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# Lesson Note on Physics SS3 Second Term

## SCHEME OF WORK

WEEK 1 AC IN RESISTOR, INDUCTOR AND CAPACITOR

WEEK 2 ALTERNATING CURRENT CIRCUIT

WEEK 3 MODEL OF ATOMS

WEEK 4 TRANSFORMATION OF ELEMENTS

WEEK 6 QUANTUM

WEEK 7 PHOTOELECTRIC EFFECT

WEEK 8 CONDUCTION OF ELECTRICITY IN GASES

WEEK 9 WAVE NATURE OF MATTER

# Below are the 2022 complete Physics lesson notes for SS3 Second Term

Week 1

TopicALTERNATING CURRENT CIRCUIT

ALTERNATING CURRENT

A.C. circuits are circuits through which an alternating current flows. Such circuits are used extensively in power transmission, radio, telecommunication and medicine.
Alternating currents are produced by time-dependent alternating voltages given by the relation E = E0 sin ωt. Much of what we learned about d.c. circuits also apply to a.c. circuits. The effects on such voltages on resistors, capacitors and inductors will be discussed.
Nomenclature in A.C Circuits
An Alternating Current (A.C.) is one that varies sinusoidally or periodically, in such a way as to reverse its direction periodically. The commonest form of such an a.c. can be represented by
I = I0 sin 2πft
I0 sin ωt

Week 2

Topic: AC IN RESISTOR, INDUCTOR AND CAPACITOR

Alternating current

Direct current (DC) circuits involve current flowing in one direction. In alternating current (AC) circuits, instead of a constant voltage supplied by a battery, the voltage oscillates in a sine wave pattern, varying with time as V = Vo sin ωt.

In a household circuit, the frequency is 60 Hz. The angular frequency is related to the frequency, f, by ω = 2πfVo representing the maximum voltage, which in a household circuit in North America is about 170 volts. We talk of a household voltage of 120 volts, though; this number is a kind of average value of the voltage. The particular averaging method used is something called root mean square (square the voltage to make everything positive, find the average, take the square root), or rms. Voltages and currents for AC circuits are generally expressed as r.m.s. values. For a sine wave, the relationship between the peak and the r.m.s. average is:

r.m.s. value = 0.707 peak value

Week 3

Topic: MODEL OF ATOMS

Thompson Rutherford Model

Modern atomic theory provides a reasonably satisfactory explanation of the properties of matter, the mechanisms of chemical change and the interaction of matter and energy. Such a theory emerged from the synthesis of the work of several scientists, only a few of which will be discussed here.

John Dalton (1766-1844) is generally credited as the father of the atomic theory but the early Greek philosophers were the originators of the concept of atoms. They taught that matter is composed of atom and is therefore finitely divisible, John Dalton considered the atom as constituting the simplest component of matter. He viewed the atom as ‘indestructible’, tiny hard spheres. The discovery of radioactivity by Henry Becquerel (1891 showed that atoms are complex rather than ‘indivisible’ or ‘indestructible’ but can disintegrate forming atom of different elements. The discovery of cathode rays in electric discharge tubes (1895) by William Crookes revealed that negatively charged electrons were components of the atom.

Week 4

Radioactivity refers to the particles which are emitted from nuclei as a result of nuclear instability. Because the nucleus experiences the intense conflict between the two stronger forces in nature, it should not be surprising that there are many nuclear isotopes which are unstable and emit some kind of radiation. The most common types of radiation are called alpha, beta and gamma radiation, but there are several other varieties of radioactive decay.

Composed of two protons and two neutrons, the alpha particle is a nucleus of the element helium. Because of its very large mass (more than 7000 times the mass of the beta particle) and its charge, it has a very short range. It is not sustainable for radiation therapy since its range is less than a tenth of a millimeter inside the body. Its main radiation hazard comes when it is ingested into the body; it has great destructive power within its short range. In contact with fast-growing membranes and living cells, it is positioned for maximum damage.

