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Page 1 29. Modern Physics I Introductory Exercise 29.1 1. The po si tron has same mass m as the elec tron. The reduced mass of elec tron po si tron atom is m = ´ + = m m m m 1 2 m R m e c h H = 4 0 2 3 8 e Þ R R P H = 2 1 1 2 1 3 2 2 l H H R = - æ è ç ö ø ÷ 1 1 2 1 3 2 2 l P P R = - æ è ç ö ø ÷ Þ l l P H H P R R = = 2 Þ l l p H = = ´ 2 2 6563 Å = 13126 Å = 1.31 m m 1 1 2 1 3 2 2 2 l He = - æ è ç ö ø ÷ × R z H Þ 1 1 2 l l He H = × z Þ l l He H Å = = 2 6563 2 2 2 Þ l He nm = 164 2. 1 1 2 1 2 2 l = - é ë ê ù û ú R n for larg est wave length n = 3 Þ 1 1 4 1 9 l = - é ë ê ù û ú R Þ l = = ´ ´ 36 5 36 5 10 7 R 1.097 Þ l = 656 nm 3. For H-atom r n h me n = e p 0 2 2 2 u e nh n = e 2 0 2 T r u n h nh me e n n n = = ´ ´ 2 2 2 2 2 0 2 2 p p e e p 0 = 4 0 3 3 4 e n h me r T me n h n n = = 1 4 4 0 2 3 3 e Þ r me h 1 4 0 2 3 4 = e Þ n 1 31 19 4 12 2 3 10 1 6 10 4 10 10 = ´ ´ ´ ´ ´ ´ ´ - - - - 9.1 8.85 6.6 ( . ) ( ) ( 4 3 ) Þ n 1 15 1 0 = ´ 6.58 Hz n n n 2 1 3 1 15 2 8 10 8 = = = ´ 6.58 = ´ 0.823 10 15 Hz (b) 1 1 1 1 2 2 2 l = - é ë ê ù û ú R Þ n l = = ´ ´ é ë ê ù û ú c R 3 10 3 4 8 Þ n = ´ ´ ´ 9 10 10 4 8 7 1.097 = ´ 2.46 Hz 10 15 (c) Number of revolutions = ´ = ´ ´ ´ - v T 2 15 8 10 1 10 0.823 = ´ 8.23 10 6 revolution Page 2 29. Modern Physics I Introductory Exercise 29.1 1. The po si tron has same mass m as the elec tron. The reduced mass of elec tron po si tron atom is m = ´ + = m m m m 1 2 m R m e c h H = 4 0 2 3 8 e Þ R R P H = 2 1 1 2 1 3 2 2 l H H R = - æ è ç ö ø ÷ 1 1 2 1 3 2 2 l P P R = - æ è ç ö ø ÷ Þ l l P H H P R R = = 2 Þ l l p H = = ´ 2 2 6563 Å = 13126 Å = 1.31 m m 1 1 2 1 3 2 2 2 l He = - æ è ç ö ø ÷ × R z H Þ 1 1 2 l l He H = × z Þ l l He H Å = = 2 6563 2 2 2 Þ l He nm = 164 2. 1 1 2 1 2 2 l = - é ë ê ù û ú R n for larg est wave length n = 3 Þ 1 1 4 1 9 l = - é ë ê ù û ú R Þ l = = ´ ´ 36 5 36 5 10 7 R 1.097 Þ l = 656 nm 3. For H-atom r n h me n = e p 0 2 2 2 u e nh n = e 2 0 2 T r u n h nh me e n n n = = ´ ´ 2 2 2 2 2 0 2 2 p p e e p 0 = 4 0 3 3 4 e n h me r T me n h n n = = 1 4 4 0 2 3 3 e Þ r me h 1 4 0 2 3 4 = e Þ n 1 31 19 4 12 2 3 10 1 6 10 4 10 10 = ´ ´ ´ ´ ´ ´ ´ - - - - 9.1 8.85 6.6 ( . ) ( ) ( 4 3 ) Þ n 1 15 1 0 = ´ 6.58 Hz n n n 2 1 3 1 15 2 8 10 8 = = = ´ 6.58 = ´ 0.823 10 15 Hz (b) 1 1 1 1 2 2 2 l = - é ë ê ù û ú R Þ n l = = ´ ´ é ë ê ù û ú c R 3 10 3 4 8 Þ n = ´ ´ ´ 9 10 10 4 8 7 1.097 = ´ 2.46 Hz 10 15 (c) Number of revolutions = ´ = ´ ´ ´ - v T 2 15 8 10 1 10 0.823 = ´ 8.23 10 6 revolution 4.Reduce mass = + = ´ + = mm mm p p m m 2071836 2071836 186 mm mm () m r h e h me 10 2 22 0 2 22 4 4 4 4 = æ è ç ç ö ø ÷ ÷ = æ è ç ç ö ø ÷ ÷ pe pm