Lesson_3.1_Homework_and_Solutions

# Lesson_3.1_Homework_and_Solutions - × 10 4 × 2 × 10-3 =...

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Lesson 3.1 Homework Solutions 1. Q = CV = 15 × 10 -12 × 1.5 = 2.25 × 10 -12 C 2. 2 1 2 2 1 1 2 1000 /1000 (2 ) 2000 2 2 /100 2 0 o o o o o o A R C R d R A R C R C d R C C ε ε π = = = = = = = = 3. The electric field between two parallel plates is given by 5 12 6 2 6 4 9 2.8 10 8.85 10 2.478 10 5. 2.478 10 2 10 2 1 1 0 o o E E C m Q A C σ - - - - - - = = = × × × = × = × = = × × × 4. C = 0.8 × 10 -6 F, Q = 72 × 10 -6 C, d = 2 × 10 -3 m. 6 1 6 3 4 4.5 72 1 10 0 90 0.8 10 90 2 10 Q V V C V m V m V E d - - - - × = = = × = = = × × 5. For an air parallel plate capacitor: o A C d = (i) Inserting the metal plates in between the plates of the capacitor effectively reduces the gap from d to d – l . Therefore, the new capacitance C’ is ' o A C d l = - (ii) If l, = (2/3)d, the new capacitance C’ is ' 3 3 2 1 3 3 o o o A A A C C d d d d = = = = -

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6. We have 4 9 2 12 2 9 2 9 8 4 9 2 2 1 0.01 1.13 10 8.85 10 ( ) 1.13 10 ( ) 1.13 10 1.13 10 3.60 1 3.36 10 33.6 1.9 10 19 0 o o A C d Cd A m i A l ii A l m km r m k r m m r ε π - = × = = = × × = = × = = = × = = × = × × = = × 7. 6 6 6 0 0 0 5 10 12 0 10 10 12 5 10 1 1 ( ) 20 10 1 ( ) 20 10 0.625 1.875 Q Q Q J q E Vdq dq qdq C C i E qdq ii E qd J q - - - × - × - × = = = = = × = = × 8. (i) If E is the electric field and d the plate separation, the voltage across the plates is: V = Ed = 2
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Unformatted text preview: × 10 4 × 2 × 10-3 = 40 V . (ii) 6 7 2 7 3 2 2 12 10 10 2.5 10 40 2.5 10 2 10 17.98 8.8 24 5 10 4. o o o Q C C V A C d Cd A r C r r m d m ε π πε-----× = = = × = = = × × × = = = × × = 9. (i) Energy required to charge the capacitor to 100 V is: E = (1/2)CV 2 = (1/2) × 3 × 10-6 × 100 2 = 0.015 J = 15 mJ (ii) energy required to charge it to 200 V is : E = (1/2)CV 2 = (1/2) × 3 × 10-6 × 200 2 = 0.065 J = 65 mJ Therefore the additional energy required to charge it from V = 100 v to V = 200 V is 65 mJ – 15 mJ = 45 mJ . 10. κ mica = 5.4 , A = π r 2 = π (0.05) 2 = 7.9 × 10-3 m 2 . 2 10 1 3 3 5.4 8.85 10 7.9 10 3.2 10 1.2 10 o A C d F κε----× × × × = = = × ×...
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## This note was uploaded on 05/01/2011 for the course PHY 2049 taught by Professor George during the Spring '11 term at Edison State College.

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Lesson_3.1_Homework_and_Solutions - × 10 4 × 2 × 10-3 =...

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