Week 5

Topic: Transformation of Elements

Transformation of Elements

The phenomenon of radioactivity was first discovered by Henri Becquerel

Natural radioactivity is the spontaneous disintegration of the nucleus of an atom during which α-particle or β-particle, or gamma rays or a combination of any or all the three and heat (or energy) are released.

When a radioactivity element undergoes radioactive decay, it may emit either α-particle, β-particle or γ rays. This changes the atomic number of the element, hence a new element is formed. For example, Radium-226 decays by emitting an α-particles to turn into a new element Radon. Radium-226 has a mass number 226 and an atomic number 88 and hence it is denoted by 22688Ra. The α-particles it emits is a Helium nucleus denoted by 42He. So when Radium 226 emits an α-particle. We can write a nuclear equation:

22688Ra → 42He + 22286Rn + energy

Week 6

Topic: QUANTUM

INTRODUCTION

Some of the important postulates of Bohr’s model of the atom were that the electrons moved around the nucleus in specified orbits. In these orbits they can move without radiating energy.

They can acquire or lose energy only in discrete units called quanta. Thus Bohr suggests that electrons in the atom exist in discrete (or quantized) energy states.

In 1902, Max Planck was able to show that experimental observations in the radiation emitted by substances could be explained on the basis that the energy from such bodies emitted in separate or discrete packets of energy known as energy quanta of value hf, where f is the frequency of radiation and h is a constant known as Planck’s Constant. Thus the energy E of the quantum of radiation or photon is given by E = hf.

This is known as Planck’s theory of radiation. The term quantum means amount fixed amount, or discrete or separate amount as distinguished from a continuous quantity.

Week 7

Topic: PHOTOELECTRIC EFFECT

INTRODUCTION

In 1887, photoelectric effect was invented by the scientist H. Hertz. When we passing a light into a material, the material should emit an electrons. This effect is called as Photoelectric effect. Some of the rays produced in Photoelectric Effect are x-rays, ultraviolet rays and γ-rays.

Einstein’s says that every photon or a quantum of light has an energy value hν. Electrons are located inside the surface of the metal. There may be some amount of work W should be required for an electron to come out of the metal. If the transferred energy is high comparing the internal attractions then the electrons gets liberated. In this the one photon can release a one electron. This is nothing but the Photoelectric Effect. Let us study more about the Photoelectric effect in this section.

Week 8

TopicCONDUCTION OF ELECTRICITY IN GASES

INTRODUCTION

Electrons: When a high tension discharge passes between electrodes sealed into a partially evacuated vessel, the gas becomes luminous showing a series of highly colored glows which are often very beautiful.  If the pressure is sufficiently reduced, a series of streams appears, proceeding in straight lines from the cathode.  These streams are known as “cathode rays,” and are found to be independent of the position of the anode, and often penetrate regions occupied by other glows in the tube.    The researches of modern physics have shown that these rays are streams of discreet particles of negative electricity, called “electrons.”  Their properties do not depend upon the material of the electrodes nor the nature or presence of the gas through which the discharge takes place.  They may be produced from all chemical substances, and consequently must play an important part in the structure of matter.  The velocities with which they move through the tube vary from one-thirtieth to one-third that of light.  The ratio of the charge of an electron to its mass is constant and is equal to 1.77 X 107electromagnetic units per gram. The charge of an electron is 1.5 X 10-20 electromagnetic units and Themass is about 1/1800 thatof the hydrogen atom.

Week 9

Topic: WAVE NATURE OF MATTER

Electron Diffraction

The wave nature of X-rays was established by X-ray diffraction experiments. In the same way the Davisson and Germer experiment established the wave nature of electrons.

In the Davisson and Germer experiment, a beam of electrons emitted from a heated filament was made to impinge on a layer of a thin metal film or crystal at C. The electrons were diffracted and the diffraction rings were produced on a photographic plate placed behind the thin metal film as shown below.

If the voltage V on the anode was increased, the velocity, v, of the electrons was increased. The rings were then seen to become narrower. Hence the wavelength, λ, of the electron waves decreases with increasing electron velocity.

Week 10