pe p()186 Putting the value we get r 1 13 10 = ´ - 2.55 m E e h 1 4 0 2 2 8 2810 = - = - m e eV Ionization energy = - = E 1 2.81 keV 5. (a) l = = ´ ´ ´ = ´ - - - h mv 6.6 4.8 m 10 46 10 30 10 34 3 34 (b) l = ´ ´ ´ = ´ - - - 6.6 9.1 7.3 10 m 11 10 10 10 3 4 31 7 6. (a) After absorbing 12.3 eV the atom excited to n = 3 state 1 1 1 2 l L R n = - é ë ê ù û ú 1 1 1 9 8 9 1 l L R R = - é ë ê ù û ú = Þ l L R 1 9 8 9 8 10 102 7 = = ´ ´ = 1.097 nm 1 1 1 4 2 l L R = - é ë ê ù û ú Þ l L R 2 4 3 4 3 10 7 = = ´ ´ = 1.097 122 nm 1 1 2 1 3 5 36 2 2 l B R R = - é ë ê ù û ú = Þ l B R = 36 5 Þ l B = ´ ´ = 36 5 10 7 1.097 653 nm 7. n n n b a a K K L = + Þ l l l l l a a b a b L K K K K = ´ - c c c K K L l l l b a a = + Þ l a L = ´ - 0.71 0.63 0.71 0.63 Þ 1 1 1 l l l a b a L K K = - l a L = 5.59 nm 8. l = hc E D Þ l a K E = ´ ´ ´ - ´ ´ - - 6.6 1.6 10 3 10 2870 10 34 8 1 19 ( ) Þ 0.71 6.6 1.6 ´ = ´ ´ ´ - ´ ´ - - - 10 10 3 10 2870 10 9 34 8 1 19 ( ) E Solving this we get E 1 4613 = - eV l K B E = ´ ´ ´ - ´ ´ = - - 6.6 1.6 0.63 10 3 10 4613 10 34 8 3 19 ( ) Solving this we get E 3 2650 = - eV 9. n 31 4 = = E h f …(i) n 21 3 3 4 4 3 4 = = æ è ç ö ø ÷ = E h E h f n 32 4 = = E h f 60 E 3 K a K b E = – 2870 eV 2 E 1 5 E E 4 E 1 2 3 n = 3 n = 2 n = 1 Page 3 29. Modern Physics I Introductory Exercise 29.1 1. The po si tron has same mass m as the elec tron. The reduced mass of elec tron po si tron atom is m = ´ + = m m m m 1 2 m R m e c h H = 4 0 2 3 8 e Þ R R P H = 2 1 1 2 1 3 2 2 l H H R = - æ è ç ö ø ÷ 1 1 2 1 3 2 2 l P P R = - æ è ç ö ø ÷ Þ l l P H H P R R = = 2 Þ l l p H = = ´ 2 2 6563 Å = 13126 Å = 1.31 m m 1 1 2 1 3 2 2 2 l He = - æ è ç ö ø ÷ × R z H Þ 1 1 2 l l He H = × z Þ l l He H Å = = 2 6563 2 2 2 Þ l He nm = 164 2. 1 1 2 1 2 2 l = - é ë ê ù û ú R n for larg est wave length n = 3 Þ 1 1 4 1 9 l = - é ë ê ù û ú R Þ l = = ´ ´ 36 5 36 5 10 7 R 1.097 Þ l = 656 nm 3. For H-atom r n h me n = e p 0 2 2 2 u e nh n = e 2 0 2 T r u n h nh me e n n n = = ´ ´ 2 2 2 2 2 0 2 2 p p e e p 0 = 4 0 3 3 4 e n h me r T me n h n n = = 1 4 4 0 2 3 3 e Þ r me h 1 4 0 2 3 4 = e Þ n 1 31 19 4 12 2 3 10 1 6 10 4 10 10 = ´ ´ ´ ´ ´ ´ ´ - - - - 9.1 8.85 6.6 ( . ) ( ) ( 4 3 ) Þ n 1 15 1 0 = ´ 6.58 Hz n n n 2 1 3 1 15 2 8 10 8 = = = ´ 6.58 = ´ 0.823 10 15 Hz (b) 1 1 1 1 2 2 2 l = - é ë ê ù û ú R Þ n l = = ´ ´ é ë ê ù û ú c R 3 10 3 4 8 Þ n = ´ ´ ´ 9 10 10 4 8 7 1.097 = ´ 2.46 Hz 10 15 (c) Number of revolutions = ´ = ´ ´ ´ - v T 2 15 8 10 1 10 0.823 = ´ 8.23 10 6 revolution 4.Reduce mass = + = ´ + = mm mm p p m m 2071836 2071836 186 mm mm () m r h e h me 10 2 22 0 2 22 4 4 4 4 = æ è ç ç ö ø ÷ ÷ = æ è ç ç ö ø ÷ ÷ pe pm pe p()186 Putting the value we get r 1 