3.4 Transformer

A transformer is 80% efficient with the primary voltage of 240 V and the secondary voltage of 12 V. If the current in the secondary circuit is 4 A, calculate the current in the primary circuit.

• 6.50 A

• 5.50 A

• 1.00 A

• 0.25 A

The number of turns between each pair of output terminals of a transformer is shown in the diagram 25. Which of the following 2 terminals produced the output voltage 12V.

• P and Q

• Q and R

• R and S

• P and R

The purpose of using laminated iron core in a transformer is to

• reduce resistance

• reduce eddy current

• prevent flux leakage

• magnetized and demagnetized iron core easily

Diagram shows a transformer. Which of the following method is used to increase the efficiency of the transformer?

• use a thinner wire

• use solid iron core

• use steel iron core

• use laminated iron core

Diagram shows an ideal transformer. What is the value of the output voltage?

• 7.2 V

• 20 V

• 200 V

• 3125 V

An ideal transformer has 400 turns on the primary coil and 580 turns on the secondary coil.

When a 240 V supply is acted on the primary coil, an 8 A current flows through it. What is the value of the output current at the secondary coil?

• 1.8 A

• 2.6 A

• 4.3 A

• 5.5 A

Diagram shows a transformer that has efficiency of 80 %. If it produces an output power of 100 W, what is the amount of current flowing in the primary coil?

• 6.25 A

• 5.15 A

• 4.00 A

• 3.75 A

Diagram shows a simple transformer with bulb lights up at normal brightness. What will happen if the alternating current, a.c input is replaced by a 3 V battery?

• The bulb blows

• The brightness of the bulb decreases

• The brightness of the bulb increases

• The bulb does not light up

The input current and the output current of a transformer are 0.5 A and 4.0 A respectively. If the transformer loss it power of 25% and the number of turns of the secondary coil is 150 turns, find the number of turns of the primary coil.

• 14

• 25

• 1600

• 4800

Diagram shows a transformer with a bulb, 12 V, 6 W lights with normal brightness. What happens to the bulb when the number of turns in secondary coil decreases to 20 turns?

• Blown up

• Dimmer

• Brighter

• The brightness unchanged