Class 10 > Unit # 16: Electromagnetism > Transformers

Talha's Physics Academy

Construction, Working, Types, and Applications of a Transformer

Transformer: Construction and Working

"A transformer is an electrical device that makes use of mutual induction to step up or step down an alternating electromotive force (EMF) without changing its frequency."

Construction

A transformer consists of two coils that are magnetically linked through a laminated iron core but are electrically isolated from one another:

• Primary Coil ($N_p$ turns): The input coil connected to the alternating current (A.C.) power source.
• Secondary Coil ($N_s$ turns): The output coil that delivers the transformed power to the load circuit.
• Iron Core: Provides a low-reluctance path for the magnetic flux to ensure efficient linkage between the primary and secondary coils.

Working Principle

When an alternating current flows through the primary coil, it produces a varying magnetic field in the iron core. This changing magnetic flux is transmitted through the core to the secondary coil, where it induces an alternating EMF via mutual induction. The secondary voltage ($V_s$) is proportional to the primary voltage ($V_p$) and depends on the turns ratio:

$$\frac{V_s}{V_p} = \frac{N_s}{N_p}$$

Fig: Basic structure of a transformer showing primary and secondary coils wrapped around a laminated iron core.

Types of Transformers

• Step-Up Transformer: Increases the alternating voltage ($V_s > V_p$), meaning the number of secondary turns exceeds the primary turns ($N_s > N_p$). Example: Voltage stabilizers.
• Step-Down Transformer: Decreases the alternating voltage ($V_s < V_p$), meaning the number of secondary turns is less than the primary turns ($N_s < N_p$). Example: Mobile phone chargers.

Power Relations and Efficiency

For an ideal transformer with 100% efficiency, the input power equals the output power:

$$\text{Power Input} = \text{Power Output}$$

$$V_p I_p = V_s I_s$$

Consequently, current is inversely proportional to voltage:

$$\frac{I_s}{I_p} = \frac{V_p}{V_s} = \frac{N_p}{N_s}$$

Daily Life Uses and Applications of Transformers

1. Power Transmission: Electric power generated at power plants is stepped up to very high voltages for long-distance transmission over power lines. This drastically reduces current ($I$), minimizing resistive power losses ($P = I^2 R$) along the wires before stepping it back down for consumer use.
2. Voltage Stabilizers: Stabilizers utilize internal transformers to automatically step up or step down fluctuating grid voltages to safeguard sensitive household electrical appliances.
3. Battery Chargers: Mobile chargers, laptop adapters, and battery chargers use step-down transformers to convert high mains A.C. voltage into safe, low-voltage alternating current before rectification.
4. Circuit Breakers: Integrated transformers within protection circuitry help monitor current levels and work in tandem with breaker mechanisms to prevent severe damage from high-voltage surges.
5. Air Conditioners (AC): Air conditioning units rely on transformer-coupled control circuits to handle heavy inductive loads safely and ensure long-term reliable operation.

© 2026 Talha's Physics Academy. All rights reserved.