13 10 = ´ - 2.55 m E e h 1 4 0 2 2 8 2810 = - = - m e eV Ionization energy = - = E 1 2.81 keV 5. (a) l = = ´ ´ ´ = ´ - - - h mv 6.6 4.8 m 10 46 10 30 10 34 3 34 (b) l = ´ ´ ´ = ´ - - - 6.6 9.1 7.3 10 m 11 10 10 10 3 4 31 7 6. (a) After absorbing 12.3 eV the atom excited to n = 3 state 1 1 1 2 l L R n = - é ë ê ù û ú 1 1 1 9 8 9 1 l L R R = - é ë ê ù û ú = Þ l L R 1 9 8 9 8 10 102 7 = = ´ ´ = 1.097 nm 1 1 1 4 2 l L R = - é ë ê ù û ú Þ l L R 2 4 3 4 3 10 7 = = ´ ´ = 1.097 122 nm 1 1 2 1 3 5 36 2 2 l B R R = - é ë ê ù û ú = Þ l B R = 36 5 Þ l B = ´ ´ = 36 5 10 7 1.097 653 nm 7. n n n b a a K K L = + Þ l l l l l a a b a b L K K K K = ´ - c c c K K L l l l b a a = + Þ l a L = ´ - 0.71 0.63 0.71 0.63 Þ 1 1 1 l l l a b a L K K = - l a L = 5.59 nm 8. l = hc E D Þ l a K E = ´ ´ ´ - ´ ´ - - 6.6 1.6 10 3 10 2870 10 34 8 1 19 ( ) Þ 0.71 6.6 1.6 ´ = ´ ´ ´ - ´ ´ - - - 10 10 3 10 2870 10 9 34 8 1 19 ( ) E Solving this we get E 1 4613 = - eV l K B E = ´ ´ ´ - ´ ´ = - - 6.6 1.6 0.63 10 3 10 4613 10 34 8 3 19 ( ) Solving this we get E 3 2650 = - eV 9. n 31 4 = = E h f …(i) n 21 3 3 4 4 3 4 = = æ è ç ö ø ÷ = E h E h f n 32 4 = = E h f 60 E 3 K a K b E = – 2870 eV 2 E 1 5 E E 4 E 1 2 3 n = 3 n = 2 n = 1 Introductory Exercise 29.2 1. eV hc W 0 = - l Þ eV 0 34 8 7 19 10 3 10 2 10 10 = ´ ´ ´ ´ ´ ´ - - - - 6.6 1.6 4.3eV Þ eV 0 = - = 6.2eV 4.3eV 1.9eV Þ V 0 =1.9 volt 2.P=1.5mW = ´ - 1.5 W 10 3 Energy of each photon = ´ ´ ´ ´ - - 6.62 10 3 10 4 10 34 8 7 = ´ - 4.96 10 19 J Number of photons incident per second = = ´ ´ - - P Energy of each photon 1.5 4.96 10 10 3 19 ~ - ´ 3 10 15 The number of photoelectrons produce = ´ ´ 0.1% 3 10 15 = ´ 3 10 12 Current i = ´ ´ ´ - 3 10 10 12 19 1.6 A = ´ - 4.8 A 10 7 = 0.48 A m 3. K hf W hf hf max = - = - 0 Þ K f f max ( ) µ - 0 4. K hc W max = - l = ´ ´ ´ ´ ´ ´ - é ë ê ù û ú - - - 6.62 1.6 eV 10 3 10 2 10 10 3 34 8 7 19 = - = [ ] 6.20 eV 3.20 eV 3 The minimum kinetic energy = 0. 5. K h f f max [ ] = - 0 1.2 eV = - h f f [ ] 0 …(i) 4.2 eV 1.5 = - h f f [ ] 0 …(ii) Dividing Eq. (i) and Eq. (ii) 124 42 0 0 = - - f f f f 1.5 Þ 3 2 7 7 0 0 f f f f - = - Þ 5 4 0 f f = Þ f f f 0 4 5 = = 0.8 Þ 1.2 1.6 6.62 0.8 ´ ´ = ´ - é ë ê ù û ú - - 10 10 19 34 0 0 f f Þ 1.2 1.6 6.62 ´ ´ ´ = = - - 10 10 2 8 4 19 34 0 0 f f Þ f 0 15 10 = ´ 1.16 Hz Subjective Questions (Level I) 1. Here l = = ´ - 280 28 10 8 nm m E hc = = ´ ´ ´ ´ - - l 6.6 J 10 3 10 28 10 34 8 8 E = ´ ´ = ´ - - 19.8 J J 10 10 28 198 10 28 34 16 19 E = ´ ´ ´ = ´ - - - 198 10 28 10 198 28 19 19 1.6 eV 1.6 4.6 eV ~ We have E mc = 2 Þ m E c = = ´ ´ ´ - 2 19 16 198 10 28 9 10 Þ m = ´ - 8.2 kg 10 36 Momentum p mc = = ´ ´ ´ - 8.2 10 3 10 36 8 = ´ - 2.46 kg-m/s 