GCSE PHYSICS - MAGNETISM AND ELECTROMAG - LESSON 19 - transformer part 1

How Do Transformers Work?

Introduction to Transformers

• A transformer is a device that transfers electric current and voltage from a primary circuit to a secondary circuit using a magnetic field through a magnetic core.

• The core is made from magnetically soft material, such as iron, which can be rapidly magnetized and demagnetized.

Working Principle of Transformers

• A changing input voltage in the primary coil leads to a changing current, producing a changing magnetic field in the iron core.

• This changing magnetic field induces a change in current in the secondary coil, resulting in a corresponding change in voltage due to Ohm's law.

• It’s crucial for the current to be changing; if the magnetic field is fixed, induction will not occur.

Frequency and Efficiency

• In many countries, including the UK, electricity is transmitted at 50 Hertz alternating current (AC), meaning the magnetic field changes 50 times per second.

• Using magnetically soft materials prevents energy loss as heat; otherwise, some electrical energy would convert into heat within the core.

Transformer Equations

• The relationship between input voltage (VP), output voltage (VS), and number of turns in coils (NP for primary and NS for secondary) can be expressed mathematically:

• [ V_P/V_S = N_P/N_S ]

• This equation can also be rearranged to find unknown variables based on given values typically encountered in exams.

Power Considerations

• Soft iron cores used are nearly 100% efficient with minimal energy lost as heat. Thus:

• Input power P_in = V_P times I_P

• Output power P_out = V_S times I_S

• Assuming efficiency: V_P I_P = V_S I_S

Types of Transformers

• There are two main types of transformers:

• Step-Up Transformer: Output voltage is greater than input voltage.

• Step-Down Transformer: Output voltage is less than input voltage.

Understanding Transformers: Step-Up and Step-Down

The Basics of Transformer Operation

• The relationship between the output voltage in a transformer and the input voltage is defined by the equation: V_secondary = V_primary times fracN_secondaryN_primary , where N represents the number of turns in each coil.

• A step-up transformer increases output voltage when the number of turns in the secondary coil is greater than that in the primary coil, resulting in higher voltage output.

• Conversely, a step-down transformer decreases output voltage when there are fewer turns in the secondary coil compared to the primary, leading to lower voltage output.