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Light is a type of transverse wave that consists of magnetic and electric fields. Itundergoes several phenomena such as reflection and refraction.

UNDERSTANDING REFLECTION OF LIGHT

The figure og 1.1 shows the reflection of light irected on the surface of a planemirror. The line drawn at aright angle yp the mirrors surface is known as the normal line.

The law of reflaction state that:

The incident ray, the reflacted ray and the normal line all lie on the same

plane.

The incident angle, i = reflected angle, r.

While in figure 1.2, the image produced on a plane mirror is:

Virtual

The same size as the object

Upright

Laterally inverted

The object distance,

u = the image distance, v

The girl uses her right hand to com her hair but the image appears to be using her lefthand in the plane mirror. This characteristic is known as laterally inversion where the left

and right sides are interchanged

Figure 1.1 Figure 1.2

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EFFECTS OF REFRACTION OF LIGHT

1. BENDING OF A PENCIL

Figure 1.3 shows a mirror periscope which is used to view objects at an elevated

position behind an obstacle. The two plane mirror are placed 45 anticlockwisefrom the vertical axis where the second mirror is placed parallel to the first mirror.

The light rays from the objects are reflected by the first mirror at an incident

angle, i of 45 and the reflected angle, r is also 45 as

i = r. The reflected rays are subsequently reflected by the second mirror. Theimage produced is upright and laterally inverted.

2. REAR-VIEW MIRROR OF CAR

Rear-view mirror on the side of a car are used by the driver to view the vehiclesbehind or alongside his car.

3. FIRE ENGINE

The word ABMOB which is the lateral inversion of BOMBA is readable as

BOMBA when reflected by the interior rear-view mirrors of other cars in front ofthe fire engine.

4. ANTI-PARALLEX MIRROR IN AMMETER

The plane mirror behind the pointer in the ammeter show in figure 1.4 produces

an image of the pointer when the eye of the observer is not in line with the pointerwhile taking the reading. When the eye is vertically above the pointer, the image

of the pointer will not be seen on the mirror and the correct reading can be

obtained.

Figure 1.3 Figure 1.4

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REFLECTION OF LIGHT ON CURVED MIRRORS

COMMON TERMINOLOGY

Principal axis:

A line which passes through the center of curvature, C and the pole of the curved

mirror, P.

Pole of mirror, P:

The center point of a curved mirror.

Center of curvature, C:

The geometric centre

the pole of mirror, P

Aperture of mirror:

The portion of the surface of the mirror that reflects light

of a curved mirror.

Focal point,F :

A point where rays parallel to the principal axis converge at or diverge from.

Focal point, f:

The distance between the focal point, F and the pole of mirror, P

Radius of curvature, r = 2f;

The distance between the center of curvature, C and

Aperture of mirror:

The portion of the surface of the mirror that reflects light

Object distance, u:

The distance between the object and the pole of mirror, P

Image distance, v:

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The distance between the image and the pole of mirror, p

DIFFERENCES

Concave mirror Convex mirror

Curve towards object Curves away from object

Rays parallel to the principal axis converge

at the real focal point, F which is situated

in front of the mirror

Rays parallel to the principal axis diverge

from the virtual focal point, F which is

situated behind the mirror

Positive focal length.

Example: +15 cm

Negative focal length.

Example: - 15 cm

RAY DIAGRAMS

A ray diagram is used to determine the characteristic and positions of image for various

object distances. A real images is formed when two or more real rays originating from apoint of the object intersect. A real image is formed in front of a mirror. A virtual imagesis formed when two or more virtual extended rays intersect. A virtual image is formed

behind a mirror.

Concave mirror

Convex mirror

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UNDERSTANDING REFRACTION OF LIGHT

The straw in the glass of water is seen as a broken straw due to the refraction of light.

Refraction of light is a phenomenon where the direction and velocity of light are changed

when it passes thought the boundary of two transparent materials of different opticaldensities.

optical densities = physical densities

(p = m/V), for example, paraffin is optically denser than water but physically less densethan water.