10 27 2. Intensity of light at a dis tance 2 m From the source = ´ = 1 4 2 1 16 2 2 p p ( ) / W m 61 Page 4 29. Modern Physics I Introductory Exercise 29.1 1. The po si tron has same mass m as the elec tron. The reduced mass of elec tron po si tron atom is m = ´ + = m m m m 1 2 m R m e c h H = 4 0 2 3 8 e Þ R R P H = 2 1 1 2 1 3 2 2 l H H R = - æ è ç ö ø ÷ 1 1 2 1 3 2 2 l P P R = - æ è ç ö ø ÷ Þ l l P H H P R R = = 2 Þ l l p H = = ´ 2 2 6563 Å = 13126 Å = 1.31 m m 1 1 2 1 3 2 2 2 l He = - æ è ç ö ø ÷ × R z H Þ 1 1 2 l l He H = × z Þ l l He H Å = = 2 6563 2 2 2 Þ l He nm = 164 2. 1 1 2 1 2 2 l = - é ë ê ù û ú R n for larg est wave length n = 3 Þ 1 1 4 1 9 l = - é ë ê ù û ú R Þ l = = ´ ´ 36 5 36 5 10 7 R 1.097 Þ l = 656 nm 3. For H-atom r n h me n = e p 0 2 2 2 u e nh n = e 2 0 2 T r u n h nh me e n n n = = ´ ´ 2 2 2 2 2 0 2 2 p p e e p 0 = 4 0 3 3 4 e n h me r T me n h n n = = 1 4 4 0 2 3 3 e Þ r me h 1 4 0 2 3 4 = e Þ n 1 31 19 4 12 2 3 10 1 6 10 4 10 10 = ´ ´ ´ ´ ´ ´ ´ - - - - 9.1 8.85 6.6 ( . ) ( ) ( 4 3 ) Þ n 1 15 1 0 = ´ 6.58 Hz n n n 2 1 3 1 15 2 8 10 8 = = = ´ 6.58 = ´ 0.823 10 15 Hz (b) 1 1 1 1 2 2 2 l = - é ë ê ù û ú R Þ n l = = ´ ´ é ë ê ù û ú c R 3 10 3 4 8 Þ n = ´ ´ ´ 9 10 10 4 8 7 1.097 = ´ 2.46 Hz 10 15 (c) Number of revolutions = ´ = ´ ´ ´ - v T 2 15 8 10 1 10 0.823 = ´ 8.23 10 6 revolution 4.Reduce mass = + = ´ + = mm mm p p m m 2071836 2071836 186 mm mm () m r h e h me 10 2 22 0 2 22 4 4 4 4 = æ è ç ç ö ø ÷ ÷ = æ è ç ç ö ø ÷ ÷ pe pm pe p()186 Putting the value we get r 1 13 10 = ´ - 2.55 m E e h 1 4 0 2 2 8 2810 = - = - m e eV Ionization energy = - = E 1 2.81 keV 5. (a) l = = ´ ´ ´ = ´ - - - h mv 6.6 4.8 m 10 46 10 30 10 34 3 34 (b) l = ´ ´ ´ = ´ - - - 6.6 9.1 7.3 10 m 11 10 10 10 3 4 31 7 6. (a) After absorbing 12.3 eV the atom excited to n = 3 state 1 1 1 2 l L R n = - é ë ê ù û ú 1 1 1 9 8 9 1 l L R R = - é ë ê ù û ú = Þ l L R 1 9 8 9 8 10 102 7 = = ´ ´ = 1.097 nm 1 1 1 4 2 l L R = - é ë ê ù û ú Þ l L R 2 4 3 4 3 10 7 = = ´ ´ = 1.097 122 nm 1 1 2 1 3 5 36 2 2 l B R R = - é ë ê ù û ú = Þ l B R = 36 5 Þ l B = ´ ´ = 36 5 10 7 1.097 653 nm 7. n n n b a a K K L = + Þ l l l l l a a b a b L K K K K = ´ - c c c K K L l l l b a a = + Þ l a L = ´ - 0.71 0.63 0.71 0.63 Þ 1 1 1 l l l a b a L K K = - l a L = 5.59 nm 8. l = hc E D Þ l a K E = ´ ´ ´ - ´ ´ - - 6.6 1.6 10 3 10 2870 10 34 8 1 19 ( ) Þ 0.71 6.6 1.6 ´ = ´ ´ ´ - ´ ´ - - - 10 10 3 10 2870 10 9 34 8 1 19 ( ) E Solving this we get E 1 4613 = - eV l K B E = ´ ´ ´ - ´ ´ = - - 6.6 1.6 0.63 10 3 10 4613 10 34 8 3 19 ( ) Solving this we get E 3 2650 = - eV 9. n 31 4 = = E h f …(i) n 21 3 3 4 4 3 4 = = æ è ç ö ø ÷ = E h E h f n 32 4 = = E h f 60 