ENERGY QUANTIZATION

Suggests that energy is emitted from heated bodies in discrete or

separate packets know ENERGY QUANTA.

Thus the energy E of the quantum of radiation or photon is given

by E = hf.

Planck’s theory of
radiation

The term quantum means amount fixed amount, or

discrete or separate amount as distinguished from a

continuous quantity.

The energy of an electron is given by the radiation
E = 1/n2 R

N = electron’s quantum number and R is a constant
En is the energy in the excited state
E0 is the energy in the ground state (n = 1)
En - E0 = hfn = hc/

The energy of each radiated photon is proportional to
the length of its corresponding arrow as shown in fig 11.4

Examples 11.1 and example 11.2

1. Which of the following correctly represents the unit of elastic constant?
(A) Kgms - 1

(B) Nm

(C) Kgs - 2 (D)Nms - 2

(2) The two positions of a body undergoing a uniform accelerated
motion are (10s, 10m/s) and (30s, 50m/s) on the velocity graph. Calculate
the magnitude of the acceleration of the body.
(3) A car starts from rest and accelerates uniformly for 20s to attain a
speed of 25m/s.
It maintains the speed for 30seconds before decelerating uniformly to
rest. The total time for the journey is 60s. (i) Sketch a velocity-time graph
for the motion.

(ii) Use the graph to determine deceleration

(iii) Total distance travelled by the car.

Franck-Hertz
Experiment

ATOMIC SPECTRA : COLOUR AND LIGHT
FREQUENCY
A line spectrum is spectrum that consists
of a number of well defined lines each
having a particular frequency or wavelength
or colour.
E2 - E1 =hf
Energy transitions

(i) Emission spectra

These are spectra observed due to light emitted when the temperature of an
atom, gas or metal is raised, e.g. incandescent solid or vapour , a spark discharge,
arc discharge, the discharge of electricity through a gas or vapour contained in a
discharged tube, etc

(ii)Line Spectra

Line spectrum is obtained from atoms in gases such as hydrogen or neon at low
pressure in a discharge tube.

(ii)Continuous Spectrum

The spectrum formed from white light contains all colors, or frequencies, and is
known as a continuous spectrum

(ii)Band SpectrumIt consists of a number of bright bands with a sharp edge

at one end but fading out at the other end. Band spectra are obtained from
molecules.

(ii)Absorption SpectrumWhen a cool gas is placed in the path of a continuous

spectrum of light, dark absorption lines will appear in the resulting spectrum

THE Photoelectric Effect:

Electrons are emitted from the surface of metals when

an electromagnetic wave e.g light, falls on the metal

surface. Energy in the form of light can cause an atom

to eject one of its electrons, but only if the frequency

of the light is above a certain value.

Photo- cell. Fig 11.5

A photocell is a resistor that changes
resistance depending on the amount of
light incident on it. A photocell operates on
semiconductor photoconductivity: the energy of
photons hitting the semiconductor frees electrons to
flow, decreasing the resistance.

USES OF PHOTOCELLS
Burglar alarm
Television cameras
Automatic doors
Automatic street light
Automatic digital counters

Einstein's equation and explanation

Spectra

E = E0 – E1

X RAY

PRODUCTION

CHARACTERISTIC

PRACTICAL APPLICATION

HAZARDS

X RAY
Are the electromagnetic radiations of very small wavelength ranging between
0.03 and 3 nanometres
X ray production

Mode of operation
TYPES OF X RAYS
HARD X RAYS with short wavelength which are strong,deeply penetrating
and are higly destructive
SOFT X RAY
Are less penetrating and have longer wavelength
PROPERTIES OF X RAY
*They pass through material more or less unchanged
*They cannot be refracted
*Electric and magnetic field does not have any effect on these rays
*These radiations ionise the surrounding air by discharging electrified bodies

*They have short wavelength varying between 0.1 to 1A
*They are produced when metal anode is bombarded by very high
energy electrons
*They are electromagnetic waves and do not require any medium
for propagation
*X rays cannot be focused on a single point
*They cause photoelectric emission
*Intensity of x rays depends on number of electrons hitting the
target
*Continuous spectrum appears due to retardation of electrons

USES OF X RAYS

1. In diagnostic medines
2. Computer tomography (CT scans)
3. Therapeutic techniques i.e cancer treatment
4. Used for crystallography, astronomy, microscopy,

industrial radiography, airport security, spectroscopy,
fluorescence and ti implode fission devices

5. Create art and to analyse painting

HAZARD OF X RAYS
1. Biological damage
2. Cells can be damaged or killed
3. Prolonged exposure to x- rays may cause cancer
4. Possess the ability to damage tissues and cause

leukaemia

SAFETY PRECAUTION
The radiologist handling X rays should wear lead coats
and gloves
The face should be covered
They should undergo routine health checkups.