EXAMPLE OF REFRACTION

A) When light travels from air (optically less dense) to water (optically denser):

i. i > r

ii. velocity of light decrease in water and cause the light ray to bend toward the

normal

B) When light travel from water (optically denser) to air (optically less denser)i. i > r

ii. velocity of light decrease in water and cause the light ray to bend away the

normal

C) When light travels at a right angle to the boundary between two mediums:

i. i= r= 0

ii. no refraction occurs and the ray is not bent but the velocity still changeaccordingly

LAW OF REFRACTION

The incident ray and the refracted ray are on the opposite sides of the normal at the point

of incidence and all three lie in the same plane. The value ofsin i/ sin r = Constance (snells law)

REFRACTIVE INDEX, n

The refractive index, n = sin i/sin r where n is dimensionless (no unit). It is an indication

of light-bending ability of a medium. The refractive index of a medium that contains therefracted ray and refracted angle, r. ( for example, n shows that the refracted angle, r is

positioned in water). A medium with hight value of n bends light more, hence has greater

refracting effect while a medium with low value of n bends light less and has lees

refracting effect.

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REFRACTIVE INDEX , n AND SPEED OF LIGHT

The speed of light in air/vacuum is 3 x 10 m s and when light travels from air to an

optically denser medium, the speed of light decrease where:n= c/v= speed of light in vacuum/speed of light in the medium

The value of n>1 for all mediums because the speed of light in a vacuum is always higherthan the speed of light in other materials.

REL DEPTH, D AND APPARENT DEPTH, d n

A swimming pool normally appears shallower than it really is due to the refraction of

light. The refractive index of water, n = D/d.

EFFECT OF REFFRACTION OF LIGHT

The twinkling of the star:

The star twinkle because we view them through thick layer of moving air (turbulent) in

the earths atmosphere. The star do not twinkle when observed in outer space. The

densities or refractive indices of the layer of the atmosphere are varied by the moving airand when light rays from the star travel refracted rapidly. As the result, the light enters

the eye at one moment and does not at the next moment. This constant but random

change produces the twinkling of star. The moon and planet do not twinkle as theirapparent sizes are not affected by the small fluctuation of the atmospheric refraction.

Therefore there is not effect to the amount of light that enter the eye.

UNDERSTANDING TOTAL INTERNAL REFKECTION

Total internal reflection is a reflection of light rays at the boundary of two medium whenthe incident angle, I is larger than the critical angle, c of the optically denser medium.

The critical angle, c of a medium is the maximum incident angle before total internal

reflection occurs (when the refracted angle, r = 90). The boundary of the two mediums

acts as a perfect plane mirror. Two conditions for total internal reflection to happen:a) The incident angle, i>critical angle, c.

b) The light travels from an optically denser medium to an optically less

dense medium

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RELATIONSHIP BETWEEN CRITICAL ANGLE, c AND THE REFRACTIVE

INDEX, n

A light ray traveling from water to air with its incident angle, I equal o the critical angle,

c of water and the refracted angle, r = 90. In order to determine the refractive index, n ofwater using Snells law

(n = sin i/ sin r), the refracted angle must be situated in water. Therefore the direction of

the light ray has to be reversed. Using Snells law:Refractive index of water,

n = sin i /sin r =sin 90/ sin c.

NATURAL PHENOMENA AND THE USES OF TOTAL INTERNAL REFLECTION

Fishs Eye View

A fish is able to see an object above the water surface due to the refraction of light and itis also able to view an object behind an obstacle due to the total internal reflection.

Prism Binoculars

The prism binoculars are also based on the effects of glass prism on light rays. On one

section of a binoculars, the twoglass prisms are arranged with their hypotenuse faced parallel but diagonally

perpendicular to each other. The image produced is virtual, upright and not laterally

inverted. The distance between the objective lens and the eyepiece of the binoculars isshort compared to an astronomical telescope, thus making it portable.