E 3 K a K b E = – 2870 eV 2 E 1 5 E E 4 E 1 2 3 n = 3 n = 2 n = 1 Introductory Exercise 29.2 1. eV hc W 0 = - l Þ eV 0 34 8 7 19 10 3 10 2 10 10 = ´ ´ ´ ´ ´ ´ - - - - 6.6 1.6 4.3eV Þ eV 0 = - = 6.2eV 4.3eV 1.9eV Þ V 0 =1.9 volt 2.P=1.5mW = ´ - 1.5 W 10 3 Energy of each photon = ´ ´ ´ ´ - - 6.62 10 3 10 4 10 34 8 7 = ´ - 4.96 10 19 J Number of photons incident per second = = ´ ´ - - P Energy of each photon 1.5 4.96 10 10 3 19 ~ - ´ 3 10 15 The number of photoelectrons produce = ´ ´ 0.1% 3 10 15 = ´ 3 10 12 Current i = ´ ´ ´ - 3 10 10 12 19 1.6 A = ´ - 4.8 A 10 7 = 0.48 A m 3. K hf W hf hf max = - = - 0 Þ K f f max ( ) µ - 0 4. K hc W max = - l = ´ ´ ´ ´ ´ ´ - é ë ê ù û ú - - - 6.62 1.6 eV 10 3 10 2 10 10 3 34 8 7 19 = - = [ ] 6.20 eV 3.20 eV 3 The minimum kinetic energy = 0. 5. K h f f max [ ] = - 0 1.2 eV = - h f f [ ] 0 …(i) 4.2 eV 1.5 = - h f f [ ] 0 …(ii) Dividing Eq. (i) and Eq. (ii) 124 42 0 0 = - - f f f f 1.5 Þ 3 2 7 7 0 0 f f f f - = - Þ 5 4 0 f f = Þ f f f 0 4 5 = = 0.8 Þ 1.2 1.6 6.62 0.8 ´ ´ = ´ - é ë ê ù û ú - - 10 10 19 34 0 0 f f Þ 1.2 1.6 6.62 ´ ´ ´ = = - - 10 10 2 8 4 19 34 0 0 f f Þ f 0 15 10 = ´ 1.16 Hz Subjective Questions (Level I) 1. Here l = = ´ - 280 28 10 8 nm m E hc = = ´ ´ ´ ´ - - l 6.6 J 10 3 10 28 10 34 8 8 E = ´ ´ = ´ - - 19.8 J J 10 10 28 198 10 28 34 16 19 E = ´ ´ ´ = ´ - - - 198 10 28 10 198 28 19 19 1.6 eV 1.6 4.6 eV ~ We have E mc = 2 Þ m E c = = ´ ´ ´ - 2 19 16 198 10 28 9 10 Þ m = ´ - 8.2 kg 10 36 Momentum p mc = = ´ ´ ´ - 8.2 10 3 10 36 8 = ´ - 2.46 kg-m/s 10 27 2. Intensity of light at a dis tance 2 m From the source = ´ = 1 4 2 1 16 2 2 p p ( ) / W m 61 Let plate area is A Energy incident on unit time is E A 1 1 16 = p w Energy of each photon = ´ ´ ´ ´ - - 6.6 4.8 10 3 10 10 34 8 7 Number of photons striking per unit area n A A A = ´ ´ ´ ´ ´ ´ ´ ´ - - 1 16 10 10 3 10 7 34 8 p 4.8 6.6 = ´ 4.82 10 16 per m 2 s 3. Here p = ´ - 8.24 kg-m/s 10 28 (a) Energy of photon E pc = Þ E = ´ ´ ´ - 8.24 10 3 10 28 8 Þ E = ´ - 2.47 J 10 19 Energy in eV in joule 1.6 = ´ - E 10 19 = ´ ´ - - 2.47 1.6 10 10 19 19 Energy (in eV) = 1.54 eV (b) Wavelength l = = ´ ´ = - - h p 6.6 8.24 nm 10 10 804 34 28 This wavelength in Infrared region. 4. We have c f = l Þ f c = = ´ ´ - l 3 10 6 10 8 7 m/s m Þ f = ´ 5 10 14 Hz We have p E t = Þ E pt = power per sec = energy Þ P E = Þ 75 = ´ ´ ( ) h v n Þ = ´ ´ ´ - 75 10 5 10 34 14 6.6 Þ n = ´ 2.3 10 20 photons/sec 5. (a) E = = ´ ´ ´ - 2.45 MeV 2.45 1.6 10 J 19 6 10 E h = n Þ n = = ´ ´ - - E h 3.92 6.6 10 10 13 34 Þ n = ´ 5.92 Hz 10 20 (b) We have c = nl Þ l n = c Þ l = ´ ´ = ´ - 3 10 10 8 20 5.92 5.06 10 m 13 6. We have p mK = 2 Þ p mK 1 1 2 = and p mK 2 