Chapter 21, Problem 74GP

To determine

(a)

Whether the transformer step up or step down

Answer to Problem 74GP

Solution:

The transformer step up or step down the answer will be step down

Explanation of Solution

Given info:

$\begin{array}{l}P=45\text{W}\\ V=12\text{V}\\ V_0=120\text{V}\end{array}$

Formula used:

$P=I_s{V}_s$

Where,

$\begin{array}{l}P=45\text{W}\\ V=12\text{V}\\ V_0=120\text{V}\end{array}$

Calculation:

The transformer step down because $V_s<V_P$

To determine

(b)

The current in the secondary coil

Answer to Problem 74GP

Solution:

The current in the secondary coil will be $3.8\text{A}$

Explanation of Solution

Given info:

$\begin{array}{l}P=45\text{W}\\ V=12\text{V}\\ V_0=120\text{V}\end{array}$

Formula used:

$P=I_s{V}_s$

Where,:

$\begin{array}{l}P=45\text{W}\\ V=12\text{V}\\ V_0=120\text{V}\end{array}$

Calculation:

$P_s=I_s{V}_s\to I_s=\frac{P_s}{V_s}=\frac{45\text{W}}{12\text{V}}=3.8\text{A}$

To determine

(c)

The current in the coil

Answer to Problem 74GP

Solution:

The current in the coil will be $0.38\text{A}$

Explanation of Solution

Given info:

$\begin{array}{l}P=45\text{W}\\ V=12\text{V}\\ V_0=120\text{V}\end{array}$

Formula used:

P=IV

Where,

$\begin{array}{l}P=45\text{W}\\ V=12\text{V}\\ V_0=120\text{V}\end{array}$

Calculation:

$P_p=I_p{V}_p\to I_p=\frac{P_p}{V_p}=\frac{45\text{W}}{120\text{V}}=0.38\text{A}$

To determine

(d)

The resistance of the bulb when on

Answer to Problem 74GP

Solution:

The resistance of the bulb when on will be $3.2\text{A}$

Explanation of Solution

Given info:

$\begin{array}{l}P=45\text{W}\\ V=12\text{V}\\ V_0=120\text{V}\end{array}$

Formula used:

V=IR

Where,

$\begin{array}{l}P=45\text{W}\\ V=12\text{V}\\ V_0=120\text{V}\end{array}$

Calculation:

$V_s=I_{s}R\to R=\frac{V_s}{I_s}=\frac{12\text{V}}{3.75\text{A}}=3.2\text{Ω}$