Std 11th | Physics |First Term Examination | Practice Question Paper | Maharashtra State Board|#exam

Niels Bohr a Danish physicist received his PhD from the University of Copenhagen in 1911. He that spent a year with J.J. Thomson and Ernest Rutherford in England. In 1913, he returned to Copenhagen Where he remained for the rest of his life. In 1920 he was named Director of the Institute of theory! Physics After first World War Bohr worked energetically for peaceful uses of atomic energy recieved the first Atoms for Peace award in 1957 Bohr was awarded the Nobel Prize in Physics 1922 (a) The Angular momentum of an electron in a given stationary state can be expressed as m_e vr =h/(2pi) where n=1, 2,3 ...... Thus an electron can move only in those orbits for which its angular momentum is integral multiple of h/2 pi that is why only certain fixed orbits are alowed (b) The radii of the stationary states are expressed as r_n=n^2a_0 where a_0 =52.9 pm. Thus the radius the first stationary state, called the Bohr radius, is 52.9 pm. Normally the electron in the hydrogen atom is found in this orbit (that is n =1). As n increases the value of r will increase (c) The most important property associated with the electron E_n=-2.18xx10^(-18)(Z^2/n^2)J n=1,2,3 (d)it is also possible to calculate to calculate the velocities of electrons moving in these orbits by using v_n=2.18 10^6xxZ/n m/sec. Qualitatively the magnitude of velocity of electron increases with increase of positive charge on the nucleus and decreases with increases the value of n. (e)Bohr's theory can also be applied to th ions containing only one electron, similar to that present it hydrogen atom. For example , He^+ Li^(2+) , Be^(3+) and so on. given by the expression Ex=-218x n=1,2,3 (d) It is also possible to calculate the velocities of electrons moving in these orbits by using V 2.1810 cm/sec Qualitatively the magnitude of velocity of electron increases with increase of positive charge on the nucleus and decreases with increase the value of n (e) Bohr's theory can also be applied to the ions containing only one electron, similar to that presenti hydrogen atom For example, Help, Be and so on Choose the correct statement

Niels Bohr a Danish physicist received his PhD from the University of Copenhagen in 1911. He that spent a year with J.J. Thomson and Ernest Rutherford in England. In 1913, he returned to Copenhagen Where he remained for the rest of his life. In 1920 he was named Director of the Institute of theory! Physics After first World War Bohr worked energetically for peaceful uses of atomic energy recieved the first Atoms for Peace award in 1957 Bohr was awarded the Nobel Prize in Physics 1922 (a) The Angular momentum of an electron in a given stationary state can be expressed as m_e vr =h/(2pi) where n=1, 2,3 ...... Thus an electron can move only in those orbits for which its angular momentum is integral multiple of h/2 pi that is why only certain fixed orbits are alowed (b) The radii of the stationary states are expressed as r_n=n^2a_0 where a_0 =52.9 pm. Thus the radius the first stationary state, called the Bohr radius, is 52.9 pm. Normally the electron in the hydrogen atom is found in this orbit (that is n =1). As n increases the value of r will increase (c) The most important property associated with the electron E_n=-2.18xx10^(-18)(Z^2/n^2)J n=1,2,3 (d)it is also possible to calculate to calculate the velocities of electrons moving in these orbits by using v_n=2.18 10^6xxZ/n m/sec. Qualitatively the magnitude of velocity of electron increases with increase of positive charge on the nucleus and decreases with increases the value of n. (e)Bohr's theory can also be applied to th ions containing only one electron, similar to that present it hydrogen atom. For example , He^+ Li^(2+) , Be^(3+) and so on. given by the expression Ex=-218x n=1,2,3 (d) It is also possible to calculate the velocities of electrons moving in these orbits by using V 2.1810 cm/sec Qualitatively the magnitude of velocity of electron increases with increase of positive charge on the nucleus and decreases with increase the value of n (e) Bohr's theory can also be applied to the ions containing only one electron, similar to that presenti hydrogen atom For example, Help, Be and so on Choose the incorrect curve : if v=velocity of electron in Bohr's orbit r=Radius of electron in Bohr's orbit P.E.=Potential energy of electron in Bohr's orbit K.E.=Kinetic energy of the electron in Bohr's orbit.

The ratio of the 11th term to the 18th term of an AP is 2 : 3 . Find the ratio of the 5th term to the 21st term and also the ratio of the sum of the first five terms to the sum of the first 21 terms.