Transformer example problem

Problem:

An ideal transformer with a 300 turn primary connected to a 480 V, 60 Hz supply line is to output 120 V from the secondary. If a 100 Ω resistor is connected across the secondary, determine: A) how many turns the secondary must have. B) The current through the resistor, C)The current drawn through the primary.

Solution:

Part A:

$\frac{V_1}{V_2}=\frac{N_1}{N_2}$

Where $V_1=$Voltage across primary, $V_2=$Voltage across secondary, $N_1=$ Number of turns in primary, $N_2=$ Number of turns in secondary

$$\begin{gathered} \frac{480 \\ volts}{120 \\ volts}=\frac{300}{N_2} \end{gathered}$$

$$\begin{gathered} N_2=\frac{300\cdot 120}{480}\Rightarrow N_2=75 \\ turns \end{gathered}$$

Part B:

The voltage across the secondary is given as 100 volts. Thus the current by ohms law: $V=i\cdot R$