Month: April 2023

Bohr’s Atomic model

Bohr’s Atomic model explain many of the atomic phenomena. He postulated three fundamental laws to overcome the inconsistency in the Rutherford model.

Postulate 1:- Electrons can not occupy states at all energy levels. Electrons can occupy states at only certain discrete energy levels. When electron occupies a discrete energy level, it does not emit radiation and is said to be Stationary (or Non-radiating state).

Postulate 2:-When an electron moves from Higher energy state (E2) to lower energy state (E1).It emitts radiation at a frequency given by 

f= (E2 – E1)/h. 

where ‘h’ is the plank’s constant h= 6.62 X 10-34 Joules. E1 and E2 are Energies in Joules.

Postulate 3:- Any stationary state is determined by the condition that the angular momentum of the electron in this state is quantized and is a multiple of h/2π .

angular momentum = Integral multiple of h/2π .

mvr = nh/2π.

The total energy of electron in stationary state is Wn = (-13.6/n2 ) eV.

Input and output characteristics of a transistor in Common Collector configuration

Common collector configuration, As we know collector is kept common to both input and output terminals.

To draw input and output characteristics of Common collector. The circuit diagram is given as follows

input characteristics:-

These are in between input current  (IB) Vs input voltage (VBC) with output voltage (VEC) as kept constant.

To obtain input characteristics , VEC is kept constant and VBC is increased in equal steps and the corresponding increase in IB is noted and the same procedure is repeated for different values of VEC and the characteristics are shown in the previous figure.

output characteristics:-

The output characteristics are obtained by keeping input current as constant (IB = constant)  and the output voltage VEC is increased in suitable steps and the corresponding output current IE is noted down.

This is repeated for different values of IB .

Receiver Characteristics

The following are the Receiver characteristics

  1.  Sensitivity.
  2. Selectivity.
  3. Fidelity.
  4. Image frequency Rejection ratio.
  5. tracking.

1.Sensitivity:- It is defined as the ability of a radio receiver to amplify weak signals. In another way that is the voltage that must be applied to the receiver input terminals to give a standard output power, measured at the output terminals.

  • Sensitivity is often expressed in micro volts (or) in decibels below 1 volt and measured at three points along the tuning range when a production receiver is lined up.
  • for example Sensitivity can be expressed as  at 100 KHz a particular receiver has a sensitivity of 12.7 μV (or) -98dBV (dBV means decibels below 1V). 12.7 μV for a signal to Noise ratio of 20 dB in the output of the receiver.
  • For professional receivers, Sensitivity can be expressed as signal power required to produce a minimum acceptable output signal with a minimum acceptable Signal-to-noise ratio.
  • The curve, which is a plot of sensitivity of a good domestic receiver.
  • Sensitivity of a portable and other small receivers used in the broadcast band is in the presence of 150 μV.
  • where as Communication receivers may have better than 1 μV in the High Frequency band.

Sensitivity of a Superheterodyne receiver is determined by the following

  1. The gain of Intermediate Frequency Amplifiers.
  2. The gain of Radio Frequency Amplifiers.
  3. The Noise Figure of the Receiver.

2. Selectivity:- 

  • The Selectivity of a receiver may be defined as the ability to reject unwanted signals.
  • Typical Selectivity curve is shown below.
  • This figure shows the attenuation that the receiver offers to signals at frequencies near to the one to which it is tuned.
  • Selectivity is measured at the end of the Sensitivity test with the same conditions.
  • The curve is plotted between attenuation in dB Vs frequency.
  • Selectivity varies with respect to received frequency (if ordinary tuned circuits are used in Intermediate Frequency section) and this selectivity becomes worse when the received frequency increases.
  • Selectivity determines the adjacent channel rejection of a receiver.

3. Fidelity:- 

  • Fidelity is the ability of a receiver to reproduce all the modulating frequencies equally.
  • The fidelity of the receiver basically depends on the Audio frequency Amplifier frequency response.
  • High fidelity is essential in order to reproduce a good quality music faithfully in audio applications that is with out introducing any distortion.
  • for this it is essential to have a flat-frequency response over a wide range of audio frequencies.
  • ideally the frequency response is flat over Audio Frequency range but practically, it decreases in the lower and higher cut off frequency sides.