UNDERSTANDING LENSES

Power of Lenses, P

The lenses power, P is the ability to converge or diverge an accident light ray. It is the

reciprocal of the focal length, f of a lens, in metres.P = 1/f(m) or P = 100/f(m)

The unit of lens power is m or

diopter, D.

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Ray Diagrams

A ray diagrams is used to determine the characteristic and positions of image for various

object distance.

Convex Lens:

Concave Lens:

Image Formed by a Concave Lens

The characteristic of image formed; virtual, upright, diminished and formed on the same

side as the object for all object distances. The image distance, v is always less than the

object distance, u. the concave lens can be used in spectacle for myopia (shortsightedness).

Lens Equation

The relationship between the object distance, u, the image distance v and the focal length,

f of a thin lens is given by the lens equation:1/f = 1/u + 1/v,

The equation is used with the following:

The lens equation can be used to determine

the position of an image an the linearmagnification.

Convex

lens

Concave

lens

Object

distance, u

Positive positive

Image

distance, v

Real

image-

positive

Virtualimage-

negative

Virtual

image-

negative

Focal

length, f

positive Negative

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THE USES OF LENS IN OPTICAL DEVICES

Magnifying glass (simple microscope)

When an object is placed at a distance, u of less than the focal length, f of a convex lens,

the lens acts as a magnifying glass. The two rays from the top of the object do not

converge after passing through the lens. Instead, they intersect at point p when they areextended backward. The image produced is virtual, upright and magnified.

Slide Projector

Component function

Lamp/ bulb Light source which is placed at the centre

of curvature of the concave mirror so that

the light rays fall normally on the concavemirror

Concave mirror To reflect the light rays through the optical

centre of the condenser lens

Condenser lens Consists of two plano-convex lenses which

converge the light rays from the mirrortowards the slide to brighten the slide

completely

Heat filter To prevent the projector from overheating

by absorbing heat

Slide Placed between f and 2f of the projection

lensProjection lens To focus the image onto the screen

screen A real, inverted and magnifying image is

formed on it

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UNDERSTANDING THE

NUCLEUS OF AN ATOM

The Composition of the Nucleus

of an Atom

An atom consist of a nucleus with

electrons orbiting the nucleus.

The nucleus which is made up ofproton

And neutrons is very dense. Neutrons and protons are called nucleons. Most of the mass

of the atom is in the nucleus itself. The electrons move around the orbit.

The Structure of Atom

An atom is mostly empty space with move subatomic particles concentrated in thenucleus. The table below shows the properties of the subatomic particles.

Proton Number (z) and Nucleon Number (A)

Proton number is the number of protons in the nucleus of an atom. Nucleon number is the

total number of protons and neutrons in the nucleus of an atom. A neutral atom has equal

numbers of protons ans electrons. Therefore the protons number also show the number ofelectrons in a neutral atom. The number of neutrons, is found by subtracting the protons

number from the nucleon number.

Number of Neutrons, N = A-Z

Subatomic

particles

Symbols Actual

mass

Relative

mass

Value

of

charge

Relative

charge

Electron e 9.1x

10 kg

1/1840 -

1.60x10 c

-1

Proton P 1.67 x

10 kg

1 +1.60x

10 c

+1

Neutron n 1.67 x

10 kg

1 0 Neutral

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Nuclide and Nuclide Notation

A nuclide refers to a particular type of atom characteristic by its proton number andnucleon number. The nuclide notation of an the element, the nucleon number and the

proton number. An element, X with nucleon number, A and protons number Z is

represented by the symbol below.

Element Nuclide

notation

Proton Electro

n

Neutrons

Hydrogen 1 1 0

Nitrogen

7

7 7

Silver 47 47 61

The table shows a few example of nuclide notation. The nuclide notation for a proton, an

electron and neutron are

P , e, n respectively.

Isotopes

A sample of an element usuallyConsistof a mixture of different type of atom. The different type of atom have the same

protons number but different nucleon number. Atom of an element with the same proton

number but different nucleon number are known as isotopes. The chemical propertise ofan atom is determine by the number of electron in the atom. Therefore isotopes of an

element have similar chemical propertiese.

