What i couldn't understand from this is whe he was getting the value for cosa he got 5/13 at which 13 is the hypotenuse but how did he get the value 5? If possible can you elaborate or explain that?

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Chapter1: Units, Trigonometry. And Vectors
Section: Chapter Questions
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What i couldn't understand from this is whe he was getting the value for cosa he got 5/13 at which 13 is the hypotenuse but how did he get the value 5? If possible can you elaborate or explain that?
21.5 Electric-Field Calculations
705
21.22 Electric field at three points, a, b, and e, set up by
charges q, and 92, which form an electric dipole.
(c) Figure 21.22 shows the directions of E, and E2 at c. Both
vectors have the same x-component:
Eia = Em = E,, cos œ = (6.39 × 10' N/C)(÷)
= 2.46 × 10° N/C
From symmetry, E, and E,, are equal and opposite, so their sum
is zero. Hence
E = 2(2.46 × 10 N/C)i = (4.9 × 10' N/C)i
EVALUATE: We can also find E using Eq (21 7) for the field of a
point charge. The displacement vector Fị from q to point e is
r Cosai + sinaj. Hence the unit veetor that points from
130 cm
13.0 cm
41 to point c
unit vector that points from q. to point e has the opposite x-
component but
We can now use Eq. (21.7) to write the fields E and E, at e in
vector form
rto c is the same for both charges.
rr= CONal + sinaj. By symmetry. the
same v-component , = -cosaf + sinaj.
their sum. Since q1
4i and the distance
6.0
E = È +E˸=
42
4.0
ta) Ata. E, and E, até both directed to the righL SO
(2 cusai)
12 10
(0.13 m
Ē, = L i + Ei = (9.8 × 10 NC
= 2(9.0 X 10 N mC
(b) At , E, is directed to the left and E, is directed to the
tight, so
= (49 x 10 N/C)
Transcribed Image Text:21.5 Electric-Field Calculations 705 21.22 Electric field at three points, a, b, and e, set up by charges q, and 92, which form an electric dipole. (c) Figure 21.22 shows the directions of E, and E2 at c. Both vectors have the same x-component: Eia = Em = E,, cos œ = (6.39 × 10' N/C)(÷) = 2.46 × 10° N/C From symmetry, E, and E,, are equal and opposite, so their sum is zero. Hence E = 2(2.46 × 10 N/C)i = (4.9 × 10' N/C)i EVALUATE: We can also find E using Eq (21 7) for the field of a point charge. The displacement vector Fị from q to point e is r Cosai + sinaj. Hence the unit veetor that points from 130 cm 13.0 cm 41 to point c unit vector that points from q. to point e has the opposite x- component but We can now use Eq. (21.7) to write the fields E and E, at e in vector form rto c is the same for both charges. rr= CONal + sinaj. By symmetry. the same v-component , = -cosaf + sinaj. their sum. Since q1 4i and the distance 6.0 E = È +E˸= 42 4.0 ta) Ata. E, and E, até both directed to the righL SO (2 cusai) 12 10 (0.13 m Ē, = L i + Ei = (9.8 × 10 NC = 2(9.0 X 10 N mC (b) At , E, is directed to the left and E, is directed to the tight, so = (49 x 10 N/C)
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