 

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Double spotting

This is a well known phenomenon which manifests itself by the picking up of the same short wave station at two nearby points on the receiver dial.

  • It is causal because of poor front end selectivity that is inadequate image frequency rejection.
  • Intermediate frequency(IF) stage takes care of eliminating different adjacent signals.
  • If there is no RF Amplifier in a receiver then it suffers badly from double spotting.
  • Suppose if a receiver having an Intermediate frequency of 455 KHz. There is a strong station 14.7 MHz and a weak station 13.79 MHz. If a receiver is turned to 14.7 MHz (strong station) then receiver picks up same station. But if Receiver is tuned to a weak station 13.79 MHz then also receiver picks up near by strong station 14.7 MHz.
  • Double spotting is harmful because a weak station may be marked by the reception of nearby strong station.
  • An improvement in image frequency rejection will reduce Double spotting.
  • One advantage of Double spotting is , it is used to calculate intermediate frequency of an unknown receiver.

Extrinsic Semi conductors (N-Type Vs P-Type)

  • Intrinsic semi conductors has a little current conduction capability.  
  • This capability can be increased by many times by just adding a very small amount of impurity in  (1 atom per 1 million pure atoms) the process of crystallization.
  • This process is called as doping 
  • Si and Ge are tetravalent (4 electrons in Valance Band) atoms. So the impurity may be either tri valent (or) pentavalent.
  • Depending on the type of impurity added extrinsic semi conductors are divided into 2 types 

i. Donor type (or) N-type.

ii. Acceptor type (or) P-type.

The detailed explanation about N-type and P-type semi conductors are given in the following table.

N-type Semi conductors P-type Semi conductors
When a small amount of pentavalent impurity such as Arsenic, Antimony, Bismuth (or) Phosphorus is added to a pure semi conductor during the crystal growth. The resulting semi conductor is called N-type semi conductor. When a small amount of trivalent impurity such as Boron, Gallium, Indium (or) Aluminium is added to a pure semi conductor in the  resulting crystal . The resulting semi conductor is called P-type semi conductor.
Where N stands for negative. Where P stands for positive.
When a pentavalent (or) a donor atom is added to Si the impurity atom forms 4 co-valent bonds with 4 Si atoms and fifth valance electron is left free. Which is loosely bound to the Antimony atom. When a trivalent (or) a acceptor atom is added to  Pure Si (or) Ge semi conductor. Boron has 3 valance electrons in its valance shell  and pure Si has 4 valance electrons in its valance shell. The 3 electrons of Boron atoms forms 3 covalent bonds with 3 Si atoms and a whole is left free which is loosely bound to Boron.
One impurity atom provides one free electron yet an extremely small amount of impurity provides enough atoms to supply millions of free electrons. simillarly a small amount of impurity provides millions of wholes.
In this type of semi conductor majority carriers are electrons which are responsible for conduction of current. Majority carriers are holes and are responsible for conduction of current.
Number of holes are very less in N-type when compared to electrons. Hence holes are known as minority carriers. Simillarly number of electrons less compared to number of holes in P-type. Minority carriers are electrons.

N-type is preferred over P-type , mobility of electron is high compared to hole mobility.

Get a list of names as an input from the user and make the first letters in caps and print each word as a list

#Get a list of name as an input from the user and make the first letters in caps and print each word as a list

n = int(input("Enter total number of names n = "))

names = []

print("\n Enter names: \n")

for i in range(0, n):
   x = input()
   names.append(x)

print("\n Names with first letters in caps are:\n")

for i in range(0, n):
   print(names[i].capitalize())

 

functions as arguments (Notes)

functions as arguments: –

1). Information can be passed into functions as arguments. Arguments are specified after the function name, inside the parentheses. You can add as many arguments as you want, just separate them with a comma. The following example has a function with one argument (fname). When the function is called, we pass along a first name, which is used inside the function to print the full name.

2).Arguments are often shortened to args in Python documentations.

3). Parameters vs Arguments: – The terms parameter and argument can be used for the same thing: information that are passed into a function. From a function’s perspective: A parameter is the variable listed inside the parentheses in the function definition. An argument is the value that are sent to the function when it is called.

4).Number of Arguments: – By default, a function must be called with the correct number of arguments. Meaning that if your function expects 2 arguments, you have to call the function with 2 arguments, not more, and not less. If you try to call the function with 1 or 3 arguments, you will get an error.

