Free PHYSICS Lesson Note SS 3

This PHYSICS Lesson Note was pulled from our book ( Lesson Note on PHYSICS for SS3 MS-WORD ); Compiled to serve as reference material to help teachers draw out their lesson plan easier, saving you valuable time to focus on the core job of teaching.

The Lesson notes are based on the current NERDC curriculum (UBE compliant)

PHYSICS Lesson Note Covers The Following Topics

ELECTROMAGNETIC WAVES
ELECTROMAGNETIC INDUCTION
ELECTRIC FIELD
CURRENT ELECTRICITY
ELECTROLYSIS
ELECTRIC MEASUREMENT
MAGNETIC FIELD
MAGNETIC FIELD AROUND CURRENT-CARRYING CONDUCTOR
ELECTROMAGNETIC FIELD
ELECTROMAGNETIC INDUCTION
GRAVITATIONAL FIELD AND LAW

WEEK 1

Topic: ELECTROMAGNETIC WAVES,

TYPES OF RADIATION IN ELECTROMAGNETIC SPECTRUM,
DESCRIPTION AND USES

We can distinguish between two general classes of waves: mechanical waves and electromagnetic waves.

Mechanical waves are waves that require material medium for their propagation.

Examples of mechanical waves are water waves, sound waves, and waves on a rope. Water waves are due to vibrations of particles of water. Sound waves are due to vibrations of air particles. Water and air are the material media of propagation.

Electromagnetic waves

Electromagnetic waves are those that do not have a material medium for their propagation. They arise from the vibrations electric (E) and magnetic (M) fields. The combination of the electric and magnetic field waves is called an Electromagnetic (E-M) wave.

The magnetic and electric fields of an electromagnetic wave are perpendicular to each other and to the direction of the wave, examples of E-M waves are light wave, X-rays and gamma rays.

Another difference between mechanical and electromagnetic waves is in their velocities. Electromagnetic waves travel at the speed of light but mechanical waves travel at a speed less than that of light.

A mechanical wave may be transverse or longitudinal, but an electromagnetic wave is always transverse.

Wavelength and Frequency

Just like an ocean wave, an electromagnetic wave has peaks and troughs. The wavelength is the distance between two identical points of the wave from cycle to cycle, for instance, the distance between one peak, or crest, and the next. EMR can also be defined in terms of its frequency, which is the number of crests that pass by in a given time interval. All forms of EMR travel at the same speed: the speed of light. Therefore, the frequency depends entirely on the wavelength: the shorter the wavelength, the higher the frequency.

Types of Radiation

Electromagnetic waves were first predicted theoretically by the British Physicist, James Clerk Maxwell. He also proposed that light itself was electromagnetic radiation. The experimental evidence for the existence of E-M wave was provided by the German Physicist, Heinrich Hertz.

The term electromagnetic wave describes the way electromagnetic radiation (EMR) moves through space. Different forms of EMR are distinguished by their wavelengths, which vary from many yards (meters) to a distance smaller than the diameter of an atomic nucleus. The full range, in increasing order of wavelength, goes from gamma rays, X-rays, ultraviolet rays, visible light, infrared rays, microwaves and radio waves and is known as the electromagnetic spectrum. Electromagnetic waves have many applications, both in science and in everyday life. The different rays that constitute the spectrum all have the same basic property that they travel with the speed of light. In vacuum this speed is 3 x 10⁸ ms^-1and is represented by the letter c. They also all exhibit the properties of reflection, refraction and interference diffraction.

They however differ in their wavelength (and frequency). Recall that wavelength (λ) and frequency (f) are connected by the relation

λ = v/f or v = fv

Here v = c, the velocity of light. Hence we can write

λ = c/v or c = f

The waves also differ in the way they interact with the matter. This way, which depends on their frequency, influences how we can detect each type of wave. Hence the waves in the various parts of the electromagnetic spectrum differ in the means of production and detection.

Uses of Electromagnetic Waves

Cosmic Rays – Hazard

Gamma Rays – Killing Cancer Cells

X-Rays – Medical Uses (X-Raying People)

Ultra Violet – Sterilizing and sun tanning

Visible Light – Violet light has a higher frequency and lower wavelength than red light. (Light we see, photography is a use).

Infra-Red Light – Night Vision, short distance communication and heating

Microwaves – Cooking, communication

Radio Waves – Include short wave radio, medium wave and long wave radio waves.

Radio: Yes, this is the same kind of energy that radio stations emit into the air for your boom box to capture and turn into your favorite Mozart, Madonna, or Justin Timberlake tunes. But radio waves are also emitted by other things … such as stars and gases in space. You may not be able to dance to what these objects emit, but you can use it to learn what they are made of.

Microwaves: They will cook your popcorn in just a few minutes! Microwaves in space are used by astronomers to learn about the structure of nearby galaxies, and our own Milky Way!

Infrared: Our skin emits infrared light, which is why we can be seen in the dark by someone using night vision goggles. In space, IR light maps the dust between stars.

Visible: Yes, this is the part that our eyes see. Visible radiation is emitted by everything from fireflies to light bulbs to stars … also by fast-moving particles hitting other particles.

Ultraviolet: We know that the Sun is a source of ultraviolet (or UV) radiation, because it is the UV rays that cause our skin to burn! Stars and other “hot” objects in space emit UV radiation.

X-rays: Your doctor uses them to look at your bones and your dentist to look at your teeth. Hot gases in the Universe also emit X-rays.

Gamma-rays: Radioactive materials (some natural and others made by man in things like nuclear power plants) can emit gamma-rays. Big particle accelerators that scientists use to help them understand what matter is made of can sometimes generate gamma-rays. But the biggest gamma-ray generator of all is the Universe! It makes gamma radiation in all kinds of ways.

The following puts waves in order of increasing wavelength and decreasing frequency.

Questions

The electromagnetic waves with the highest frequencies are called
Gamma rays B. X-rays C. Ultraviolet rays D. Infrared rays
In a vacuum all electromagnetic waves have the same what?
wavelengths B. Frequency C. Propagation Speed D. Characteristics
A certain radio station is assigned a frequency of 2000KHz. Estimate the wavelength of its radio wave.
210m B. 150 m C. 201 m D. 170 m
Which of the following is not an electromagnetic radiation?
X-ray B. Radio waves C. Infrared radiations D. Sound waves.
In which of the following groups are the radiations arranged in the increasing order of their wavelength?
Radio waves, gamma rays, X-rays
X-rays, gamma rays, radio waves
Gamma rays, radio waves, X-rays
Gamma rays, X-rays, radio waves