2 2 = Þ p p K K 1 2 1 2 = Þ 1 2 1 2 = K K [ ] Q p p 2 1 2 = Þ K K 2 1 4 = (b) E p c 1 1 = and E p c 2 2 = Þ E p c 2 1 2 = Þ E E 2 1 2 = 7. (a) Since power = energy per unit line let n be the number of photons Þ P nE = Þ 10 = ´ n nc l Þ n hc = ´ = ´ ´ ´ ´ ´ - - 10 10 500 10 10 3 10 9 34 8 l 6.6 Þ n = ´ 2.52 10 19 (b) Force exerted on that surface F P c = = ´ = ´ - 10 3 10 8 3.33 10 N 8 8. Absorbing (power) light =70% of in ci dent light Þ P a =70% of 10 7 W W = Refractive power = 30% of 10 W Þ P R = 3 W The force exerted = + P c P c a R 2 = + ´ = ´ 7 2 3 13 3 10 8 c = ´ - 4.3 N 10 8 62 Page 5 29. Modern Physics I Introductory Exercise 29.1 1. The po si tron has same mass m as the elec tron. The reduced mass of elec tron po si tron atom is m = ´ + = m m m m 1 2 m R m e c h H = 4 0 2 3 8 e Þ R R P H = 2 1 1 2 1 3 2 2 l H H R = - æ è ç ö ø ÷ 1 1 2 1 3 2 2 l P P R = - æ è ç ö ø ÷ Þ l l P H H P R R = = 2 Þ l l p H = = ´ 2 2 6563 Å = 13126 Å = 1.31 m m 1 1 2 1 3 2 2 2 l He = - æ è ç ö ø ÷ × R z H Þ 1 1 2 l l He H = × z Þ l l He H Å = = 2 6563 2 2 2 Þ l He nm = 164 2. 1 1 2 1 2 2 l = - é ë ê ù û ú R n for larg est wave length n = 3 Þ 1 1 4 1 9 l = - é ë ê ù û ú R Þ l = = ´ ´ 36 5 36 5 10 7 R 1.097 Þ l = 656 nm 3. For H-atom r n h me n = e p 0 2 2 2 u e nh n = e 2 0 2 T r u n h nh me e n n n = = ´ ´ 2 2 2 2 2 0 2 2 p p e e p 0 = 4 0 3 3 4 e n h me r T me n h n n = = 1 4 4 0 2 3 3 e Þ r me h 1 4 0 2 3 4 = e Þ n 1 31 19 4 12 2 3 10 1 6 10 4 10 10 = ´ ´ ´ ´ ´ ´ ´ - - - - 9.1 8.85 6.6 ( . ) ( ) ( 4 3 ) Þ n 1 15 1 0 = ´ 6.58 Hz n n n 2 1 3 1 15 2 8 10 8 = = = ´ 6.58 = ´ 0.823 10 15 Hz (b) 1 1 1 1 2 2 2 l = - é ë ê ù û ú R Þ n l = = ´ ´ é ë ê ù û ú c R 3 10 3 4 8 Þ n = ´ ´ ´ 9 10 10 4 8 7 1.097 = ´ 2.46 Hz 10 15 (c) Number of revolutions = ´ = ´ ´ ´ - v T 2 15 8 10 1 10 0.823 = ´ 8.23 10 6 revolution 4.Reduce mass = + = ´ + = mm mm p p m m 2071836 2071836 186 mm mm () m r h e h me 10 2 22 0 2 22 4 4 4 4 = æ è ç ç ö ø ÷ ÷ = æ è ç ç ö ø ÷ ÷ pe pm pe p()186 Putting the value we get r 1 13 10 = ´ - 2.55 m E e h 1 4 0 2 2 8 2810 = - = - m e eV Ionization energy = - = E 1 2.81 keV 5. (a) l = = ´ ´ ´ = ´ - - - h mv 6.6 4.8 m 10 46 10 30 10 34 3 34 (b) l = ´ ´ ´ = ´ - - - 6.6 9.1 7.3 10 m 11 10 10 10 3 4 31 7 6. (a) After absorbing 12.3 eV the atom excited to n = 3 state 1 1 1 2 l L R n = - é ë ê ù û ú 1 1 1 9 8 9 1 l L R R = - é ë ê ù û ú = Þ l L R 1 9 8 9 8 10 102 7 = = ´ ´ = 1.097 nm 1 1 1 4 2 l L R = - é ë ê ù û ú Þ l L R 2 4 3 4 3 10 7 = = ´ ´ = 1.097 122 nm 1 1 2 1 3 5 36 2 2 l B R R = - é ë ê ù û ú = Þ l B R = 36 5 Þ l B = ´ ´ = 36 5 10 7 1.097 653 nm 7. n n n b a a K K L = + Þ l l l l l a a b a b L K K K K = ´ - c c c