Transformers

A secondary coil of a transformer has 500 windings. It was supplied with 200 V. How many windings needed at primary coil to produce 100 V.

Tags

NGSS.HS-PS3-1

Select the correct characteristics for ideal transformers.

• Zero leakage flux.

• The wire have no resistance.

• No hysteresis or eddy currents.

• Has similar windings at both primary and secondary coils.

Efficiency of a transformer is

• (output current)/(input current) x100%

• (output voltage)/(input voltage) x100%

• (output loss)/(input loss) x100%

• (output power)/(input power) x100%

Tags

NGSS.HS-PS3-1

Laminated insulation are normally used in the transformer:

• To reduce the hysteresis effect

• To increase the hysteresis effect

• To reduce the effect of eddy current

• To increase the effect of eddy current

The primary and secondary induced emfs in two winding transformer are always:

• Antiphase with each other

• In phase with each other

• Equal in magnitude

• Determined by load on transformer secondary

A transformer does not change the following:

• Frequency

• Voltage

• Current

• None of these

Assume primary has 240 turns and secondary has 60 turns. Primary is connected with 120V AC power supply. What is the voltage on the secondary?

• 30 V

• 0.333 V

• 2 V

• 120V

Transformer core are laminated in order to

• reduce hysteresis loss

• reduce hysteresis & eddy current loss

• minimize eddy current loss

• Copper loss

A step-down transformer that has an efficiency of 92.5 percent is used to obtain 28.0 V from a 125 V household potential difference. The current in the secondary circuit is 25.0 A.

a. What is the current in the primary circuit?

b. At what rate is thermal energy generated?

• a. 7 A and b. 50 W

• a. 5.05 A and b. 27 W

• a. 6.05 A and b. 57 W

• a. 9 A and b. 82 W

The electricity received at an electrical substation has a potential difference of 240,000 V. What should the turns ratio of the step-down transformer be to have an output of 440 V?

• 224:3

• 460:7

• 900:1

• 545:1