Added a python program of Bohr's model and a timer

python/bohrs_model.py

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+'''
+Bohr's model consists of a small nucleus (positively charged) surrounded by negative electrons moving around the nucleus in orbits.
+Bohr found that an electron located away from the nucleus has more energy, and the electron which is closer to nucleus has less energy.
+Postulates of Bohr's Model of an Atom:
+>In an atom, electrons (negatively charged) revolve around the positively charged nucleus in a definite circular path called orbits or shells.
+>Each orbit or shell has a fixed energy and these circular orbits are known as orbital shells.
+
+'''
+
+
+import turtle
+
+
+def pen_jump(pen, x, y):
+    pen.penup()
+    pen.goto(x, y)
+    pen.pendown()
+
+
+def turtle_setup(width=1000, height=1000):
+    turtle.Screen()
+    turtle.setup(width, height)
+    turtle.clearscreen()
+    turtle.title("Bohr (circle) atom")
+
+
+def turtle_pen(shape="circle", speed=10, size=3, colors=("blue", "green")):
+    pen = turtle.Turtle()
+    pen.shape(shape)
+    pen.speed(speed)
+    pen.pensize(size)
+    pen.color(*colors)
+    pen_jump(pen, 0, 0)
+    pen.stamp()
+    return pen
+
+
+def turtle_stop(pen):
+    pen.hideturtle()
+    turtle.exitonclick()
+
+
+def draw_atom(pen, radius, levels, electrons_per_level, electron_size=15, electron_color="red"):
+    full_circle = 360
+    for level in range(levels):
+        r = radius * (level + 1)                           # concentric circles
+        electrons_in_level = electrons_per_level[level]
+        arcs = full_circle / electrons_in_level            # arcs between each electron
+        circumference = 0
+        pen_jump(pen, 0, -r)                               # centering
+        while circumference < full_circle:
+            pen.dot(electron_size, electron_color)
+            pen.circle(r, arcs)
+            circumference = circumference + arcs
+
+
+if __name__ == '__main__':
+    electrons_per_level = []
+    levels = eval(input('How many levels? '))
+    first_level_radius = 45
+
+    for i in range(levels):
+        e = eval(input(f'Electrons in level {str(i + 1)}: '))
+        electrons_per_level.append(e)
+
+    print(electrons_per_level)
+
+    turtle_setup()
+    pen = turtle_pen()
+    draw_atom(pen, first_level_radius, levels, electrons_per_level)
+    turtle_stop(pen)

python/timer.py

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+import time
+# The countdown function is defined below
+
+def countdown(t):
+    while t:
+        mins, secs = divmod(t, 60)
+        timer = '{:02d}:{:02d}'.format(mins, secs)
+        print(timer, end="\r")
+
+        time.sleep(1)
+        t -= 1
+    print('Let\'s go!!')    
+
+
+
+t = input("Enter the time in seconds: ")
+countdown(int(t))
+
+
+