ANALYSING RADIOACTIVE DECAY

Radioactivity:

Radioactivity is the spontaneous disintegration of an unstable nucleus accompanied bythe emission of energetic particles or photons. The emission of energetic particles or

photons is called radioactive emission. All nuclei with z>83 or A >209 are unstable.

Unstable isotopes undergo radioactive disintegration or decay. Stable isotopes do notundergo radioactive disintegration.

Cloud Chamber:

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The particle or radiation travelling in a cloud chamber ionises the air situated with

alcohol inside. The ions formed allow vapour to condense, forming tiny alcohol droplets.As a result, visible track can be seen.

Photographic Plate or Film:

When the photographic plate is exposed to radiation, a chemical reaction occurs which

causes the photographic plate to be darkened. The degree darkened depends on theamount of radiation the plate is exposed to. Workers in nuclear power satation or

laboratories wear film badges which contain a photographic film to monitor their

exposure to radiation.

Radioactive Decay:

A radioactive decay is a process where an unstable nucleus emits radiations in order to

become a more stable nucleus.It also a spontaneous and random process as:

a. The rate of decay cannot be controlledb. It happen on its own

c. It is not effect by chemical composition or physical factors such as

temperature,pressure, electric fields and magnetic fields.

It is a random process since it is impossible to predict which atom will decay at anymoment of time. The unstable nucleus is called the parent nuclide. After radioactive

decay, the resulting nucleus which is more stable is called the daughter nuclide. There are

three types of radioactive decay:

a. Alpha decay

b. Beta decayc. Gamma decay

Alpha Decay:

An alpha particles is a helium nucleus which consists of two neutrons and two protons. It

has a charge of + 2e. During alpha decay, the radioactive parent nucleus loses two

protons and two neutrons in tha form of alpha particles. As a result, the proton number of

the parent nucleus decreased by 2 while the nucleus number decreased by 4

Beta Decay:

A beta particles is an electron with a charge of-1e. during beta decay, a neutron

disintegrates into a proton and a neutron. The equation for the disintegration pf neutron is

nP+e. The protons remains in the nucleus but the electron is ejected from the nucleus at

hight speed. As the result, the proton number of the parent nucleus increase by 1 while

the nucleon number is charged.

Gamma Decay:

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Gamma emision is an energatic electronmagnetic radiation. Certain unstable nucleus in

an excited state emits gamma rays in order to become more stable nucleus. The nucleusafter the emission become less energatic. As gamma ray is not a particles, the protons

number and nucleus number remain unchanged.

Radioactive Decay Series:

It shows a series of successive decay for a particular radioisotopes until a stable isotopesis achieved. It is displays on a graph of nucleon number, A or neutron number, N against

proton number, Z. Figure below shows the example of decay series:

:

The Concept of Half-Life:

The decay of a radioactive nucleus is a random and spontaneous process. As a result, it is

not possible to predict when a particular nucleus will decay. Nevertheless, the number of

nuclei which disintegrates over a certain period of time can be determined if there is alarge number of nuclei. As time passes, the number of nuclei disintegrated increase and

the number of nuclei remaining decrease. The half-life of a radioactive element is the

time taken for half the radioactive nuclei in a given sample to decay.

Radioisotopes Half-life

Uranium-238 5000 million

Plutonium-239 24000 years

Radium-228 1600 yearsCalcium-137 30 years

Cobalt-60 5 years

Radon-222 4 days

Sodium-24 16 hours

Nitrogen-13 10 minutes

Barium-143 12 second

UNDESTANDING THE USES OF RADIOISOTOPES

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Atomic Mass Unit (A.M.U. or U):

The atomic mass unit is a unit used to measure the masses of particles. The mass of one

carbon-12 atom is defined as a mass of 12u. the mass one carbon-12 atom is 1.99265 x

10:Hence, 12u = 1.99265 x 10 kg

u= 1.99265 x 10 kg /12

= 1.66 x 10 kg

Nuclear Fission:

It occurs when a heavy nucleus splits into two or more nuclei of roughly equal masseswith the releases of several neutrons. Nuclear fissions is initiated when a heavy nucleus is

bombarded by a neutron. The fissions fragment fly apart at great speed. Hence, the

fragments have larger amounts of kinetic energy. The kinetic energy is converted to heat

energy when the fragments collide with the surrounding atoms.

