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A -5.45 nC point charge is on the x axis at x = 1.35 m . A second point charge Q is on the x axis at -0.595 m. What must be the sign and magnitude of Q for the resultant electric field at the origin to be 45.0 N/C in the +x direction? What must be the sign and magnitude of Q for the resultant electric field at the origin to be 45.0 N/C in the −x direction?

Respuesta :

Answer:

a)Q= + 0.71 nC , For the resultant electric field at the origin to be 45.0 N/C in the +x direction

b)Q= -2.83nC ,for the resultant electric field at the origin to be 45.0 N/C in the −x direction

Explanation:

Conceptual analysis

The electric field at a point P due to a point charge is calculated as follows:

E = k*q/d²

E: Electric field in N/C

q: charge in Newtons (N)

k: electric constant in N*m²/C²

d: distance from charge q to point P in meters (m)

The electric field at a point P due to several point charges is the vector sum of the electric field due to individual charges.

Equivalences

1nC= 10⁻9 C

Data

k = 8.99*10⁹ N×m²/C²

q₁ =+5.45nC = 3*10⁻⁹C

d₁ =1.35 m

d₂ = 0.595m

a)Problem development : sign and magnitude of Q for the resultant electric field at the origin to be 45.0 N/C in the +x direction

We make the algebraic sum of fields at at the origin :

[tex]E_{o} =E_{q} +E_{Q}[/tex] Equation (1)

[tex]E_{q} =\frac{k*q_{1} }{d_{1}{2}  }[/tex]

Calculation of E(q)

[tex]E_{q} =\frac{8.99*10^{9} *5.45*10^{-9} }{1,35^{2} }[/tex]

[tex]E_{q} =26.88\frac{N}{C}[/tex] : in the +x direction .As the charge is negative, the field enters the charge

We replace [tex]E_{o}[/tex] and [tex]E_{q}[/tex] in the equation (1)

[tex]45=26.88+E_{Q}[/tex]

[tex]E_{Q} =45-26.88[/tex]

[tex]E_{Q} = 18.12 N/C[/tex] : in the +x direction .

Sign and magnitude of Q

Q must be positive for the field to abandon the load in the +x

[tex]E_{Q} =\frac{k*Q}{d_{2}^{2} }[/tex]

[tex]18.12=\frac{8.99*10^{9}*Q }{0.595^{2} }[/tex]

[tex]Q=\frac{18.12*0.595^{2} }{8.99*10^{9} }[/tex]

Q=0.71*10⁻⁹ C =0.71 nC

b)Sign and magnitude of Q for the resultant electric field at the origin to be 45.0 N/C in the −x direction

We make the algebraic sum of fields at at the origin :

[tex]E_{o} =E_{q} +E_{Q}[/tex]

[tex]-45=26.88+E_{Q}[/tex]

[tex]-71.88=E_{Q}[/tex]

[tex]71.88=\frac{8.99*10^{9} *Q}{0.595^{2} }[/tex]

Q= 2.83*10⁻⁹ C

Q= -2.83nC

Q must be negative for the field to enters the charge in the −x direction

The magnitude and sign of Q is given by the required magnitude and

sign of the charge at the origin due to the sum of the charges.

Responses:

  • The sign and magnitude of Q when the charge is 45 N/C in the +x direction is, Q ≈ 2.83 nC

  • The sign and magnitude of Q when the charge is 45 N/C n the -x direction is, Q ≈ -713.4 pC

How can the charge of the two particles at the origin be found?

The charge at the origin is given as follows;

When the charge at the origin is 45.0 N/C, we have;

[tex]45 = \mathbf{\dfrac{8.99 \times 10^{9} \times -5.45 \times ^{-9} }{1.35^2} + \dfrac{8.99 \times 10^{9} \times Q} {(-0.595)^2}}[/tex]

Which gives;

[tex]Q = \dfrac{\left(45 - \dfrac{8.99 \times 10^{9} \times -5.45 \times ^{-9} }{1.35^2} \right) \times (-0.595)^2}{8.99 \times 10^{9} } \approx \mathbf{2.83 \times 10^{-9}}[/tex]

When the charge at the origin is [tex]E_0[/tex] = 45 N/C, we have;

  • Q ≈ 2.83 × 10⁻⁹ C = 2.83 nC

When the charge at the origin is [tex]E_0[/tex] = 45 N/C in the -x direction, we have;

[tex]Q = \dfrac{\left(-45 - \dfrac{8.99 \times 10^{9} \times -5.45 \times ^{-9} }{1.35^2} \right) \times (-0.595)^2}{8.99 \times 10^{9} } \approx -7.134 \times 10^{-10}[/tex]

Therefore;

The charge at the origin is [tex]E_0[/tex] = 45 N/C in the -x direction, we have;

  • Q ≈ -7.134 × 10⁻¹⁰ C = -713.4 pC

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