5). one can pass functions as parameters in a function

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Classes and Objects in Python (Notes)

Classes and Objects: –
1). Python is an object oriented programming language.Almost everything in Python is an object, with its properties and methods.
A Class is like an object constructor, or a “blueprint” for creating objects.In order to Create a Class use the keyword class.
2). Creating an Object: – example:- Now we can use the class named MyClass to create objects.Create an object named p1, and print the value of x.
3). The __init__() Function: – The examples above are classes and objects in their simplest form, and are not really useful in real life applications.To understand the meaning of classes we have to understand the built-in __init__() function. All classes have a function called __init__(), which is always executed when the class is being initiated. Use the __init__() function to assign values to object properties, or other operations that are necessary to do when the object is being created.
4). The __str__() Function: – The __str__() function controls what should be returned when the class object is represented as a string.
If the __str__() function is not set, the string representation of the object is returned.
5). Object Methods: – Objects can also contain methods. Methods in objects are functions that belong to the object.
6). The self Parameter: – The self parameter is a reference to the current instance of the class, and is used to access variables that belongs to the class. It does not have to be named self , you can call it whatever you like, but it has to be the first parameter of any function in the class.
7). Modify Object Properties: – You can modify properties on objects.
8). Delete Object Properties: – You can delete properties on objects by using the del keyword.
9). Delete Objects: – You can delete objects by using the del keyword,
10). The pass Statement: -class definitions cannot be empty, but if you for some reason have a class definition with no content, put in the pass statement to avoid getting an error.

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Hello world Program (Notes)

 

The Key takeaways are:

1). writing hello world program using PyCharm.

2). How to create a python project and how to edit configurations in PyCharm?

3). How to add interpreter using PyCharm?

4). Creating a new python file in python project and executing the file using Run command.

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Python program to Declare 10 variables and perform arithmetic operations(Exponential, Modulus and Floor Division) on them.

# Declare 10 variables and perform arithmetic operations(Exponential, Modulus and Floor Division) on them.
a=1
b=2
c=3
d=4
e=5
f=6
g=7
h=8
i=9
j=10

#Exponential operation
x=(j**a)
y=(x**b)
print(y)

#Modulus operation
z=(d%c)
print(z)

#floor division
fd=(g//f)
print(fd)

Python program to Declare 10 variables and perform arithmetic operations(Addition,Multiplication,Division) on them.

# Declare 10 variables and perform arithmetic operations(Addition,Multiplication,Division) on them.
a=5
b=10
c=15
d=20
e=25
f=30
g=35
h=40
i=45
j=50
#addition
sum=a+b+c+d+e+f+g+h+i+j
print(sum)

#Multiplication
y=(a*b)
print(y)

#division
z=(j/a)
print(z)


Results:-

Write a code to print a Fibonacci series upto the nth term. Use the int(input()) to get an input from the user as well for the value of n.)

#Write a code to print a Fibonacci series upto the nth term. Use the int(input()) to get an input from the user as well for the value of n.)
x = int(input("enter number of terms in the fibonacci series: "))
def fibonacci1(x):
    n1 = 0
    n2 = 1
    sum1 = 0
    if x <=0:
        print("please enter a number greater than 0")
    else:
        for i in range(0, x):
            print(sum1, end=" ")
            n1 = n2
            n2 = sum1
            sum1 = n1 + n2
fibonacci1(x)

Write a code using a function to check whether a given number is prime number or not

#Write a code using a function to check whether a given number is prime number or not
x= int(input("enter a number: "))
def primeornot(x):
    if x <= 1:
        print("1 is not a prime number ")
    elif x == 2:
        print("2 is a prime number")
    elif x == 3:
        print("3 is a prime number")
    else :
        if x%2 == 0 or x%3 == 0 or x%5 == 0 or x%6 == 0 :
                print("Given number is not a prime number")
        else :
                print(" Given number is a prime number")
primeornot(x)

Program to check whether a given number is even or odd using a function

 

#Write a code using a function to check whether a given number is even or odd

x= int(input("enter a number: "))
def evenorodd(x):
    if x == 0:
        print("0 is neither odd nor even ")
    elif x%2 == 0:
        print("Given number is even ")
    else :
        print("Given number is odd ")

evenorodd(x)
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