An ideal transformer produces an output of 6 volts when an input of 240 volts is applied.

What change would be needed to produce an output of 12 volts, using the same input voltage?

1. Increase the number of turns on the primary coil
2. Decrease the number of turns on the primary coil
3. Increase the resistance connected to the secondary coil
4. Decrease the resistance connected to the secondary coil

A 40 V AC generator and an ideal transformer are used to supply power. The diagram below shows the generator and the transformer supplying 240 V to a resistor with a resistance of 1200 \( \Omega \).
 

Question 5

Which of the following correctly identifies the parts labelled \(\text{X}\) and \(\text{Y}\), and the function of the transformer?

\begin{align*}
\begin{array}{l}
\rule{0pt}{2.5ex} \ \rule[-1ex]{0pt}{0pt}& \\
\rule{0pt}{2.5ex}\textbf{A.}\rule[-1ex]{0pt}{0pt}\\
\rule{0pt}{2.5ex}\textbf{B.}\rule[-1ex]{0pt}{0pt}\\
\rule{0pt}{2.5ex}\textbf{C.}\rule[-1ex]{0pt}{0pt}\\
\rule{0pt}{2.5ex}\textbf{D.}\rule[-1ex]{0pt}{0pt}\\
\end{array}
\begin{array}{|l|l|l|}
\hline
\rule{0pt}{2.5ex}\quad \ \ \ \text{Part X}\quad \rule[-1ex]{0pt}{0pt}&\ \ \  \quad \text{Part Y} \quad& \text{Function of transformer} \\
\hline
\rule{0pt}{2.5ex}\text{primary coil}\rule[-1ex]{0pt}{0pt}&\text{secondary coil} & \text{step-down}\\
\hline
\rule{0pt}{2.5ex}\text{primary coil}\rule[-1ex]{0pt}{0pt}& \text{secondary coil}&\text{step-up}\\
\hline
\rule{0pt}{2.5ex}\text{secondary coil}\rule[-1ex]{0pt}{0pt}& \text{primary coil} &\text{step-down}\\
\hline
\rule{0pt}{2.5ex}\text{secondary coil}\rule[-1ex]{0pt}{0pt}& \text{primary coil} &\text{step-up}\\
\hline
\end{array}
\end{align*}

Question 6

Which one of the following is closest to the current in the primary circuit?

1. \(0.04\ \text{A}\)
2. \(0.20\ \text{A}\)
3. \(1.20\ \text{A}\)
4. \(1.50\ \text{A}\)

An ideal transformer has an input DC voltage of 240 V, 2000 turns in the primary coil and 80 turns in the secondary coil.

The output voltage is closest to

1. 0 V
2. 9.6 V
3. 6.0 × 10\(^{3}\) V
4. 3.8 × 10\(^{7}\) V

A mobile phone charger uses a step-down transformer to transform 240 V AC mains voltage to 5.0 V. The mobile phone draws a current of 3.0 A while charging. Assume that the transformer is ideal and that all readings are RMS.

Calculate the current drawn from the mains during charging?   (2 marks)

A transformer is used to provide a low-voltage supply for six outdoor garden globes. The circuit is shown in Figure 3. Assume there is no power loss in the connecting wires. 
 

The input of the transformer is connected to a power supply that provides an AC voltage of 240 V. The globes in the circuit are designed to operate with an AC voltage of 12 V. Each globe is designed to operate with a power of 20 W.

1. Assuming that the transformer is ideal, calculate the ratio of primary turns to secondary turns of the transformer.  (1 mark)

2. Calculate the current in the primary coil of the transformer.  (2 marks)

3. Explain why the input current to the primary coil of the transformer must be AC rather than constant DC for the globes to shine.  (2 marks)

An ideal transformer is connected to a 240 V AC supply. It has 300 turns on the primary coil and 50 turns on the secondary coil.

It is connected in the circuit with two identical light globes, \(X\) and \(Y\), as shown.
 

1. Calculate the voltage across light globe \(X\) when the switch is open. (2 marks)
   

   --- 4 WORK AREA LINES (style=lined) ---

2. Explain why, after the switch has been closed, the current in the primary coil is different from when the switch is open.  (3 marks)
   

   --- 7 WORK AREA LINES (style=lined) ---

The diagram shows a circuit containing two ideal transformers connected with an ammeter. The current through the load is 5.0 A.
 

What is the reading on the ammeter?   (3 marks)

The diagram shows a label on a transformer used in an appliance.

     
Explain why the information provided on the label is not correct. Support your answer with calculations.   (3 marks)

The diagram shows an ideal transformer.
 

When the switch is closed, the pointer on the galvanometer deflects.

How could the size of the deflection be increased?

1. Decrease the number of primary coils
2. Decrease the number of secondary coils
3. Replace the iron core with a copper core
4. Place a resistor in series with the galvanometer

An ideal transformer has 20 turns on the primary coil and an input voltage of 100 V.

How many turns are there on the secondary coil if the output voltage is 400 V ?

1. 4
2. 5
3. 80
4. 400

In a certain ideal transformer, the current in the secondary coil is four times as large as the current in the primary coil.

Which row of the table correctly identifies the type of transformer and the ratio of turns?

\begin{align*}
\begin{array}{l}
\rule{0pt}{0.5ex}\textit{} & \textit{} \\
\textit{}\rule[-0.5ex]{0pt}{0pt}& \textit{} \\
\rule{0pt}{2.5ex}\textbf{A.}\rule[-1ex]{0pt}{0pt}\\
\rule{0pt}{2.5ex}\textbf{B.}\rule[-1ex]{0pt}{0pt}\\
\rule{0pt}{2.5ex}\textbf{C.}\rule[-1ex]{0pt}{0pt}\\
\rule{0pt}{2.5ex}\textbf{D.}\rule[-1ex]{0pt}{0pt}\\
\end{array}
\begin{array}{|l|c|}
\hline
\rule{0pt}{0.5ex} \quad \textit{Type of} & \textit{Ratio of turns in primary coil} \\
\textit{transformer}\rule[-0.5ex]{0pt}{0pt}& \textit{to turns in secondary coil} \\
\hline
\rule{0pt}{2.5ex}\text{Step up}\rule[-1ex]{0pt}{0pt}&4:1\\
\hline
\rule{0pt}{2.5ex}\text{Step up}\rule[-1ex]{0pt}{0pt}& 1:4\\
\hline
\rule{0pt}{2.5ex}\text{Step down}\rule[-1ex]{0pt}{0pt}& 4:1 \\
\hline
\rule{0pt}{2.5ex}\text{Step down}\rule[-1ex]{0pt}{0pt}& 1:4 \\
\hline
\end{array}
\end{align*}