Unit 5: Electrical and electronic design
LO2: Understand the application of electromagnetism
in electrical design – Transformers
Learner activity sheet
Transformers have changed little over the last 100 years.
They work on the principle of mutual induction – to change the values of alternating voltages and
currents.
They range in size – from miniature ones used in electronics to large ones used in power distribution.
Activity 1
1. Investigate how a transformer works – and explain how it transforms or changes voltage and
current.
2. Assuming a no loss transformer – state the formulae, giving the relationship between primary and
secondary turns, and primary and secondary current and voltage
3. Explain what is meant by both a ‘step up’ and a ‘step down’ transformer.
March 2015
Activity 2
1. An ideal transformer used in a battery charging circuit is connected to a 240 V mains supply, and
supplies a 12 V load of 150 W. Calculate the transformer turns ratio, and the current that is taken
from the supply.
2. A power distribution transformer has 500 primary turns and 2000 secondary turns. If the primary
voltage is 240 V, determine the secondary voltage and whether this is a step-up or step-down
transformer. The transformer is ideal.
March 2015