K K L l l l b a a = + Þ l a L = ´ - 0.71 0.63 0.71 0.63 Þ 1 1 1 l l l a b a L K K = - l a L = 5.59 nm 8. l = hc E D Þ l a K E = ´ ´ ´ - ´ ´ - - 6.6 1.6 10 3 10 2870 10 34 8 1 19 ( ) Þ 0.71 6.6 1.6 ´ = ´ ´ ´ - ´ ´ - - - 10 10 3 10 2870 10 9 34 8 1 19 ( ) E Solving this we get E 1 4613 = - eV l K B E = ´ ´ ´ - ´ ´ = - - 6.6 1.6 0.63 10 3 10 4613 10 34 8 3 19 ( ) Solving this we get E 3 2650 = - eV 9. n 31 4 = = E h f …(i) n 21 3 3 4 4 3 4 = = æ è ç ö ø ÷ = E h E h f n 32 4 = = E h f 60 E 3 K a K b E = – 2870 eV 2 E 1 5 E E 4 E 1 2 3 n = 3 n = 2 n = 1 Introductory Exercise 29.2 1. eV hc W 0 = - l Þ eV 0 34 8 7 19 10 3 10 2 10 10 = ´ ´ ´ ´ ´ ´ - - - - 6.6 1.6 4.3eV Þ eV 0 = - = 6.2eV 4.3eV 1.9eV Þ V 0 =1.9 volt 2.P=1.5mW = ´ - 1.5 W 10 3 Energy of each photon = ´ ´ ´ ´ - - 6.62 10 3 10 4 10 34 8 7 = ´ - 4.96 10 19 J Number of photons incident per second = = ´ ´ - - P Energy of each photon 1.5 4.96 10 10 3 19 ~ - ´ 3 10 15 The number of photoelectrons produce = ´ ´ 0.1% 3 10 15 = ´ 3 10 12 Current i = ´ ´ ´ - 3 10 10 12 19 1.6 A = ´ - 4.8 A 10 7 = 0.48 A m 3. K hf W hf hf max = - = - 0 Þ K f f max ( ) µ - 0 4. K hc W max = - l = ´ ´ ´ ´ ´ ´ - é ë ê ù û ú - - - 6.62 1.6 eV 10 3 10 2 10 10 3 34 8 7 19 = - = [ ] 6.20 eV 3.20 eV 3 The minimum kinetic energy = 0. 5. K h f f max [ ] = - 0 1.2 eV = - h f f [ ] 0 …(i) 4.2 eV 1.5 = - h f f [ ] 0 …(ii) Dividing Eq. (i) and Eq. (ii) 124 42 0 0 = - - f f f f 1.5 Þ 3 2 7 7 0 0 f f f f - = - Þ 5 4 0 f f = Þ f f f 0 4 5 = = 0.8 Þ 1.2 1.6 6.62 0.8 ´ ´ = ´ - é ë ê ù û ú - - 10 10 19 34 0 0 f f Þ 1.2 1.6 6.62 ´ ´ ´ = = - - 10 10 2 8 4 19 34 0 0 f f Þ f 0 15 10 = ´ 1.16 Hz Subjective Questions (Level I) 1. Here l = = ´ - 280 28 10 8 nm m E hc = = ´ ´ ´ ´ - - l 6.6 J 10 3 10 28 10 34 8 8 E = ´ ´ = ´ - - 19.8 J J 10 10 28 198 10 28 34 16 19 E = ´ ´ ´ = ´ - - - 198 10 28 10 198 28 19 19 1.6 eV 1.6 4.6 eV ~ We have E mc = 2 Þ m E c = = ´ ´ ´ - 2 19 16 198 10 28 9 10 Þ m = ´ - 8.2 kg 10 36 Momentum p mc = = ´ ´ ´ - 8.2 10 3 10 36 8 = ´ - 2.46 kg-m/s 10 27 2. Intensity of light at a dis tance 2 m From the source = ´ = 1 4 2 1 16 2 2 p p ( ) / W m 61 Let plate area is A Energy incident on unit time is E A 1 1 16 = p w Energy of each photon = ´ ´ ´ ´ - - 6.6 4.8 10 3 10 10 34 8 7 Number of photons striking per unit area n A A A = ´ ´ ´ ´ ´ ´ ´ ´ - - 1 16 10 10 3 10 7 34 8 p 4.8 6.6 = ´ 4.82 10 16 per m 2 s 3. Here p = ´ - 8.24 kg-m/s 10 28 (a) Energy of photon E pc = Þ E = ´ ´ ´ - 8.24 10 3 10 28 8 Þ E = ´ - 2.47 J 10 19 Energy in eV in joule 1.6 = ´ - E 10 19 = ´ ´ - - 2.47 1.6 10 10 19 19 Energy (in eV) = 1.54 eV (b) Wavelength l = = ´ ´ = - - h p 6.6 8.24 nm 10 10 804 34 28 This wavelength in Infrared region. 