regulates the amount of light entering the eye.

iris

This is made possible by the contraction or relaxation of the colored circle of the eye called the ____.

eyeball

The cast image of the object will be seen on the retina, it is at the back of the _____.

real,inverted,smaller

The image formed is  ______ inverted and ______ than the object.

Myopia

is the medical term for nearsightedness. It can be corrected by using concave (diverging lenses).

Hyperopia

can see distant objects but cannot focus clearly on nearby objects. Convex (converging lenses) can correct this vision problems.

Presbyopia

Many people aged 40 and above suffer from presbyopia. Presbyopia is called “aging eyes” or “old eyes” since it is normal consequences of growing older and it cannot be prevented.

Camera

makes up for the eye’s inability to produce a permanent record of the images formed on the retina.

is considered a mechanical eye

When focusing on an object, in a camera, the lens moves toward or away from the object.

It is a darkened box with a single small opening on one wall and a white projection screen on the opposite wall

Magnifying glass

is simply a converging lens that produces a virtual, upright, and enlarged image of an object placed at a distance less than its focal length.

microscope

is an instrument that is used in viewing small objects and microorganisms that are impossible for our unaided eyes to see.

Light microscope

is a type of microscope uses at least two convex lenses, one on the eyepiece near the observer’s eye and the other one is the objective lens located near the object being observed.

Compound microscope

is a type of microscope consists of an objective lens and an eyepiece lens.

telescope

is a device that enables people to see distant objects. It has two types-reflecting and refracting

Refracting telescope

has lenses as its objective and eyepiece.

Reflecting telescope

makes use of a concave mirror as the objective.

Generator

A generator converts Mechanical Energy to Electrical Energy.

It produces an electric current when a coil of wire is wrapped around an iron core and rotated near a magnet.

An electric generator is a device that converts mechanical energy obtained from an external source into electrical energy as the output.

How does a generator work?

Water

Hydropower plants capture the energy of falling water to generate electricity.

Water

A turbine converts the kinetic energy of the falling water into mechanical energy.

Water

Then a generator converts the mechanical energy from the turbine into electrical energy.

Wind

The wind turns the blades of the windmill, known as the turbine, which, in turn, spins the shaft that turns the coil inside the magnet, known as the generator, and it produces the electricity.

Fossil Fuel/Steam/Heat

Oil is burned to heat water which makes steam.

Fossil Fuel/Steam/Heat

Steam moves the turbine blades that turn a shaft inside the generator.

Fossil Fuel/Steam/Heat

The shaft spins the coil of wire inside a magnet in the generator that produces a current of electricity

A DC generator is an electrical machine which converts mechanical energy into direct current electricity.

What are the main components of a DC generator?

Stator

The main function of the stator is to provide magnetic fields where the coil spins.

Stator

A stator includes two magnets with opposite polarity facing each other.

Stator

These magnets are located to fit in the region of the rotor.

Rotor

A rotor in a DC machine includes slotted iron laminations with slots that are stacked to shape a cylindrical armature core.

Rotor

The function of the lamination is to decrease the loss caused due to “Eddy Current”

Commutator

A commutator works like a rectifier that changes AC voltage to DC voltage within the armature winding.

Commutator

It is designed with a copper segment, and each copper segment is protected from each other with the help of mica sheets.

Commutator

It is located on the shaft of the machine

Brushes

The Brushes are in constant contact with the commutator and are attached to the wires leading from the generator.

Brushes

The commutator spins while the brushes remain stationary, transferring current from the commutator.

Shaft

The shaft transfers mechanical energy to the generator and turns the coil through the magnetic field.

Shaft

The shaft may be turned by a turbine that operates with water, steam or air, or by other means.

AC generator produces AC electrical power whereas DC generator produces DC electrical power.

Difference between the AC Generator and the DC Generator

Back -Up power for your house

Stand-by power for businesses

Temporary power in a construction site

Permanent power to a farm

What are the top Uses of Generator?

Helping main source of electricity to supply the total power required

Pop concerts, events, and exhibitions

Caravans/Camping in remote locations Outdoor catering facilities

What are the top Uses of Generator?

Anything that changes electricity into motion, meaning electrical energy into mechanical energy is called an electric motor.

What is an electric motor?

THE STATOR

The stationary part is the stator.

Though configurations vary, the stator is most often a permanent magnet or row of magnets lining the edge of the motor casing, which is usually a round plastic drum.

THE ROTOR

Inserted into the stator is the rotor, usually consisting of copper wire wound into a coil around an axle.

When electric current flows through the coil, the resulting magnetic field pushes against the field created by the stator, and makes the axle spin

BASICS

An electric motor has another important component, the commutator, which sits at one end of the coil.

BASICS

It is a metal ring divided into two halves. It reverses the electrical current in the coil each time the coil rotates half a turn.

The commutator periodically reverses the current between the rotor and the external circuit, or the battery.

This ensures that the ends of coils do not move in opposite directions, and ensures that the axle spins in one direction.

MAGNETIC POLES

BRUSHES AND TERMINALS. At one end of the motor are the brushes and the terminals.

They are at the opposite end from where the rotor exits the motor casing.

The brushes send electrical current to the commutator and are typically made of graphite.

The terminals are the locations where the battery attaches to the motor and sends the currents to spin the rotor.