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IB MYP 4-5 Physics- Transformers – Study Notes

IB MYP 4-5 Physics- Transformers - Study Notes - New Syllabus

IB MYP 4-5 Physics-Transformers – Study Notes

Key Concepts

  • Transformers 

IB MYP 4-5 Physics Study Notes – All topics

IB MYP 4-5 Physics Practice Question - All Topics

Transformers

Transformers

A transformer is a device that changes the voltage of an alternating current (AC) supply.

  • It works on the principle of electromagnetic induction.
  • Transformers only work with AC, not DC, because a changing magnetic flux is required for induction.

Construction

  • Primary coil: Connected to the AC input supply.
  • Secondary coil: Connected to the output circuit (where voltage is required).
  • Iron core: Soft iron core links both coils and increases magnetic flux.

Principle of Operation

  • An AC current in the primary coil produces a changing magnetic flux in the iron core.
  • This changing flux induces an emf in the secondary coil according to Faraday’s law.
  • The voltage induced depends on the ratio of turns in the coils.

Transformer Equation

\(\dfrac{V_s}{V_p} = \dfrac{N_s}{N_p}\)

  • \(V_s\) = voltage across secondary coil
  • \(V_p\) = voltage across primary coil
  • \(N_s\) = number of turns in secondary coil
  • \(N_p\) = number of turns in primary coil

Power conservation (ideal case):

\(V_p I_p = V_s I_s\)

Types of Transformers

  • Step-up transformer: Increases voltage (\(N_s > N_p\)).
  • Step-down transformer: Decreases voltage (\(N_s < N_p\)).

Efficiency of a Transformer

  • Defined as \(\eta = \dfrac{P_{out}}{P_{in}} \times 100 \%\).
  • Practical efficiency is usually high (90–99%).
  • Energy losses occur due to:
    • Copper losses (resistance of coils)
    • Eddy currents in the core
    • Magnetic hysteresis in the iron core
    • Leakage of magnetic flux

Applications

  • Power transmission (step-up at power stations, step-down at substations)
  • Battery chargers
  • Doorbell circuits
  • Electronic devices (phone/laptop adapters)

Example:

A transformer has 200 turns in the primary coil and 1000 turns in the secondary coil. If the input voltage is 230 V, find the output voltage.

▶️ Answer/Explanation

Step 1: Formula: \(\dfrac{V_s}{V_p} = \dfrac{N_s}{N_p}\).

Step 2: \(\dfrac{V_s}{230} = \dfrac{1000}{200} = 5\).

Step 3: \(V_s = 230 \times 5 = 1150 \, V\).

Final Answer: \(\boxed{1150 \, V}\) (Step-up transformer).

Example:

A transformer has 1000 turns in the primary coil and 100 turns in the secondary coil. It supplies 5 A at 12 V in the secondary coil. Assuming 100% efficiency, find the primary current if the input voltage is 120 V.

▶️ Answer/Explanation

Step 1: Power in = Power out.

Step 2: \(V_p I_p = V_s I_s\).

Step 3: \(120 \times I_p = 12 \times 5 = 60\).

Step 4: \(I_p = \dfrac{60}{120} = 0.5 \, A\).

Final Answer: \(\boxed{0.5 \, A}\).

Example:

Explain why step-up transformers are used at power stations before transmitting electricity over long distances.

▶️ Answer/Explanation

Step 1: Energy loss in transmission wires is \(P_{loss} = I^2 R\).

Step 2: For a fixed power, increasing voltage reduces current \((P = VI)\).

Step 3: Lower current → smaller \(I^2 R\) losses in wires.

Final Answer: Step-up transformers reduce transmission losses by increasing voltage and reducing current.

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