4. We have c f = l Þ f c = = ´ ´ - l 3 10 6 10 8 7 m/s m Þ f = ´ 5 10 14 Hz We have p E t = Þ E pt = power per sec = energy Þ P E = Þ 75 = ´ ´ ( ) h v n Þ = ´ ´ ´ - 75 10 5 10 34 14 6.6 Þ n = ´ 2.3 10 20 photons/sec 5. (a) E = = ´ ´ ´ - 2.45 MeV 2.45 1.6 10 J 19 6 10 E h = n Þ n = = ´ ´ - - E h 3.92 6.6 10 10 13 34 Þ n = ´ 5.92 Hz 10 20 (b) We have c = nl Þ l n = c Þ l = ´ ´ = ´ - 3 10 10 8 20 5.92 5.06 10 m 13 6. We have p mK = 2 Þ p mK 1 1 2 = and p mK 2 2 2 = Þ p p K K 1 2 1 2 = Þ 1 2 1 2 = K K [ ] Q p p 2 1 2 = Þ K K 2 1 4 = (b) E p c 1 1 = and E p c 2 2 = Þ E p c 2 1 2 = Þ E E 2 1 2 = 7. (a) Since power = energy per unit line let n be the number of photons Þ P nE = Þ 10 = ´ n nc l Þ n hc = ´ = ´ ´ ´ ´ ´ - - 10 10 500 10 10 3 10 9 34 8 l 6.6 Þ n = ´ 2.52 10 19 (b) Force exerted on that surface F P c = = ´ = ´ - 10 3 10 8 3.33 10 N 8 8. Absorbing (power) light =70% of in ci dent light Þ P a =70% of 10 7 W W = Refractive power = 30% of 10 W Þ P R = 3 W The force exerted = + P c P c a R 2 = + ´ = ´ 7 2 3 13 3 10 8 c = ´ - 4.3 N 10 8 62 9. Force = rate of change of mo men tum F p t = D D here Dt = 1 s F p = ° 2 60 cos F p = Þ F nh = l where n is number of photons striking per second Þ F = ´ ´ ´ ´ = - - - 1 10 10 663 10 10 19 34 9 8 6.63 N 10. Here out put en ergy = 60 W/s Pressure p = ´ ´ = ´ - 2 60 3 10 8 4 10 N 7 de-Broglie wavelength 11. Here m = Þ = ´ - 5 5 10 3 g m kg, v = 340 m/s by de-Broglie hypothesis wavelength l = = ´ ´ ´ - - h mv 6.62 10 5 10 340 34 3 Þ l = ´ - 3.9 10 m 34 Since l is too small. No wave like property is exhibit. 12.(a) l e e h m v = = ´ ´ ´ ´ - - 6.6 9.1 4.7 10 10 10 34 31 6 = ´ - 1.55 m 10 10 (b) l p = ´ ´ ´ ´ ´ - - - 6.6 9.1 4.7 10 1836 10 10 34 31 6 = ´ - 8.44 m 10 14 13. (a) l = h p Þ p h = = ´ ´ - - l 6.6 2.8 10 10 34 10 Þ p = ´ - 2.37 kg - m /s 10 24 (b) Q p m K e 2 2 = Þ K p m e = 2 2 Þ K = ´ ´ ´ - - ( ) 2.37 9.1 10 2 10 24 2 31 Þ K = ´ - 3.07 J 10 18 K K ( ) in eV in J 1.6 3.07 1.6 = ´ = ´ ´ - - - 10 10 10 19 18 19 Þ K =19.2 eV 14. Here T = ° + ° = 273 20 293 K v RT M rms = 3 Þ l = h Mv rms Þ l = h MRT 3 = ´ ´ ´ ´ ´ ´ - - 6.6 9.1 8.31 10 3 1836 10 293 34 31 Þ l =1.04 Å 15. For hy dro gen like atom E K = - Here E = - 3.4 eV Þ K = = ´ ´ - 3.4 eV 3.4 1.6 J 10 19 l = = h p h m K e 2 = ´ ´ ´ ´ ´ ´ - - - 6.6 9.1 3.4 1.6 10 2 10 10 34 31 19 Þ l = 6.663 Å 16. In Bohr model the ve loc ity of elec tron in nth or bit is given by U e nh n = 2 0 2e Putting the values of e h , , e 0 and n = 1, we get U 1 7 10 = ´ 2.19 m/s and U 4 6 10 = ´ 2.19 4 m/s 63 60 p cos 60 p cos 60° p sin 60° p sin 60 pRead More
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