The primary of a step-down transformer has 240 turns and is connected to a 120 V rms line. The secondary is to supply 26 A at 6 V.

(a) Find the current in the primary.
_________A

(b) Find the number of turns in the secondary, assuming 100% efficiency.
_________

A 8 µF capacitor is charged to 33 V and is then connected across a 11-mH inductor.

(a) How much energy is stored in the system?
_________J

(b) What is the frequency of oscillation of the circuit?
________Hz

(c) What is the maximum current in the circuit?
_________A

Respuesta :

Explanation:

Solution (1)

It is given that,

Number of turns in primary coil in step down transformer, [tex]N_P=240[/tex]

Voltage in primary transformer, [tex]V_p=120\ V[/tex]

Current in secondary coil, [tex]I_s=26\ A[/tex]

Voltage in secondary coil, [tex]V_s=6\ A[/tex]

(a) Let [tex]I_P[/tex] is the current in primary coil. It can be calculated using the formula as :

[tex]\dfrac{V_P}{V_s}=\dfrac{I_s}{I_P}[/tex]

[tex]\dfrac{120}{6}=\dfrac{26}{I_P}[/tex]

[tex]I_p=1.3\ A[/tex]

(b) Let [tex]N_s[/tex] is the number of turns in secondary coil. It can be calculated using the formula as :

[tex]\dfrac{V_P}{V_s}=\dfrac{N_P}{N_s}[/tex]

[tex]\dfrac{120}{6}=\dfrac{240}{N_s}[/tex]

[tex]N_s=12\ turns[/tex]

Solution (2)

Capacitance of the capacitor, [tex]C=8\ \mu F=8\times 10^{-6}\ F[/tex]

Voltage, V = 33 V

Inductance, [tex]L=11\ mH=11\times 10^{-3}\ H[/tex]

(a) Let E is the energy stored in the system. It is given by :

[tex]E=\dfrac{1}{2}CV^2[/tex]

[tex]E=\dfrac{1}{2}\times 8\times 10^{-6}\times (33)^2[/tex]

E = 0.00435 J

or

[tex]E=4.35\times 10^{-3}\ J[/tex]

(b) Let f is the frequency of oscillation. It is given by :

[tex]f=\dfrac{1}{2\pi \sqrt{LC} }[/tex]

[tex]f=\dfrac{1}{2\pi \sqrt{11\times 10^{-3}\times 8\times 10^{-6}} }[/tex]

f = 536.51 Hz

(c) The maximum current in the circuit is,

[tex]I=\sqrt{\dfrac{2E}{L}}[/tex]

[tex]I=\sqrt{\dfrac{2\times 0.00435}{11\times 10^{-3}}}[/tex]

I = 0.88 A

Hence, this is the required solution.

Answer:

Explanation:

Np = 240

Vp = 120 V

Is = 26 A

Vs = 6 V

(a) According to the principle of transformer

Ip/ Is = Vs / Vp

Ip / 26 = 6 / 120

Ip = 1.3 A

(b) Ns / Np = Vs / Vp

Ns / 240 = 6 / 120

Ns = 12

....................................

C = 8 x 10^-6 F

V = 33 V

L = 11 m H = 0.011 H

(a) Energy stored, U = 0.5 x CV² = 0.5 x 8 x 10^-6 x 33 x 33

U = 4.356 x 10^-3 J

(b) Let f be the frequency of oscillations

[tex]f=\frac{1}{2\pi \sqrt{LC}}[/tex]

[tex]f=\frac{1}{2\times 3.14 \sqrt{0.011\times 8\times10^{-6}}}[/tex]

f = 536.78 Hz