Chain Reactions:

It occurs when neutrons from the fissions of uranium-235 continue to split other nuclei

causing further collision. The number of nuclei increases rapidly. As a result, the chain

reaction takes place at a higher rate. The chain reaction continues if a minimum of oneneutrons from each fissions triggers further fissions. The mass of uranium sample must

also exceed a certain minimal mass known as the critical mass. The critical mass is

determined by its shape. A controlled chain reaction takes place in a nuclear powerstation. Uncontrolled chain reactions take place in nuclear weapons.

Nuclear Fissions:

It occurs when two or more small and light nuclei combine to form a heavier element. A

large amount of energy is released during nuclear fusions. The reactions which power thestar is nuclear fusion.

Energy in a Nuclear Reaction:

In a nuclear reaction, the total mass of the daughter particles and other products is less

than that of the parent particles. The difference in mass is called mass defect or mass

loss. According to Einsteins Principle of Mass-Energy Conservation, the mass defect isconverted to energy given by:

E=mc

Where E=energy released, in Jm=mass defect, in kg

c= speed of light, in m s

Generation of Electricity from Nuclear Reaction

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Electricity can be generated from nuclear reaction in a nuclear power station which

consist of a nuclear reactor and a generator. The energy released from the nuclearreaction heats the water. The steam prodused is used to drive turbines which in turn drive

the electrical generators.

Component FunctionModerator Slows down fast moving neutrons so that

nuclear fissions can occurs. Water can also

be used as moderator.

Core Nuclear fissions occurs in the uranium rod

Control Controls rate of fissions by absorbing

some neutrons

Concrete wall Prevent the radiation from escaping

Turbin Turns the dynamo in the generator to

produce electrical energy

Advantage Disadvantage

Producing of energy involves a lower cost High cost of building a nuclear power

stations

Nuclear reactors are relative safe Accidents due to human error may occur

Does not emit greenhouse gases such as

carbon dioxide

Waste from nuclear stations have long-half-

live and need be stored to using expensive

methods

The dwindling reserves of fossil fuels

requires the uses of alternative source of

energy

Nuclear fuel is not easy to obtain

Nuclear reactors are used to solve problems involving:

a. The production of artificial radioactive isotopes for medical diagnosis and

treatmentb. The testing of theory on subatomic particles

c. The productions of fissionable transuranic element such as plutonium from

uranium-238

REALISING THE IMPORTANCE OF PROPER MANAGEMENT OF RADIOACTIVE

SUBSTANCE

The Negative Effects of Radioactive Substance:

Radioactive substance produce ionising radiations such as alpha particles, beta particlesand gamma rays. These ionising radiation remove electrons from the surrounding atoms

and produce ions pairs. The ionisation of atoms may cause alteration in genetic material

of the cell such as the deoxyribonuclei acid (DNA). Products formed due to ionisationmay also have toxic effects on the metabolic process. The effect on the cell include:

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a. Abnormal replication

b. The cease of function in the cell

c. Death of cellTable below shows two categories of the harmful effects of radiation on human.

Somatic effect Genetic effect

Fatigue Abnormal reproductive cellOrgan failure Birth detects

Hair loss Premature death

Vomiting Genetic defects such asa. Down syndrome

b. Klinefelter syndromec. Turner syndrome

Skin burn

Leukemia

Safety Precautions in the Handling of Radioactive Substance:

Workers handling radioactive substances wear special badges or dosimeter to detects the

level of exposure to radiation. Experiments using radioactive substances are to be

conducted in a room enclosed by thick concreate walls. Food and drinks are prohibited in

radiation laboratories. And others common rule.